Thursday, September 23, 2010

2.6b Essential Physical Science

Physician's Notebooks 2  - - See Homepage    
Update  15 Feb. 2019  Reading the following sections may increase scores on tests -- SAT, MCAT, TOEFL, IQ - and get a free or low-cost education scholarship. A lot of secrets to effortlessly help memorization are included in the writing. This is particularly important in the medical sciences. But also the general reader should get benefit from her or his increasing knowledge
Note: this section is packed with useful information. A reader intent on learning it, should read each small segment slowly and separately in the order given and re read to consolidate. And contemplate what you have read in your repose period just after that reading also checking unclear fact in Wikipedia on the Internet
2.6b: Intro to Chemistry & Physics - Structure of Matter:  This section gives the science essential for success in our modern world and to consider yourself "cultured" in the deepest sense in our modern world.  Below are the the sections in order of appearance. To read each separately, use search & find or scroll down 
.Matter - What is it and what is it not? 
The Atomic Theory 
Elements & Compounds 
 X-rays and Radioactivity 
Sub Atomic Structures - Electrons, Protons & Neutrons 
Atoms and Molecules are, respectively, the basis of Elements and Compounds
Atomic Structure of Atoms of the Different Elements 
Electrons are not points, they are Orbitals 
Atomic Mass/Atomic Weight/Isotopes 
What is the difference between “mass” and “weight”? 
Avogadro’s Law and Number  
Notation for chemicals is a shortcut
        (3-Dimensional) Radicals and their Notation
Ions & Ionic Compounds  
Organic and Inorganic; Naming Compounds
Cyclic Molecules and their Radicals 
Electron Sharing in Chemical Bonds 
Chemical Equations 
Aqueous Solution, Concentration, Acid/Base  
The Hydration Process  
The 3 States of Matter as well as Temperature 
About Gases & Atmospheric Pressure  
Energy, Waves, EMG Radiation & Spectrum 

Matter - What is it and what is it not?  Matter is anything that occupies space and has mass. Everything we can touch and see is matter but it also includes things we cannot touch and see like air. Matter is so widespread that the real question is: What is not matter? A vacuum is the absence of matter, but no absolute vacuum exists because, even in the most extreme human-created vacuum, there are thousands of atoms. The concept of vacuum has an important relation to matter because matter is composed of basic particles – atoms, ions, molecules - and separating these particles is the spatial nothingness of vacuum. When we look about, we see pieces of matter - substances of shape, color, consistency, smell: A book, water, a boy, wood. Or if it is an invisible kind of matter, we detect it by its other properties: we smell cooking gas and we become aware of air by seeing that animals rapidly die without it. The kind of matter we can see – water, metal, paper – is substance. Actually, most things we come in contact with are mixtures of two or more substances in which each retains identity and can be separated out (e.g., boiling down a mix of salt in water, and separately collecting each one as the salt residue and the steam).  
        The Atomic Theory  The idea that matter is made of basic particles named atoms goes back to the Ancient Greek philosophers. The original meaning of atom is a unit of matter that cannot be reduced further. Imagine you have a magic scissors that can cut an object in two down to subatomic level. You take a piece of gold (chosen because it is an element, and in pure state all its atoms are alike) and scissor it in half. Then take one of the halves and scissor it in half, and so on, continuing until you scissor down to a piece that is a single atom of gold. Here, with a single atom, you should still be able to determine it is gold from its properties (yellow color, melting point 1,063C, etc.). But with the next scissoring, the resulting halves no longer are gold but a smaller atom of an element whose atoms are exactly half the size of the gold atom. (Such an atom exists and its atoms make up the element technetium) Today we know atoms have been split by huge amounts of energy. But the idea of the indivisible atom was seminal because it went against received opinion of matter as a seamless kind of gas and opened the gates of human imagination to a concept that matter is discontinuous (i.e., not seamless as it appears to us but rather a structure of units separated by empty space). 
 The Ancient Greeks could not test the idea; and it would take till the 1800s to develop The Atomic Theory according to which: 
1) All matter is made up of bonded combinations of the purest substances called elements. 
 2) Each pure element is composed, as its smallest unit, only of its own type of atom recognizable by its shape, mass and by other physical and chemical properties. 
 3) Matter is mostly made up of mixtures of the substances that are chemical combinations of the elements. These are the chemical compounds. 
4) Just as the smallest piece of an element that can be recognized as an element is an atom so the smallest piece of a compound that can be recognized as a chemical compound is a molecule. 
5) All molecules are composed of two or more atoms held together in a chemical bond in fixed proportion of the bonded atoms. Each compound is composed only of its own, unique, identifiable molecules held together by electrical bonding force.  
      Elements & Compounds  Early chemists started studying matter and began to classify it. And they saw that certain common substances originally thought to be pure were separable into mixtures (e.g., the breathed air, which is a physical mixture of gases). Chemists separated the ‘pure’ substances from mixtures and found them to be two related but distinct types – elements and compounds. 
 h h h h h h h h      O   O   O       hOh  hOh  hOh  hOh 
 In the above you see, left  to right, atoms of the element h, Hydrogen, and atoms of element O, oxygen, and you see their combined product as molecules of the compound, hOh. Two atoms of h combine with one atom of O to form one molecule of hOh .  This shows the relationship of element and compound; the element's basic unit being the atom; and the compound's basic unit being the molecule. In the example hOh is the water molecule, whose more common chemical formula H2O signifies its molecular structure of one O atom bonded to two H, or h, atoms.  
Historical Concept of Elements: The Ancient Greek philosophers thought matter is built from one elemental substance; the first candidate was Water, then Air and later, Fire. This evolved into the idea that matter is a mix of air, earth, fire and water. By the late 1400s the qualities in a substance thought to be due to these original 4 elements began to be associated with actual elements we know today. Sulfur (S, a true chemical element) represented the quality of combustibility or fire. Mercury (Hg – from Latin, hydrargyrus, or watery silver, which the Ancients thought it), the quality of fluidity.  The differences between a mixture (separable into its parts by physical means), a chemical compound (uniform material not separable by physical means but formed by chemical combination as molecules of two or more atoms of an element), and an element were clarified in 1661 when chemist Robert Boyle recognized the fundamental atomic nature of the elements. From his experiments, he taught that an element should come from breaking down compounds into their smaller constituent parts that cannot further chemically be broken down, and in reverse, particular elements should be able to be combined to form the compound whose breakdown produced them. In 1789, chemist Antoine Lavoisier published the first list of elements from his chemical studies of decomposition and recombination following Boyle. Most were true chemical elements we know today. Seven substances that today are known to be elements - gold (Au), silver (Ag), copper (Cu), Iron (Fe), lead (Pb), tin (Sn), and mercury (Hg)  - were known to the Ancients because they are found in nature pure. Sixteen other elements were discovered in the late 1700s, with better methods of separating elements. The rest were or have since been discovered first by chemical separations then by investigations with radioactive elements and later by analysis of elements in distant stars. By year 2000, 114 elements were recognized to make the chemical compounds produced in nature or artificially by experiment. 
