Thursday, September 23, 2010

2.6b Essential Physical Science

Physician's Notebooks 2  - http://physiciansnotebook.blogspot.com - See Homepage    
Update 26 Sept. 2014  Reading the following sections may increase your scores on tests - SAT, MCAT, TOEFL, IQ - and get you a free or low-cost education scholarship. 
2.6b: Intro to Chemistry & Physics - Structure of Matter:  This section gives the science essential for success in our modern world.  Best read in small sections. Below are the the small sections in order as each appears. To read each separately, use search & find or scroll down 
.Matter - What is it and what is it not? 
The Atomic Theory 
Elements & Compounds 
Electricity
 X-rays and Radioactivity 
Sub Atomic Structures - Electrons, Protons & Neutrons 
Atoms & Molecules are Basics in the Elements & 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  
Molecular Chemical Formulas/Radicals/Ions/Reactions 
Ions & Ionic Compounds  
Naming Chemical 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?  To be happy and successful in life you need to know yourself – how you are madcarboxe and function. Start by learning about theUniverse we all exist in because you are one of the things that make up Universe. And since Universe is made of matter, let’s start on the structure of matter. It has been taught that 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 or 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 still thousands of atoms. But vacuum space has an important relation to matter because matter is composed of basic particles – molecules, atoms and subatomic like electrons - 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 learning we 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 the water as steam).  
        The Atomic Theory   The idea that matter is made of basic particles with the smallest particles being atoms goes back to the Ancient Greeks. The original meaning of atom (from the Greek, indivisible) implies a unit of matter that cannot be reduced further. Imagine you have a magic scissor that can cut an object in two, down to subatomic level. You take an ingot of pure 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 that 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 see 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 makes 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 and opened the gates of human imagination to a concept that matter is discontinuous (i.e., matter is not the smooth material it appears but rather a structure of units separated by empty space).The Ancient Greeks could not test the idea; and it would take till the 1800's to develop The Atomic Theory, which is:1) All matter is made up of combinations of the purest substances called elements.2) Each 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 pure substances that are chemical combinations of the elements. These mixtures 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. 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 classifying it. And they saw that certain common substances, originally thought to be pure, were separable into mixtures (e.g., the breathed air, a physical mixture of gases). Chemists separated the ‘pure’ substances from mixtures and found the substances 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 atoms of the element h Hydrogen (small h is used for contrast with large O) and atoms of element O oxygen, and you see their combined product as molecules of compound hOh . Two atoms of h combine with one atom of O to form one molecule hOh .  This shows the relationship of element and compound; the element's basic unit being the atom; and the compound's being the molecule. In the example hOh is water, whose chemical formula H2O is its molecule structure of one O atom bonded to two H atoms.  
Historical Concept of Elements: The Ancient Greeks thought matter is built from one elemental substance; the first candidate, Water, then Air and later, Fire. This evolved into the idea that matter is the mix of air, earth, fire and water.By the late 1400's the qualities in a substance thought to be due to the original 4 elements began to be associated with actual elements we know today.Sulfur (S, a true 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 English chemist Robert Boyle recognized the fundamental nature of the elements. From his experiments, he taught an element should come from breaking down compounds into smaller 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 and he was able to prove the error of the Ancient Greek’s idea that everything is made of air, earth, fire and water.  In 1789 French chemist Antoine Lavoisier published the first list of elements from his chemical studies of decomposition and recombination following Boyle. Most were true 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 1700's, with better methods of separating elements. The rest were 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 and artificially by experiment. 
            Electricity   In the 1590's William Gilbert saw that when amber got rubbed, it attracted other objects so ‘electric(ity)’ is named after 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 (–), so designated because opposite and equal.  When the charged amber (negative) was touched to the charged glass (positive), both charges disappeared.  In 1800, the Italian, Alessandro Volta, by dipping small rods, one of zinc, the other, copper, in a water solution of table salt, 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 electric power and whose electrical pressure differential caused electricity to flow through the connecting wire and make sparks between the terminal wires.  It was guessed that electricity flowed and the flow was considered to be of particles, which 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).  Development of the battery has progressed to today’s large storage batteries.  The advent of the battery allowed British physicist William Crookes to discover he could generate a large 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 a 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   A physicist, Roentgen, shot the cathode ray into many different substances and materials. On 8 November 1895 he 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 electrons from the cathode rays did not penetrate and darken photographic paper but whenever he shot the ray into metal, something from the interaction between the ray and the metal penetrated the covering of the photographic paper. He guessed 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.   X-rays quickly became useful for internal body imaging and Roentgen got a Nobel Prize in Physics for 1901.  A year later a physicist in Paris, Antoine Becquerel, noticed the uranium ore 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 rays.” His students, Marie and Pierre Curie named the process giving off the gamma rays, “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 on 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, like a TV screen. When the anode (+) and cathode (–) terminals are connected by switching-on and the circuit is completed in the battery, the electrons are pulled off the cathode toward the anode and pass through the hole and illuminate the TV screen at point B (the central point on the orange-yellow disc screen).Between the anode and the screen is a magnet with north (N) and south (S) pole terminals facing so that the magnetic field between N and S crosses the beam of electrons at right angle in a horizontal plane. At same crossing point is an electric positive (+) terminal (square lavender plate below) and an electric negative (–) terminal (blue plate above) in a vertical plane also crossing the electron beam at right angle.  Four conditions of the experiment are run.
In B, the cathode ray tube is switched on and a beam of electrons shoots into the anode hole without the magnet or the electric field turned on. 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 C, the electrical terminals are activated creating an electric field but the magnet is not turned on so there is no magnetic field. In this case, the electron beam is deflected downward to point C on screen. Since it is being deflected away from the negative terminal it proves electrons have a negative electrical charge because like-charge repels like-charge. (Or, given that, it proves electrons are the ray) The experiment proves the electric negativity of the electron.  In A, the electrical terminals are switched off and the magnetic field is turned on. This causes the electron beam to deflect upward to point A on screen. This was the first proof of the close connection between electricity and magnetism.In the 4th part of experiment (not shown), 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 by 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 (weight) of the single electron. Professor J.J. Thomson won a Nobel Prize in physics for 1906 for discovering the electron, and Millikan won it for 1923 for calculating its charge.
Revealing the Rays Emitted by Radioactive Elements             In the figure just above, you see a radioactive substance (Imagine a radium nugget) enclosed in a lead block (the metal that stops radioactive waves) with an open front to direct the radioactive rays at a (blue) screen but before reaching it the rays are subjected to an electric field that separates the ray into 3 parts, the 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 particle, later shown to be the helium ion [He2+], a helium atom whose 2 electrons have been knocked out of orbital. The βray is deflected downward toward the +positive electric plate, and the deflection showed it to be the 1– (one minus) electron. Only the gamma ray is not deflected, showing it has no electric charge. The gamma ray gives the radioactivity. The experiment shows a property of radioactivity: the emission of gamma rays.
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 α- and β-rays are blocked by even the thinnest covering; also they get deflected by a like electric charge so they dissipate in the surface layer of skin or miss the DNA of cells. 
Sub Atomic Structures - Electrons, Protons & Neutrons  Electrons and Protons: By using the cathode ray deflection method, it was determined that a 1-minus electron charge 1.6022x10-19 coulombs on the negative side. If the atom had 2 electrons, its charge would double in a negative direction. By calling a proton, a 1+ charge electrical unit, we are saying its actual electrical measurement is +1.6022x10-19 coulomb, which is 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; about 1,840 times heavier than the electron.
The Neutron: The above calculations, by the 1920's, clarified the picture of the simplest atom – hydrogen (H). It consists of a dense central nucleus that has a 1+ proton. But outside the nucleus, the atom continues as mostly empty space with a balancing 1 electron in orbital. We say “orbital” instead of “orbit” because an electron is thought of not only as a particle but also as a wave so its particle orbit, in wave form, is smeared around the nucleus in an “orbital”. Measurements showed that the radius of the H atom (from its center in nucleus to its outermost electron orbital) is c.20,000 times the radius of its nucleus. If you imagine such a hydrogen atom the size of Houston Astrodome, its nucleus would be the size of a small marble.  As physicists studied the atoms that were the smallest and next smallest, of the elements, hydrogen (H) and helium (He), a physical measurement figuratively threw a monkey wrench into the above described atom. Experiments showed 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 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 show it to be 4 times as heavy. To explain this it was guessed that the He nucleus, in addition to its two protons, contained 2 electrically neutral particles (neutrons) of the same weight as the proton. In 1932, James Chadwick tested this by bombarding the metal element beryllium with α-particles (He2+; 2 protons of the helium nucleus with its surrounding orbital stripped of its 2 single negative-charged electrons). The α-particles, being relatively massive and electrically positive were attracted by the beryllium electro-negative orbitals and then 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 1935. 