            Electricity   In the 1590s William Gilbert saw when amber got rubbed, it attracted other objects so ‘electricity’ got named from the Greek ‘amber’. Another 100 years passed, and two types of electricity were recognized: the charge on glass rubbed with silk, positive (+), and that on amber rubbed with wool, negative (–), each one so named because opposite and equal. When the charged amber (negative) was touched to the charged glass (positive), both charges disappeared. In 1800, Alessandro Volta, by dipping small rods one of zinc and copper, in a water solution of table salt, which made an electric current that caused a frog's leg to jerk . This showed electricity is from a chemical reaction. Also it showed the importance of electricity in the living body. Volta’s primitive batteries like today’s modern ones had each one a positive and a negative rod (terminals) that when connected in series with other batteries increased the power and whose electrical pressure differential caused electricity to flow through the connecting wires and make heat  and sparking between the terminal wires. It was guessed that electricity flowed and the flow was considered to be of particles that came to be called “electrons,” being pushed out of the negative-electricity terminal called the cathode (node of downwardness) and that these particles naturally tumbled downhill to fill an empty positive electricity terminal anode (node of emptiness). Development of the battery has progressed to today’s large storage batteries and mini long-lasting cell  batteries. The advent of the battery allowed physicist William Crookes to discover he could generate a lightning spark between a positive and a negative electrode. When Crookes placed the electrodes in a sealed glass vessel and created a vacuum within it and then turned on the switch for electricity to flow, he discovered, instead of the spark, a fluorescent glow in the wide front of the glass vessel facing the negative electrode. Crookes had invented the cathode ray vacuum tube that today is our television, video, and computer monitor screens! He published his results and by 1890 scientists were experimenting with the cathode rays from the Crookes tube.  
         X-rays and Radioactivity   On 8 November 1895 a physicist, Roentgen, shot cathode rays from his Crookes tube into a piece of metal and noted a nearby photographic paper started to glow. Even after he shielded another photographic paper with heavy cloth the cathode rays made it glow. His experiments indicated whenever he shot the ray into metal, something from the interaction between the ray and the metal penetrated the covering of the photographic paper. These were mysterious rays so he called them x-rays. Studying x-rays in magnetic and electric fields, he found that the x rays were not deflected so he guessed they carried no electric or magnetic charge. Also they were more energetic than cathode rays; they penetrated all coverings except thick Pb lead, while even a cloth-cover blocked the cathode ray electrons. Today we know these high-energy x-rays are close to the radioactive gamma (γ) rays of radium and other radioactivity. The X-rays quickly became useful for internal body imaging and Roentgen got a Nobel Prize in Physics for 1901. A year later a physicist, Antoine Becquerel, noticed the uranium he was studying caused darkening of photo plates. Prepared by knowledge of x-rays, he guessed this was another high-energy ray and his experiments showed it also to be without electric or magnetic charge. He called it “gamma ray.” His students, Marie and Pierre Curie named the process giving off the gamma ray, “radioactivity”. Madame Curie, husband Pierre, and Becquerel, got Nobel prizes in Physics for 1903. 
The Experiment that Proved the Existence of Electrons  The next step in knowledge came also with the use of the Crookes cathode ray tube. The cathode (In above figure, the smaller gray disc to your farthest right) is positioned at the narrow end of the tube. Separated but just in front of it is an anode (the larger gray disc) with small hole at its center. The vacuum tube widens into a screen (orange-yellow disc to your left) at opposite end. When the anode (+) and cathode (–) terminals are connected (turn switch on), the electric current flows and negative-charge electrons are pulled off the cathode (and, according to the Ancients, tumble down toward the positive-charge empty anode) and the central ray passes through the hole and illuminates the screen. Between the anode and the screen, note the magnet with north (N) and south (S) pole terminals facing laterally; and, at the same magnetic crossing point, also note the electric positive (+) terminal (square lavender plate below) and an electric negative (–) terminal (blue plate above) in a 90-degree rotated vertical plane crossing the magnetic field (at right angle). Four conditions of the experiment now are run.
   In B, the cathode ray tube is switched on without the magnet or the electric field turned on and a beam of electrons shoots into the anode hole.  In this case the electron beam strikes the screen, lighting the point B at center of screen without any deflection. This shows that, in absence of positive/negative electric field or North/South magnetic field, the beam of electrons is not deflected. This part of the experiment is called the control, meaning it shows the normal condition of an electron beam unaffected by electric or magnetic fields. 
In A, the electrical terminals are switched off and the magnetic field is turned on. This causes the electron beam to deflect upward to the point A on screen. This was the first proof of the close connection between electricity and magnetism. In C the magnetic field is switched off and the electric field is switched on and you note the electron beam is deflected downward away from the negative electric field charge and, since like electrical signs repel each other, it proves the beam is negative (has electrons). In the 4th part of experiment (not shown here), when the electric field and magnetic field were turned on together, the deviations of the electron beam caused by either were exactly cancelled out. It suggests that magnetism and electricity have the same absolute quantity but work in opposite direction and have opposite sign.
   From this experiment, J.J. Thomson was able to calculate the ratio of electric charge to mass for an electron (charge divided by mass) and in further experiments between 1908 and 1917 Professor R.A. Millikan was able to calculate the charge of a single electron. (By reducing the fraction in the formula, “the mass of an electron equals its charge divided by charge/mass”, and by substituting experimentally derived values, Millikan determined the mass, or absolute weight, of the single electron) Professor J.J. Thomson won a Nobel Prize in physics for 1906 after discovering the electron, and Millikan won it for 1923 after calculating its charge.
Revealing the Rays Emitted by Radioactive Elements  In the figure above, you see a radioactive substance (Imagine a radium nugget) enclosed in a Pb lead block (the metal that blocks and stops radioactive waves) with an open front to direct the radioactive rays at the (blue) screen but before reaching it the rays are subjected to an electric field that separates the ray into 3 parts, called alpha, beta and gamma rays. The alpha ray is deflected upward in the direction of the negative electric plate and the amount of deflection showed it to be a 2+ charge, later shown to be the helium ion [He2+], which is a helium atom whose 2 electrons have been knocked out of its orbital. The beta ray is deflected downward toward the +positive electric plate, and the deflection showed it to be a 1 negative charge electron (a 1– negative charge). Only the gamma ray is not deflected, showing it has no electric charge. (Other experiments show gamma rays are not affected by a magnetic field) The gamma ray gives the radioactivity.
The dangerous rays of radioactivity for human health are the gamma rays because their lack of electric charge prevents them from being deflected or neutralized in tissue targets and their high energy, like high-power bullet, allows them to deeply penetrate the body and damage underlying tissue. The other two rays, the alpha and beta rays are blocked by even the thinnest covering; also they get deflected  or neutralized by an electric charge so they dissipate in the surface layer of skin and miss the DNA of cells. 
Sub Atomic Structures - Electrons, Protons & Neutrons: By using the above-mentioned cathode ray deflection method, it was determined that a 1-minus electron charge is 1.6022x10-19 coulombs on the negative side. A 2-minus electron charge doubles that number on the negative side. By calling a proton, a 1+ charge electrical unit, we are saying its electrical charge is +1.6022x10-19 coulomb, the same quantity as an electron but in opposite, or positive, side of charge so that if a proton were to touch an electron the positive and negative charge of each would cancel out leaving a charge 0. The electron was shown to have a very tiny mass. In separate experiments, a proton weighed in at 1.67252x10-24 gram; 1,840 times heavier than the electron. 