Atoms & Molecules are Basic in the Elements & Compounds:  As with Arabic numbers, where single-digit (1, 2, 3, …) is the basic building block, so matter has basic building blocks – the element atoms, the various combinations of which can form all chemical compounds. The property that makes elements is that each element is made up purely of its own atom. All chemical properties that define the element – atomic valence, electrical charge of its ion – are in the atom of the element.  At next level, the compounds are composed, at their most basic structural unit, of molecules. A molecule, in the analogy of scissoring a substance in half, is the smallest scissor product that one could physically recognize – by color, melting point and other physical attributes – as the compound. In terms of 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 atom has a dense, positively charged nucleus containing 1+ charged proton(s) and no-charge, same weight neutron(s) surrounded by a huge space containing very light-weight negatively charged electrons around the nucleus. The electrical charge of the free atom is zero, which means that the positive charge of its proton(s) in the nucleus is exactly balanced by the negative charge of its electron(s).The positive charge of a nucleus comes from its protons. A same-weight body also exists in the nucleus but is electrically neutral, the neutron. Practically, the weight of an atom is accounted for by the sum weight of its neutrons and protons, so if we know that atom H has 1 proton (normal Hydrogen with no neutron) and atom He has 2 protons and 2 neutrons (Helium), 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) 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 its 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) a set distance from center of the atom. According to latest data, electrons are not singular bodies or particles, and so do not revolve 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.We are talking here about an H hydrogen atom. Actual atoms of different elements differ from each other by their number of protons and neutrons and by the number of electrons in orbital(s). But each atom in a particular element is same as all other atoms in that pure element. 
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 number of electrons in a neutral atom is the same as its number of protons; that number is its atomic number (AN), and an atom of the same element has an AN that defines the element. The AN contains useful info 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 and in its neutral atom has 3 electrons in orbitals. 
           Atomic Mass/Atomic Weight/Isotopes      Since a neutron and a proton are, practically, the same mass, and an electron’s mass is insignificant, the mass of an atom may be estimated by counting protons and neutrons of the atom. Thus, hydrogen H, the simplest, smallest atom, has 1 proton and no neutrons and atomic mass unit. (AMU) of 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. It is the standard against which the mass of each atom is measured.
Isotopes: In each pure element all the atoms are the same AN (atomic number). But in the pure 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. But a few hydrogen atoms have additionally 1 neutron, giving 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 in mass because of one or more neutrons, it 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 protons and neutrons in each atom multiplied by its number of atoms. The mass unit number is 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 of all the protons and neutrons in all 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 the sum of atoms in my body by the Earth’s gravity at my present position on the 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 x itself), between the smaller body and its gravity attracting body (Earth in this case), the weight of the smaller object of given mass changes 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. Experiments use mass instead of weight.  To give units of weight, scientists use the metric measurement, gram. (Practically, the determination of mass in an experiment is based on fine balance weighing in gram or its decimal; see later in text) 
Avogadro’s Law and Number: the same number of elementary particles (number of atoms, molecules or ions of a pure compound) of any pure element or chemical compound is contained in a weight in grams equal to the element’s atomic mass unit (AMU) or the compound’s molecular weight. In 1811, Avogadro arrived at this prediction, which suggests a unifying principle for all matter in the Universe, 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. This suggested to Avogadro that all pure substances contain the same number of basic particles (atoms or molecules) 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 weight 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 a weight of a compound or element on a fine 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, Avogadro’s number of unit particles are contained in the same volume (22.4 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 gram weight of a solid or 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.  
Molecular Chemical Formulas/Radicals/Ions/Reactions:  Notation for chemicals is a shortcut that shows the atoms of a compound, their proportions, 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 better idea of its actual structure is given by C2H5OH, which tells it is a union of 1 ethyl radical group (-C2H5) and 1 hydroxyl radical (-OH). For more accuracy, ethanol CH3CH2OH, shows the skeleton structure of the molecule, which is C-C-O-H, with carbon atoms having bonding spots for the 5 free hydrogen atoms. Higher accuracy are formulas that show 3-dimensions.(3-D) 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 or ionic hydroxyl radical –OH, are tightly bonded atoms that act like a single atom and, in chemical formula & reactions, act as a unit; for examples, methyl chloride CH3Cl or ethyl alcohol C2H5OH.  You should visualize brackets about a radical, as (C2H5)OH but, in cases where a radical reacts is single unit the brackets are absent. However in a case where a radical is more than one unit, for example (di)methyl sulfide (CH3)2S the brackets are written and a subscript shows the number of radical 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 –CH3CH2 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.


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 with a double-bond oxygen =O actually sticking out of the page at an angle and an –O-H+, which becomes ionic when dissolved in water. “Ionic” means for example that 1+ and 1–  electrically charges separate in water into a 1– 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, I 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). Proton number in an atom is very stable (i.e., number of protons in atomic nucleus never changes; it 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-positivity of the nucleus varies with size and charge of the nucleus and location distance of electron orbitals. The nucleus in large atoms exerts a more powerful pull on electrons than the nucleus in smaller atoms; the pull is most powerful the closer the orbital is to the nucleus.
Electron orbitals are in shells at varying distances from a nucleus. Outermost orbital electrons, each with a negative charge, are less stable than inner electrons because more weakly attracted to the more inwardly distant positive nucleus; so the outermost 1, 2 or 3 electrons tend to get easily detached in atoms of one set of elements, while another set that lacks 1, 2 or 3 outermost electrons  tends to attract and acquire them. When an atom loses 1 or more electrons from orbital, its electric charge becomes unbalanced in positive direction. For example, the electrically neutral hydrogen atom has 1 proton in nucleus and 1 electron in orbital. It tends to lose that electron and then it acquires a 1+ electrical charge (From H, subtracting a 1-negative charge electron makes H+) 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 as neutral atom normally has 9 protons and 9 electrons but it tends to gain 1 electron in outer orbital and, when it does, it becomes fluorine ion (fluoride) with 1-minus electric charge, written F. (F plus a 1-negative charge electron becomes 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 only 1, 2 and 3 electron(s) in outermost orbital, tend to lose these electron(s) easily, i.e., they are electron-donors. Thus H loses a 1-negative electron and becomes the H+ion, Be loses two 1-negative charge electrons and becomes the Be2+ ion, and B loses three 1-negative charge electrons and becomes the B3+ ion. But atoms of elements that lack 1, 2, or 3 electrons to fill outermost orbital shell tend to pick up electrons easily and become similar number charge negative ions (eg, oxygen lacks 2 electrons so O plus two 1-negative charge electrons becomes O2- ion). These are mostly gas elements like oxygen, nitrogen, fluorine and chlorine.  Note here a principle: atoms always tend toward a complete set of orbital electrons in the atom's outer shell.  This explains the formation of ions. 
The 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 source 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., sodium, Na) mixes with an element whose neutral atoms are electron acceptors (e.g., chlorine, Cl), forming the ionic compound Na+Cl, sodium chloride, which is table salt. Ionic compounds, like NaCl, in absence of water, tend to form crystal solids, and 1 mol, or 58.44 grams of NaCl, contains Avogadro number 6.022 x 1023 molecules of NaCl in lattice 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, the ionic electrical bonds dissolve, liberating separate Na+ and Cl- ions (electrolytes) into solution. Pure distilled water, because it has no ions, will not pass electric current. But water in which 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 when salt is put into the water that forms the conductor of electricity to the bulb. That is why ions are ‘stuff of life’; because the ability to pass electrical current is required for all life.          