The Neutron: The above calculations, by the 1920s, clarified the picture of the simplest atom – the hydrogen (H). It consists of a dense central nucleus that has a 1+ proton. But outside the nucleus, the hydrogen atom continues as mostly empty space with a balancing 1 minus electron in orbital. We say “orbital” instead of “orbit” because an electron is thought of not as a particle but as a wave so its orbit, in wave form, is smeared around the nucleus in an “orbital”. Measurements showed the radius of the H atom (from its center in nucleus to its outermost electron orbital) is 20,000 times the radius of its nucleus. As physicists studied the atoms that were the smallest and next smallest, of the elements, the hydrogen (H) and helium (He) atoms, they learned that the hydrogen (H) nucleus has a 1+ charge, meaning it contains 1 proton, and the helium (He) nucleus has a 2+ charge, giving it 2 protons. Because the weight of the proton is 1840 times the weight of the electron, the weight of the electron may, practically, be ignored in estimating the weight of an atom. Since the He helium has 2 protons and H hydrogen has 1, it was expected that the He atom should be twice as heavy as the H atom. But measurements showed it to be 4 times as heavy. To explain this it was guessed the He nucleus, in addition to its 2 protons, contained 2 electrically neutral particles, which were named neutrons, and are the same weight as the proton. In 1932, James Chadwick tested this idea by bombarding the metal element beryllium with alpha particles (He2+; the 2 protons in the helium nucleus with its surrounding orbital stripped of its 2 single negative-charged electrons). The alpha, being relatively massive and electrically positive were attracted by the beryllium electro-negative orbitals, collided with the nucleus in the beryllium atoms, and struck the beryllium neutrons, spinning them off like ricocheting billiard balls, and they could be identified by their emission of high-energy gamma radiation. Thus, the existence of the neutron was shown and Chadwick received a Nobel Prize for it for 1935. 
Atoms and Molecules are, respectively, the basis of Elements and Compounds: Matter has basic building blocks – the element atoms, the various combinations of which can form all chemical compounds. Each element is made up purely of its own atoms. All chemical properties that define the element are in the atom of the element. At next level, the compounds are composed purely of molecules. A molecule, like in the scissoring metaphor, is the smallest scissoring product that one could physically recognize – by color, melting point and other physical attributes – as the compound. In atomic structure, a molecule is 2 or more atoms combined by chemical bond to make the particular compound. When we talk about the smallest structure for a compound, it is the molecule. (Note that elements can exist in molecular forms, as special combinations of 2 or more same atoms, e.g., the 2-atom molecular oxygen, O2, that we breathe, or the 3-atom O3, ozone, formed by an electric discharge in oxygen gas and with the funny smell) Each element is composed of atoms all having the same number of protons in the nucleus (center of the atom) and that number is specific and unique for the single element. This number is called Atomic Number (AN). 
Atomic Structure of Atoms of the Different Elements:  The atoms have a dense, positively charged nucleus containing 1+ charged proton(s) and no-charge, same weight neutron(s) surrounded by a relatively huge space containing very light-weight negatively charged electrons around the nucleus. (The single exception is Protium, the type of hydrogen atom that has 1 proton and no neutrons and so is atomic weight 1) The electrical charge of its free atom is zero, which means that the positive charge of its proton(s) is exactly balanced by the negative charge of its electron(s). The positive charge of a nucleus comes from its protons. Practically, the weight of an atom is the sum weight of its neutrons and protons, so if we know atom H has 1 proton (normal Hydrogen with no neutron) and atom He has 2 protons plus 2 neutrons (Helium), atom, we can correctly predict that atom He is 4 times heavier than atom H. The outer sphere surrounding an atom’s nucleus contains its negative charge as the total charge of one or more electron(s). One electron is 1/1840th the mass (weight under gravity) of a proton or of a neutron. Each electron has a 1– (minus) charge and the number of electrons in the normal stable electrically neutral form of the atom is same as the atom's number of protons. 
Electrons are not points, they are Orbitals
Since the electron takes up less than 1% of this space, this outer sphere of an atom is mainly empty space. Where does it end? And where are the electrons located in it? The present view of electrons’ location in an atom is that each electron has a circular location (“orbital” rather than “orbit” because “orbit” implies a discrete body moving like a planet's orbit) a set distance from center of the atom. According to latest data, electrons are not singular bodies or particles, and so do not revolve like a point object about a center. An electron is spread out so at any one instant it has a probability of being at a point but it can not be exactly located. Also, the basic condition is an atom in its least energized resting state. When an atom becomes energized (e.g., heated up) its electrons go into wider orbitals in a quantized way; i.e., they click outward in the atom through a space-length that is an integer of the previous location (a whole number) into the new energized orbital. (Digital vs. analog)
The number of electrons in the outermost orbital of an electrically neutral atom makes the chemical properties of the element, those properties that differentiate elements.The reason for this is that these outermost orbital electrons are unstable and easily get separated from their atom (or in other case, easily attach to another atom) as 1, 2, 3 or 4 bonding points depending upon a particular atom's structural reactivity (See later section on bonding)
The number of electrons in a neutral atom is the same as its number of protons; that number, either of electrons or protons in neutral state, is its atomic number (AN), and an atom of the same element has an AN that defines the element. The AN contains useful information because it tells at a glance how many protons in the element atom nucleus and how many electrons in the orbitals of the element’s neutral atoms. For example, hearing that lithium Li has AN 3 tells it has 3 protons in its nucleus and 3 electrons in orbitals, in its neutral atom state.
Atomic Mass/Atomic Weight/Isotopes  Since a neutron and a proton are, practically, the same mass, and an electron's mass is comparatively insignificant, the mass of an atom may be estimated by counting protons and neutrons of the atom. Thus, the common form of hydrogen H, the simplest, smallest atom, has 1 proton and no neutrons and its atomic mass unit (AMU) is 1. The atom of the next larger element has 2 protons and 2 neutrons; it is helium He. Its 2 protons plus 2 neutrons give 4 AMU. The element Carbon, with 6 protons and 6 neutrons, is 12 AMU plus however many neutrons in its nucleus.
Isotopes: In each chemical element all the atoms have the same AN (atomic number). But in a sample of an element some atoms may differ in AMU. Almost all atoms in a pure sample of hydrogen gas are 1 AMU, having 1 proton and no neutron aka Protium. But a few hydrogen atoms have additionally 1 neutron, giving those atoms 2 AMU (Such a hydrogen atom is named Deuterium), and even fewer have 2 neutrons giving 3 AMU (Tritium). When an element has atoms that differ only in mass because of one or more neutrons, each is called an isotope. The isotopes (of atoms) of naturally occurring elements range from 1 to more than 10. An element's atomic mass of its main isotope will show in the whole part of its mass number; its decimal is got by averaging the other isotopes into the mix of elemental atoms according to frequency of occurrence. Thus, for hydrogen, its atomic mass of 1.008 found in charts tells us the most frequent atom of hydrogen in the naturally occurring element has 1 proton and no neutrons, AMU 1. But the .008 appended decimal is because 0.8% of hydrogen atoms (8 atoms out of 1,000) have 1 or more neutrons in the nucleus. 
What is the difference between mass and weight?  The mass of an object is the sum of its atoms' protons, neutrons and electrons in the volume of the material in the space occupied. The mass unit number is the same under all conditions and places, while the weight will vary from its mass by the acceleration of the object under influence of the gravity attraction between the object and the larger mass object on which it exists and also modified by distance from the center of mass of the larger object. To give example, my mass at this moment is the sum volumes/space occupied of all the protons, neutrons and electrons in all the atoms of my body, and, as long as I do not add or subtract to or from that, it remains the same anywhere I go. But if I get on a bathroom balance, the weight I record is based on the acceleration of my mass by the Earth’s gravity to the Earth's center at my present position on the Earth's globe. And since the attraction of gravity by a large body on a smaller body (like my body) is in proportion to the inverse square of the distance, i.e., 1/(the distance multiplied by itself) between the 2 bodies, the weight of the smaller object of given mass changes accordingly under varying masses of the attracting objects and varying distances of the weighed object from center of the mass it stands on. Thus I would weigh less on the surface of the Moon than I do on Earth because the Moon is much less massive than Earth (even though my body on the Moon’s surface would be closer to its center). I would weigh less in a jet aircraft 35,000 feet above Earth than I weigh on the ground of Earth (slightly but measurable on a fine balance) because I am further from Earth’s center of attraction in the jet than on the ground. Scientists use mass instead of weight in scientific experiments and equations. To give units of mass, scientists use the metric measurement, the gram. (Practically, the determination of mass in an experiment is based on fine balance measure in gram or its decimal) 
Avogadro’s Law and Number: the same number of elementary particles (number of atoms, molecules or ions) of any pure element or chemical compound is contained in a mass in grams equal to the element’s atomic mass unit (AMU) or the compound’s molecular weight (expressed as mass). In 1811, Avogadro, after studying the experiments of Jacques Charles and Louis Gay-Lussac, who between the 1780's and 1802 discovered that pure gases at a constant pressure expanded or contracted in direct line with the rise or drop in the temperature, arrived at this prediction, which suggests a unifying principle for all matter in the Universe. This meant to Avogadro that all pure substances contain the same number of elementary particles (atoms or molecules or ions) at a given temperature and volume. Avogadro’s prediction led to experiments that showed the number of atoms or molecules that comprised a same weight or volume unit was the same for all pure elements or pure chemical compounds. Accurate determinations of Avogadro's number became possible when American physicist Robert Millikan measured the charge on an electron. The charge on a mole of electrons is the constant called the Faraday. The best estimate of the value of a Faraday, according to the National Institute of Standards and Technology (NIST), is 96,485.3383 coulombs per mole of electrons. The best estimate of the charge on an electron based on experiments is 1.60217653 x 10-19 coulombs per electron. If you divide the charge on a mole of electrons by the charge on a single electron you obtain a value of Avogadro’s number of 6.02214154... x 1023 particles per mole. Avogadro called the unit of mass of an element or compound in grams, (a.k.a gram-molecular weight) that contains this number of elementary particles the mole or mol. It is the same number as the sum of the protons and neutrons in the atom of the elements that make up the molecule of the compound. A mole of 12C weighs 12.000 grams, a mole of pure hydrogen H is 1 gram, a mol of sodium chloride (NaCl, common table salt with molecular weight of Na 22.99 plus Cl 35.45) is 58.44 grams. And each of the mols of the different compounds or atoms contains the same Avogadro number of atoms (in the case of elements) or molecules (in the case of chemical compounds). So if we weigh a pinch-full of NaCl salt at 100 grams, we can divide the 100 by the molecular weight of NaCl (58.4) and determine that the 100 grams contains 100/58.4, or 1.7 mol of the salt. Thus by getting the metric gram weight of a compound or element on a balance, the scientist knows the mass of the object in terms of mols. A connected side fact is that, in case of all gases that are pure element or pure compound, the Avogadro’s number of unit particles are contained in the same volume (22.4 metric liters at standard temperature and pressure dry).  Avogadro’s Law gives science a handle in practical measurement. It renders knowledge of the number of protons and neutrons in the atoms of an element or the Molecular Weight number of a compound useful and practical because it allows us to quickly calculate, from the metric gram weight of a solid or metric liter volumes of a gas, the equivalent mols of elements or compounds involved in their chemical reactions. The chemical blood tests are reported by the modern SI system as mols, or decimal fractions of mols (millimols, micromoles) per liter of the blood fluid, or decimal fractions of the liter, like deciliters a tenth of a liter, or milliliters a thousandth of a liter.  
Notation for chemicals is a shortcut that shows the atoms of a compound, their proportions in it, and can show structure in 3-dimensions. For example, the molecular formula for ethyl alcohol can be C2H6O. This tells the molecule is made of carbon, hydrogen and oxygen in weight ratio 2 to 6 to 1, but a better idea of its actual structure is given by its being writ C2H5OH, which tells it is a union of 1 ethyl radical group (-C2H5) and 1 hydroxyl or alcohol radical (-OH). For even more accuracy, CH3CH2OH (Ethanol), shows the skeleton molecule, which is C-C-O-H, with carbon atoms having bonding spots for the 5 free hydrogen atoms. Even higher accuracy are formulas that show 3-dimensions as shown just below. 
(3-Dimensional) Radicals and their Notation: “Radical”, as in "ethyl radical" (–C2H5) or “methyl radical" (–CH3) or "carboxyl radical" (–COOH) or "amino radical"(–NH2) or the alcohol and ionic hydroxyl radical (–OH) are tightly bonded atoms that in chemical reactions act as a unit and are 3-dimensional. For examples, methyl chloride (CH3Cl) or ethyl alcohol (C2H5OH). You should visualize brackets about a radical, e.g., (C2H5) OH for ethyl alcohol, but, in cases where a radical reacts as single unit, the brackets are left out. However in a case where a radical is more than one unit, for example dimethyl sulfide [(CH3)2S], the brackets are put in and a subscript shows the number of methyl units – here 2 – attached to separate bonding sites (Sulfur S has two bonding sites). When writing a radical as a separate entity, a horizontal line may be attached to its bonding site atom, as with the methyl radical (–CH3) to show which atom of the radical has the open bonding site (the C atom in the CH3). In organic chemistry, a radical may undergo substitution of one or more of its single atoms to create a different radical. For example, the methyl radical CH3 in methyl alcohol (CH3OH) may have one of its H atoms substituted for by another –CH3 to become the ethyl radical in ethyl alcohol [(CH3)(CH2)OH], which is usually indicated in formula without brackets as C2H5OH.
 Writing a radical like –COOH can hide 3-D bonding features. The carboxyl, or –COOH, radical is structurally 3-D and its C atom central (The black central atom is a Carbon C in the below).

Carboxylate ion

Above: The 3D structure of the carboxyl group, often simplified to -COOH
   The –COOH has one bare bonding site notated by the –C (The black sphere) with a double-bond oxygen =O (the red bonds and spheres) that actually should be sticking out of the page at an angle and a -O-H (1+), which becomes ionic when dissolved in water. “Ionic” means, for example, that 1+ and 1–  electrically charges separate in water into a 1– (minus) ion that can be written (O=C–O) and is called “carboxyl ion” and a 1+ ion, H+, the hydrogen ion. But what is an “ion”?
Ions & Ionic Compounds: In describing the structure of an atom, we have stated its electro-neutrality (e.g., the 1+ proton in an H nucleus is balanced by a 1-minus charge electron in its atom's orbital). The proton number in an atom is very stable (i.e., number of protons in a particular element's atomic nucleus is the Atomic Number and defines an atom as being of a particular element) but the electrons exist in orbitals and some are not stable. The force that holds electrons in orbitals is the positive electrical field from the proton in the atom's nucleus. In electricity, opposites attract. But the attracting electro-positive force in a nucleus varies with size and charge in the nucleus and with location distance from the nucleus to the electron orbitals. The nucleus in large atoms exerts a more powerful pull on an equal-distanced electron than the nucleus in smaller atoms; and the pull weakens, the further out the electron's orbital is from the nucleus.