               Naming Chemical Compounds:   Organic (associated with life) compounds contain carbon (C), usually in combination with elements such as hydrogen (H), oxygen (O), nitrogen (N), sulfur (S) and phosphorus (P). All other compounds are classified as inorganic (associated with non-life). Among common organic carbon C compounds are the gas carbon monoxide (CO) that comes from car engine and the greenhouse gases, carbon dioxide (CO2)  & CH4 methane, the  last 2 the main cause of global warming; and also chemical compounds containing cyanide (CN-), carbonate (CO32-) and bicarbonate (HCO3-). Organic compounds may be ionic, molecular, acids and bases, hydrates.  Naming Ionic Compounds: Most are binary, i.e., compounds formed from 2 elements in ionic form. For naming binary compounds, first comes the metal cation with unchanged spelling followed by its anion partner with changed ending. Thus NaCl (common table salt) is 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 2 different elemental atoms, such as hydroxide (OH-) and cyanide (CN-). Thus, compounds LiOH and KCN are named lithium hydroxide and potassium cyanide. The “-ate” ending is used for anion groups that have, additional oxygen, e.g. “carbonate” (CO32–) and “bicarbonate” (HCO3); the last formula demonstrates the use of “bi-” prefix when H+ ion reduces charge as CO32– + H+à 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. 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 ion on the anion side. Some examples, illustrate. Sodium chloride: Na+ + Cl- à NaCl  ([1+] + [1-] = 0); Zinc Iodide: Zn2+ + 2I- à ZnI2 ([2+] + [2x1-] = 0); Barium Sulfide: Ba2+ + S2-à BaS ([2+] + [2-]=0), both subscripts divisible, so reduce to smallest ratio, Ba2S2àBaS; and Aluminum oxide: Al3+ + O2 à 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 two-positive (2+) charge took the suffix, “-ous” and the three-positive (3+) charge took the suffix, “-ic”, e.g., Fe2+ is ferrous ion and Fe3+ is ferric, giving “ferrous chloride” FeCl2, and, “ferric chloride” FeCl3. It is a simple system and you should know it because many compound names still adhere to it, but in 2014, 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 split into cations and anions. They exist as inorganic gases and organic carbon, hydrogen and oxygen solid compounds like cholesterol. As inorganic gases, their naming is like 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 (straight line like the carbon core compounds –C–C–C–C–). However the most important organic compounds are cyclic, the C atoms form a geometric polygon ring – usually a hexagon or pentagon. A famous example that is part of proteins is the smelly solvent benzene. View its variously written structure:Note benzene is a 6-carbon hexagon, the C’s bond to each other at its core and the H’s jut out on the outer bonding sites. Note the two writings on your left, where no C or H is shown. When one or more of the H’s detaches from the ring molecule it gives types of radicals with bare bonding sites where the detached H atoms were, and 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 indicates a single site bonding on the C atom. Since each C has 4 possible bonding sites, the –C= alternation leaves spaces for 6 H atoms bonding to the 6C's of the cycle. 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, slangily “unsat fat”. Below you see the same cyclic structure as benzene but without the double bonds,Note the suffixes “-ene” (Benzene)  and “-ane” (Cyclohexane).  To tell a reader a structure has 1 or more double-bonds, (-ene) is used. To show no double bond (-ane) is used. Also note that “Benzene” is a traditional name for what also could be named Cyclohexene (cf. Cyclohexane, e.g., a 6-sided cycle, or hexagon of C atoms with degree of saturation indicated by the ene or ane).  
                    Electron Sharing in Chemical Bonds    The formation of molecules is dependent on the chemical bonds between the atoms that form the molecules. These bonds are shown 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 written 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 
                                                                                               H
                                                                               H C H                                                                                                                    H 
To use the word “bond(ing)” means some sort of attraction between atoms. The attraction is based on electron sharing. For an explanatory example, look at 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 electron in its outermost (and only) shell orbital. The hydrogen atom as a singlet H1 does not exist free in the natural state on Earth because all atoms can be said to have an overwhelming inanimate desire to have a full complement of at least 2 electrons in their incomplete outer electron shells. So under normal energy conditions H atoms form H2 molecules of hydrogen gas. The hydrogen H 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 outermost 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 other’s electron, each H atom completes its electron orbital shell and is very satisfied.  This can be pictured by an H,(or, turned around a H)  with the open 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  Note I use the simplest atom, the H, but the same explanation goes for all other atoms to form atom bonds.  Also double bonds like –C=C–, and even triple bonds –CC. These are seen in the unsaturated fats that are good for your health. In these cases, each line of the double or triple bond represents a shared electron pair. And note that when a shared electron pair is part of a chemical bond, it 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, leaving one or more of the electrons to react to form other bonds.  Thus 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. Also these unsaturated compounds are highly reactive and unstable, easily reacting with electron lacking chemicals.               