   Electron orbitals are in shells at varying distances from a nucleus. The outermost orbital electrons are less stable than the inner electrons because the outermost are more weakly attracted to the more inwardly distant, positive nucleus; so the outermost electrons, especially the electrons 1, 2 and 3, tend to get easily detached in atoms of that set of elements. On the other hand another set of element atom that lacks 1, 2 or 3 outermost electrons to fill an outer orbital tends to attract and acquire them. When an atom loses 1 or more electrons from its orbital, its electric charge becomes unbalanced in the positive direction. For example, the electrically neutral hydrogen atom H has 1 proton in its nucleus and 1 electron in its orbital. It tends to lose the electron and then it acquires a 1+ electrical charge and we indicate this by the H+.  When an atom loses or gains electrons and becomes charged, we call it an ion.  Positively charged ions, like H+, when they are placed in an electrical field migrate toward the negative terminal, or cathode because opposite charges attract. So a positive ion is also called cationAtoms that gain electrons become negatively charged. For example, fluorine F as neutral atom normally has 9 protons and 9 electrons but it tends to gain 1 electron in its outer orbital and, when it does, it becomes the fluorine ion (fluoride) with a 1-minus electric charge, written F. Negative ions are called anions (i.e., they are attracted to positive terminal, anode). Atoms like hydrogen H, beryllium Be and boron B, which have respectively 1, 2 and 3 electron(s) in outermost orbital, tend to lose these electron(s) easily, i.e., they are electron-donors. Thus H hydrogen  loses a 1-negative electron and becomes the H+ion, the Be beryllium loses two 1-negative charge electrons and becomes the Be2+ ion, and the B boron loses its three 1-negative charge electrons and becomes the B3+ ion. (All 3 are cations) But atoms of elements that lack 1, 2, or 3 electrons to fill their outermost orbital shell tend to pick up electrons easily and become similar-number charge negative ions (e.g., oxygen lacks 2 electrons so O plus two 1-negative charge electrons becomes O2- ion). These are mostly gas elements like O oxygen, N nitrogen, F fluorine and Cl chlorine. Note here a principle: atoms tend toward a complete set of orbital electrons in the atom's outer shell. This explains the formation of ions. 
Ions are important in living chemistry. First, they exist in compounds, like salts (Na+Cl), acids (H+ compounds) and bases (OH compounds), which are the stuff of life. Second, they are sources of body electricity, which is the flow of electrons coming from atoms that have become ions. In body fluids, ions serve important electrical transmission functions and are called “electrolyte” (e.g., the electrolytes sodium Na+, potassium K+, calcium Ca++, chloride, Cl, bicarbonate HCO3). Ions are formed in chemical reactions. An element whose neutral atoms are electron donors (e.g., Na sodium) mixes with an element whose neutral atoms are electron acceptors (e.g., Cl chlorine), forming the ionic compound Na+Cl, sodium chloride table salt. 
Ionic compounds, like Na+Cl-, in absence of water, tend to form crystal solids, and one mol, or 58.44 grams of NaCl, contains the Avogadro number c.6.022 x 1023 molecules of NaCl in its crystal structure. Note that an ionic compound like Na+Cl- in dry crystal form is electrically neutral because each 1+ Na+ is neutralized by 1-negative Cl-. But as soon as an ionic compound is in water, it liberates separate Na+ and Cl- ions (electrolytes) into the water solution. Pure distilled water, because it has no ions, will not pass electric current. But water in which a small amount of ionic compound is dissolved gets positive and negative ions and conducts as in the famous high-school science experiment where an electric bulb lights up when salt is put into the water that forms the conductor of electricity to the bulb. 
Organic and Inorganic; Naming Compounds: Organic (associated with life) compounds contain carbon (C), usually in combinations of elements such as hydrogen (H), oxygen (O), nitrogen (N), sulfur (S) and phosphorus (P). The other compounds are inorganic (associated with non-life). Among common organic carbon C compounds are the poison gas carbon monoxide (CO), and the global warmers, carbon dioxide (CO2)  and  CH4 methane; and also compounds containing cyanide (CN-), carbonate (CO32-) and bicarbonate (HCO3-). Organic compounds may be ionic (positive and negative electric charge), which may be acids (release H+) or bases (OH-). Or they may be molecular (No electric charge) like cholesterol. 
Ionic Compounds: Most are binary, i.e., compounds formed of 2 elements in ionic form. For naming binary compounds, first comes the metal element (cation, name for negative charged ion, pronounced cat-ai-yon) followed by the gas element (anion, positively charged ion, pronounced an-ai-yon) partner with changed ending. Thus NaCl (common table salt) is named sodium chloride (from the Cl chlorine). The usually indicated positive (+) and negative (–) charges on cation and anion are not shown in the formula NaCl because each has neutralized the other. The “-ide” ending is also used for certain anion groups (the radicals) containing other elemental atoms, such as hydroxide (OH-) and cyanide (CN-). Thus, compounds LiOH and KCN are named lithium hydroxide and potassium cyanide. An “-ate” ending is used for anion groups that have, additional oxygen, e.g., “carbonate” (CO32–) and “bicarbonate” (HCO3); the last formula also demonstrates the use of “bi-” prefix when H+ ion reduces charge as CO32– + H+  = HCO3.  Solid ionic compounds are electrically neutral. This means that the sum of charges on cation and anion in each formula unit must add up to zero (Zero sum). So the formula for a compound must be balanced, i.e., the number of atoms multiplied by the charge of its ion on the cation side must equal the number of atoms multiplied by the charge of its anion on the anion side. Some examples, illustrate. Sodium chloride: Na+ + Cl- = NaCl  ([1+] + [1-] = 0); Zinc Iodide: Zn2+ + 2I- = ZnI2 ([2+] + [2x1-] = 0); Barium Sulfide: Ba2+ + S2- =  BaS ([2+] + [2-]=0), both subscripts divisible, so reduce to smallest ratio, Ba2S2 as BaS; and Aluminum oxide: Al3+ + O2  Al2O3 ([2x3+]= [3x2-] =0). Certain metals can form more than one charge number cation. Iron, depending on conditions, can lose either 2 or 3 electrons to form the cations Fe2+ or Fe3+.  In an older system the (2+) charge took the suffix, “ous” and the (3+) charge took the suffix, “-ic”, e.g., Fe2+ give “ferrous chloride” FeCl2, and, “ferric chloride” FeCl3. It is a simple system and you should know it because many compound names still use it, but, today, the preferred system is for Roman numerals to show ion charge number. Thus FeCl2 is iron (II) chloride, and FeCl3, is iron (III) chloride.
So-called "molecular" compounds are non-ionic, i.e., they do not consist of or do not split into cations and anions. They exist as inorganic gases and organic carbon, hydrogen and oxygen solid compounds like carbon dioxide or cholesterol. As inorganic gases, their naming is same as with ionic compounds. So HCl (in water it is molecular “hydrochloric acid") is hydrogen chloride; HBr, hydrogen bromide; SiC, silicon carbide.  Some peculiarities in naming come about because pairs of elements may form more than one compound where a same atom is represented 1, 2, 3 or more times. So CO is carbon monoxide; CO2, carbon dioxide, N2O4, dinitrogen tetroxide, etc. Here, Greek prefixes for 1 – mono-, 2 – di, 3 – tri, 4 – tetra are used. Often,“mono-" is omitted for a first element, as in SO2, sulfur dioxide, the one sulfur atom being understood in absence of prefix. An exception to Greek prefixes involves molecular compounds containing H, hydrogen. Traditionally these have their historic names, e.g., CH4 is methane; NH3, ammonia; H2O, water.  
Cyclic Molecules and their Radicals: So far in describing the molecules and the structure of chemical compounds, they have all been linear (like the carbon core compounds –C–C–C–C–). However the most important organic compounds are cyclic, with the C atoms forming a geometric polygon ring – a hexagon or pentagon. A famous example, inorganic, is the smelly solvent benzene. View its variously written structure:
 Note, benzene is a 6-carbon hexagon, the C’s bond to each other to form the hexagon and the H’s jut out on the outer C bonding sites. Note the two structures, above to your left, where no letters C or H are shown. When one or more of the hydrogen's H’s detaches from the ring molecule, it gives types of radicals with bare bonding sites where the detached H atoms were; radicals that can combine with other atoms or radicals to form new compounds. Note the C’s show bonding to each other by alternating single –– and double-bar = lines. The single line indicates a single site bonding on the C atom. You will learn in the chapter on Lipids that double bond C’s (–C=C–) are considered a state of “unsaturation” of C bonding because the double bond (=) leaves one less H atom to bond on the C than a single bond. Thus unsaturated fats or, slang “unsat fat”! Below on your right see a similar cyclic hexagon structure as benzene, without the double bonds,Note the suffixes “-ene” (Benzene)  and “-ane” (Cyclohexane).  The -ene indicates a structure has 1 or more double-bonds. The -ane) means no double bonds at all, ie, a saturated hydrocarbon nutrient as in sat fats. And note that “Benzene” is a traditional name for what also could be named Cyclohexene (cf. Cyclohexane, eg, a 6-sided, or hexagon of C atoms with degree of unsaturation indicated by the -ene or saturation by the -ane suffixes).
Electron Sharing in Chemical Bonds  The formation of molecules depends on the chemical bonds between the atoms that form the molecules. These bonds are shown here by lines between atoms, for example, as in H–H to show one H-atom bonded to another to make the molecule of hydrogen gas, whose shortcut is more commonly writ H2. Another shortcut to replace lines for bonding is proximity as when writing CH4 for the methane molecule instead of the bulkier but more accurate  C with an H at 0, 90, 180, and 270-degree positions. Bonding is the basis of attraction between atoms and its power comes from electron-sharing. For an explanatory example, look at hydrogen gas, which molecularly can be written H–H. Recall that H, as its atomic number 1 tells, is the simplest atom with a single 1+ electric-charge proton in its nucleus balanced by a single 1-negative (1-minus) electric-charge electron in its single shell orbital. The hydrogen atom as a singlet H1 does not exist free in the natural state on Earth because H hydrogen can be said to have an overwhelming inanimate desire to have a full complement of at least 2 electrons in its single electron shell. The next atomic number element, He helium, already has 2 electrons in its neutral atom so it is satisfied, but H hydrogen only has one electron so under normal energy conditions the singlet H atoms bond together to share each one's single electron and thus the combination forms H-H, or H2 molecules of hydrogen gas. In other words, the hydrogen H atom which has a single electron shell incompletely filled by one electron yearns mightily to be like its next higher element, helium He, in having the full complement of 2 electrons in its single inner electron shell. So each H atom is attracted and bonds to its neighbor H atom to form the (H-H), or the H2, molecule in which by sharing each one’s electron, each H atom completes its 2-electron inner orbital shell and is very satisfied. This can be pictured by an H,(or, turned around a H)  with the hollow dot representing the yearning electron. So an H∘ and another ∘H yearn mightily for each other and become bonded, and the bonding is shown by H∘∘H, or we write H:H. or H-H or H2.
   Note I use the simplest atom, the H, but a similar explanation goes for other element atoms to form atom bonds. (In the larger element atoms the outer electron shell has space for 8 or more even-number electrons instead of the 2 seen with H and He atoms, but the principle of "yearning to fill the partly empty shell" is the same) Double bonds like –C=C–, and triple bonds –CC are cases of electron pair sharing seen in the unsaturated fats. In these cases, each line of the double or triple bond represents a shared electron pair. And note that a double or triple shared electron pairing is a shortcut in bonding, so in the double bond –C=C–  the C atoms involved in bonding are not utilizing the full bonding potential of their outer electrons, and thus leave one or more of the electrons to react to form other bonds. So double- or triple-bonded carbon compounds are said to be "unsaturated" because they do not use up all the bonding power of their carbon electrons. And these unsaturated compounds are thus highly reactive and unstable. (And unhealthy in your body)
 Chemical energy is stored within the structure of chemical compounds in the bonds. When substances participate in chemical reactions, chemical energy may be released as heat if the bonds get released or it may power other chemical reactions.
   Your body uses chemical-bond energy storage in parceling out energy units as though the units are money currency. It does this by storing energy in a special high-energy bond chemical, adenosine triphosphate, or ATP, that acts like an energy credit card by an enzyme causing the release of its high-energy phosphate-bond and in so doing releasing a set amount of energy in a packet for metabolic work. (Adenosine TriPhosphate under enzyme effect breaks one bond to become Adenosine DiPhosphate + 1 released phosphate energy unit that is used for metabolic work inside cells) This is one of the most important facts of body energy metabolism, as we shall see in the carbohydrate section and other later sections so do not forget ATP to ADP plus body energy packet.  Also the phosphate bond in ATP is used in many other phosphates for energy transfer and storage.         
Chemical Equations use symbols to show what happens during a chemical reaction and the amount of chemical substances involved in the reaction. Consider hydrogen gas as molecules of hydrogen (H2) combining with molecules of oxygen (O2) to form water (H20), the chemical reaction written  (2H2 + O2  --> 2H2O.
On your left of the arrow are reactants and on right, product. An arrow indicating one direction shows that, normally, energy-release favors the reaction in that direction; here, to run to the production of water. The reverse reaction would require input of energy, eg, an electric current run through water would dissociate water molecules to hydrogen and oxygen gas. Most often there are two opposite arrows meaning the reaction goes both ways under usual conditions to equilibrium point. In chemical equations, the subscripts indicate the number of atoms of chemical element or of radical group of elements in each molecule. The large front numbers indicate the proportion of molecules  involved in the reaction. (The number "1" is  understood and not notated) In the "2H2 + O2  ---> 2H2O", we see 2 molecules of hydrogen gas and 1 molecule of oxygen gas combine to form 2 molecules of water. This is an exact molar reaction and if you weigh the reactants and products, you will discover that (4 x 1.008), or 4.032 grams hydrogen gas, and (2 x 15.999), or 31.998 grams oxygen gas formed (2 x 18.015), or 36.03 grams water.
An enzyme is a chemical that speeds the rate of a chemical reaction without itself getting used up. Many vitamins are enzymes and many minerals form the core of enzyme structure. (Cobalt forms the core of vitamin B12; magnesium forms the core of chlorophyll) A more general name for enzyme is chemical catalyst.
A most famous enzyme chlorophyll-speeded reaction is shown just below: the famous photosynthesis.
In the equation you see the photosynthesis reaction that occurs in leaf exposed to sunlight: 6 moles of atmospheric carbon dioxide gas combine with 6 moles of water in the presence of the green pigment catalyst (enzyme) chlorophyll, which captures sun ray energy to speed the reaction that forms 1 mole of 6-carbon sugar and 6 moles of oxygen liberated as the gas O2 into Earth’s atmosphere. Here we see a catalyst chemical reaction that explains life on earth; and also we see the protective affect of plants against the Global Warming greenhouse effect, by removing the carbon dioxide. 
Aqueous Solution, Concentration, Acid/Base  
A solution is a mixture of particles (chemical compounds, molecules or ions called the solute) dissolved in fluid (the solvent). The solute-dissolved solution may be electrolyte or non-electrolyte. Electrolyte solute in water liberates ions (e.g., NaCl sodium chloride in water liberates Na+ and Cl ions) so inorganic salts like NaCl become electrolytes in water. Organic compounds (CHO compounds of life) are often non-electrolytes. Weak electrolytes do not completely ionize in solution. Acetic acid (5% solution is vinegar) is one. Its dissociation in water is incomplete as follows: CH3COOH  CH3COO-(acetate anion in water) + H+ (hydrogen {cat}ion in water). Acetic acid is an acid because it liberates H+ in aqueous (water) solution. 
 The Hydration Process: What happens when solid crystal salt (NaCl) is dropped into water (H2O) and seemingly disappears? That it has not really disappeared can be shown; because pure distilled water, before it mixes with NaCl is non-electrolyte so it will not pass electric current, but once even a little NaCl dissolves in it, the electrolytes Na+ and Cl will pass a current and serve, like metal wire, to light a bulb connected in series between positive and negative terminals of a battery.
   Water is an effective solvent for ionic compounds. Why? Consider 10 cubic centimeters (cc) of distilled water (pure with no solute in it). I choose 10 cc of water because 1 cc of water is 1 gram, so 10 cc is 10 grams. And the molecular weight of water, H2O, is 10 AMU  (The two H atoms = 2 and the one O = 8) so ten grams water is 1 mol of water and contains the Avogadro number (c.6.02x1023) of molecules H2O. And although these H2O molecules are electrically neutral in pure solution, a consideration of the asymmetric shape of the HO water molecule
shows 2 separated electric single-positive (H+) jutting-out points balanced against 1 electric double-negative (O2-) corner right angle point. Such a molecule with uneven electric charge distribution is called a polar molecule because it contains separated poles of electro-negative and -positive. And such molecules are good solvents for ionic compounds because, when an ionic compound such as NaCl dissolves in H2O, the 3-D network of ions in its solid state is scrambled, and the Na+ and Clions get separated from each other because the Na+ ions are attracted to the electronegative –O2– point of the H2O molecules, and the Cl ions are attracted to one of its H+ positive points, preventing each Na+ and Cl from neutralizing the other as in the solid. 
Acids & Bases: An acid releases H+ in solution: it is sour like lemon (citric acid, aspirin) and causes color change with dye (famous litmus test, red for acid, blue for base). Acids release H2 hydrogen gas when metals like Zn, Mg or Fe are immersed in them, e.g., 2HCl (aqua) + Mg (solid) becomes MgCl2 (aq) + H2 (gas); and acids react with bicarbonates to produce carbon dioxide gas, [HCl (aq) + NaHCO3 (bicarb) becomes NaCl (aq, salt) + H2O (l) + CO2 (bubbles of soda)]. A base (a.k.a. alkali, alkaline; most frequently OH- ion) tastes bitter; feels slippery (soaps are alkaline), and turns litmus blue; opposite to acid. The overall state of body acidity expressed as pH number (See later) is important in good health, like body temperature, blood pressure and heart rate.
The Concentrations of Solutions: The concentrations of chemical substances in body fluids like blood or urine are reported in milligrams per unit volume in USA, usually per liter (L) or deciliter (dL, 0.1 L) or milliliter (mL, 0.001L, or cubic centimeter, cc). The milligram we already know as 1/1000 of a gram. The Mol is the gram molecular weight, in grams number, of a compound. A mol of any compound contains the weight in grams of that the atoms of the  chemical compound add up to, and contains Avogadro’s number of molecules of that compound (or ions for ionic solutions). Mol per liter is used for giving concentrations of substance in blood in most countries other than USA, and the use of mol instead of gram is part of SI, or System International. The metric prefixes deci (1/10), centi (1/100), milli (1/1000), micro (1/1,000,000), nano (1/1,000,000,000) and pico (1/1,000,000,000,000) are appended to units as called for by the respectively lower concentrations. In USA and a few other countries the concentration is given in milligrams or deciliter fractions thereof.
 The 3 States of Matter as well as TemperatureEvery pure substance can exist physically as solid, liquid or gas. Water can be solid ice, liquid water, or steam gas. It changes from solid to liquid to gas with rise in temperature or lowering in atmosphere pressure.
The temperature units: The older generation, Centigrade,measure was based on the point where ice melts to water, which got numbered zero degree (0 C) and each 1 C measurement was graduated in 100 parts to 100 C where water boils to steam. Since the Centigrade unit has been replaced by the presently used Celsius unit, the actual basis of the zero degree point is now the so called “triple point” where purified water under very low pressure exists together, at one instant, as ice, liquid and gas, and it is most close to 0.01 C; but, practically, no different from the older Centigrade definition. Each Celsius degree is a degree in the Kelvin temperature scale, which is based on an absolute zero temperature, being the point where all molecular movement would cease, which is numbered and called zero Kelvin (0 K), or in Celsius number, minus 273.15 C. (Note, when temperature is expressed as Kelvin, no degree superscript need be used) So in converting Celsius (C) to Kelvin, just add 273.15 K units to the Celsius unit. The Fahrenheit unit is an older system still used in USA.  Celsius = (Fahrenheit minus 32) multiplied by 5/9, and, in reverse, Fahrenheit = 9/5 (Celsius) + 32. 
Note that boiling water 100C = 212 degrees Fahrenheit, and that 11 degrees Fahrenheit = minus 11 degrees Celsius  and that minus 40 Fahrenheit = minus 40 Celsius. And, of course, freezing ice water 0C is 32 degrees Fahrenheit.
The state of a substance is determined by the temperature and pressure affecting the closeness of its molecules. With solids, the molecules are packed tightly in orderly fashion; thus giving solidity of form, rigidity, and strength, as with solid metals. As temperature increases and/or atmosphere pressure decreases, the substance particles become more energetic and less pressed and cannot be held together so they begin to slide over each other and we have the fluidity of water. As heat keeps being increased (or pressure keeps being decreased), the energy imparted to the fluid particles becomes so great that the particles fly out of control and become formless gas. Each element or compound has melting/freezing and boiling/liquefaction point at given air pressure and temperature, differing from other elements due to the varying attraction of the different molecules. This, in turn is based on the molecules' atomic or ionic structure. One mole of a pure substance (compound or element) gas at standard atmosphere temperature and pressure has 22.4 liters volume. 
About Gases & Atmospheric Pressure   You may have already run across: “under STPD”, the acronym for sea-level, temperature (0 Celsius) and pressure (760 mm of Hg column) dry (air humidity). Here are facts about gas pressure. Note that our atmosphere, the air we breathe on Earth’s surface, is a physical mixture of chemical element gases and chemical compound gases. (Each one separable by physical methods like centrifuging or freezing) About 78% of our air is nitrogen (N2; note the element nitrogen N in its bi-atomic molecular form), 21% is oxygen (O2), and the remaining 1% is a mix of carbon dioxide (CO2), methane (CH4), the oxides of nitrogen, and the inert element gases like helium (He) and Neon (Ne). The molecules in the atmosphere, like those of all other matter, are pulled down by Earth's gravity so the air is denser near the surface than at high altitude. That is why the air outside the pressurized cabin of a passenger jet is too thin to breathe comfortably. The denser the atmosphere, the more pressure its molecules exert on exposed surfaces. The force we experience exposed to Earth atmosphere on its surface equals the weight of the air above us. The pressure exerted by this air at sea level is what is meant by sea level pressure, the S and P of the STPD. Its number depends on temperature and weather conditions, and on location. All other things equal, atmospheric pressure is higher below sea level (Death Valley, California) than 1 mile above (Denver, Colorado) and in cold than warm. A barometer measures atmospheric pressure. It is a transparent tube of small standard diameter filled with mercury (Hg) in a column that can be measured by the level line of the mercury Hg in the tube. The mercury fills the tube except for a small space at top, which is a relative vacuum. The atmospheric air transmits its weight through the air to the column of mercury, which rises into the vacuum at top and finds a height in millimeters of Hg of the atmospheric pressure. At sea level and at air temperature 0C the dry air atmospheric pressure measures 760 mm Hg, the standard for sea level. The unit 1 mm Hg is 1 torr. (After Evangelista Torricelli) 
Energy, Waves, EMG Radiation & Spectrum
      Energy is also expressed as wave motion.
Waves and their Properties: We know water waves from ocean or from throwing a pebble onto a quiet surface of a pond. The wave has peak and a valley and comes in series, one following another. Think of a wave vibrating up and down like a plucked string of guitar.Electromagnetic (EMG) Waves in 3 Dimensions: Note the lavender electric field and green magnetic field at 90-degrees to each other. 
In electromagnetic (EMG) waves, the electric field and the magnetic field each have the same wavelength, frequency and amplitude but each one vibrates in a plane at right angles to the other. The EMG waves shown in the figure are moving forward from your left to right like an arrow released from a bow; the speed determined by the energy from the force applied to start it moving; its speed affected by the medium transmitting the wave (air, water, or lack of medium as in a vacuum). The wavelength is the length measurement (in nanometers, or 1 billionth of a meter or c.1/3rd billionth of a foot) between wave peaks. The velocity, or speed at which a wave peak travels – called frequency or f,  is measured in cycles per second (A cycle is a full wave that includes its down amplitude and its up amplitude and is measured along the horizontal axis) and is given in the unit, hertz. (Hz; 1 Hz = 1 cycle per second, or 60 wave peaks passing in 1 minute) The amplitude is the maximal distance of the wave peak from the central baseline (the height of the wave peak tip above baseline). Now, consider an ocean wave? We see it because the water surface is an interface between 2 mediums – air and water – and the air permits us to see the wave peaks and valleys. The wavelength, wave frequency and wave amplitude are all easily observed and measured in units of our real life in water waves. Speed of transmission is rather slow, 30 to 50 feet (c.9-15 meters) a minute. If we consider a water wave, we understand it as compression and relaxation on the water molecules; the max. compression being in the wave peaks and the max. relaxation in the wave troughs. In waves from a pebble dropped onto a pond, the potential energy from gravity is transmitted to the surface of the pond and produces vibration of the pond-water molecules that propagates as the waves. The waves originate in an energetic force applied at the wave source. Ocean waves are caused by forces exerted on oceans by Earth’s rotation about its axis combined with the pulls of Moon and Sun on the Earth as it moves around the Sun. The solid parts of the Earth cannot move much, but the liquid seas are dragged back and forth by the combined forces and the result is the tides and waves. Think about barriers to water waves. Solid steel or a cement dam stops them, but a sieve does not completely stop them. Molecules are transmitting the waves and if there are wide enough openings in a barrier, the wave continues, but if the substance of the barrier is compact so that the openings are smaller than a wave’s amplitude, a block will occur.
   Similarly, sound waves are alternating compression and relaxation on molecules in air set up by a force applied at the wave source. The waves travel in all directions out from the source of the force that creates them. That the speed of a wave varies with the medium it passes through is evident with sound. Its speed in wire is faster than in air. The loudness of the sound we hear is from the amplitude of its waves. Frequency and amplitude of sound waves are important for human hearing. Lower than 20 cycles per second (Hertz) and higher than 20,000 (20 KHz) are outside our range of hearing. Sound waves >20,000 cycles/second are ultrasound range and used in radar and medical body imaging. Amplitude makes the loudness of heard sound. Sound waves are harder to block than water waves; they travel at a smaller amplitude so each wave takes up less space and can be less easily blocked by materials. Sound waves also go around wall segments. High-pitched sound waves are those with smaller wavelength and higher frequencies, i.e., more energetic and thus harder to block.    

            ELECTROMAGNETIC WAVES (EMG)The Figure shows the range of  electromagnetic wave energy. In the top schematic, on your extreme left, is the highest energy radiation, which has the smallest wavelengths (nm=nanometers, 1 billionth of a meter) and highest frequencies (1020 Hz wave peaks in 1 sec.). It is the gamma (γ)ray of radioactivity. Then, moving to your right is the slightly less but still highly energetic x-ray. With the visible light spectrum, note the colors that give the mnemonic ROY G. BIV used for memorizing by students. It is a part of our Sun’s EMG wave radiation energy. On the edges of  the spectrum of visible light, to your left is the ultraviolet used in tanning, and to your right is the infra-red, which is the hottest heat wave in a heating lamp. Continuing higher in wavelength, the microwaves of ovens, then radio waves and longer wavelengths. 
Electromagnetic (EMG) Waves resemble water and sound waves of air in that they have wavelength, frequency and amplitude but EMG waves differ by producing electrical and magnetic fields that vibrate at 900 to each other. Also EMG measurements differ by orders of magnitude. The most energetic EMG waves have shortest wavelength and highest frequency (Wave peaks per second). The EMG waves move at 2.99792458 x 108 meters per second in vacuum; it varies slightly in different media, and is rounded to 3.00 and expressed as 300,000 km/sec or 186,000 miles/sec. This is the famous speed of light that Einstein’s Theory of Special Relativity says can never be surpassed. The speed of light in a near vacuum is known and constant; the wavelength may be computed by the speed of light multiplied by the frequency, and in reverse the frequency computes by wavelength divided by the speed of light. Note the wide range of wavelengths, and see the color spectrum where visible light is located and note infrared >700 and ultraviolet < 400 nanometers wavelength. 
Danger of EMG Waves  The term "radiation" carries an idea of danger to life. It is a vague word when used alone. The EMG waves are dangerous to life to the extent they have very short wavelengths/very high frequencies. These can be called high energy or ionizing radiation because their high energy penetrates living tissue and strikes the atoms and molecules of our vital organs knocking out electrons and producing ions, and the ions damage or kill the cells. A useful rule of thumb for dangerous radiation is wavelengths shorter than visible light - to your left of the visible light spectrum shown above. This starts with the ultraviolet sun's rays (Skin tanning cancer), then goes to x-rays, gamma radiation and cosmic rays - all very dangerous. And note that infra red heating lamps and microwaves, the latter often worried about in cell phones and cooking, are to the right of the visible light spectrum and have the sole risk of burns from the heat applied closeup.
  Chapter 6 Continues in next Section c. To read now, click 2.6c Electron Arrangement in Atoms/Quantum/Lase

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