                        Chemical Equations use symbols to show what happens during a chemical reaction and the amount of chemical substance 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 left of the arrow are reactants and on right, product. An arrow indicating direction shows that, normally, energy-release favors the reaction to run to the production of water. The reverse reaction would require input of energy, e.g., an electric current run through water would dissociate water molecules to hydrogen and oxygen gas. Other reactions show this form of chemical equation with arrow indicating direction favored by energy input or output. Sometime there are double 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 radical group of elements in each molecule. The large front numbers indicate the proportion of molecules  involved in the reaction. (Exception: "1"is  understood) In the "2H2 + O2  becomes 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 would 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. This brings out balancing of chemical reactions.  A catalyst is a chemical that speeds the rate of reaction without getting used up. “Enzyme” is catalyst of  living tissue. We shall run into “enzyme” in studying good health, illness and long life.   Many vitamins are enzymes and many minerals form core of enzyme structure. (Cobalt forms core of vitamin B12; magnesium forms core of chlorophyll) 6CO2 + 6H2O (chlorophyll enzyme in leaf) ->C6H12O6 + 6O2
In the last equation, just above,, you see the photosynthesis reaction that occurs in leaf exposed to sunlight, whereby 6 moles of atmospheric carbon dioxide gas combine with 6 moles of water in the presence of the green pigment catalyst 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, the oxygen of planets with life; and also we see the protective affect of plants against the Global Warming greenhouse effect, by removing carbon dioxide. 
Aqueous Solution, Concentration, Acid/Base   A solution is a mixture of particles (the solute) dissolved in fluid (the solvent). The solute dissolved in solution may be electrolyte or non-electrolyte. Electrolyte solute in water liberates ions (e.g., NaCl sodium chloride in water liberates Na+ and Cl). 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 and is represented as follows: CH3COOH  CH3COO-(acetate anion in water) + H+ (hydrogen ion in water).  Acetic acid is an acid because it liberates H+ in aqueous (water) solution. It is in a class of anions (negative charged ions) that are organic CHO compounds and include proteins. The organic anions because they are almost completely inside cells and cannot pass out through the cell membrane and because they are used up in metabolism are important in electrical transmission in neural system cells (neurons) and also for holding water inside cells. They are attached to inorganic cations like H+so the using up of the organic anion unbalances the cell in favor of hydrogen ion electro-positivity causing our bodies to become increasingly acid during food metabolism.     
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 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
+H-O2-
     H+
shows 2 electric single-positive (H+) jutting-out points balanced against 1 electric double-negative (O2-) corner right angle point. Such molecule with uneven electric charge distribution is called a polar molecule because it contains separated poles of electro negativity and positivity. 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 the 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 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 Concentration of Solutions: The concentration of chemical substances in body fluids like blood or urine is 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).  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 Avogadro’s number of molecules (or ions for ionic solutions). Mol per liter is used for giving concentrations of substance in blood in most other countries 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 low concentrations.  
 The 3 States of Matter as well as TemperatureEvery pure substance can exist physically as solid, liquid and gas. Water can be solid ice, liquid, and steam gas. It changes from solid to liquid to gas with rise in temperature or lower atmosphere pressure.
The temperature units: Centigrade was based on zero degree (0 C) the point where ice melts to water, and each 1 C measurement graduated in 100 parts to 100 C where water boils to steam. Since Celsius replaced Centigrade, the actual basis of the zero degree point is the so called “triple point” where specially 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 absolute zero temperature, the point where all movement would cease, which is zero Kelvin (0 K), or minus 273.15 C. (Note, when temperature is expressed as Kelvin, no degree superscript used) So in converting Celsius (C) to Kelvin, just add 273.15 K units to the Celsius unit. The Fahrenheit is an older system now used in USA.  Celsius = (Fahrenheit minus 32) x 5/9, and Fahrenheit = 9/5 (Celsius) + 32. And note that 0C = 32 Fahrenheit, and that minus 40 Fahrenheit = minus 40 Celsius. 
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 rises and/or air pressure falls, the substance particles become more energetic or less pressed and can’t be held together so they begin to slide over each other and we have fluidity. As heat keeps being increased (or air pressure lowered), the energy (or freedom from pressure) imparted to particles becomes so great that the substance particles fly out of control and become formless gas. Each element or compound has melting/freezing and boiling/liquefaction point at given air pressure & temp, 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. No matter, 1 mole of a pure substance (compound or element) gas at standard atmosphere temperature and pressure has 22.4 liters volume. 
About Gases & Atmospheric Pressure   Measurement Units: 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 various elemental and chemical compound gas molecules. (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 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 lines on the tube. Mercury fills the tube except for a small space at top, which is a relative vacuum. The atmospheric air transmits its weight to the column of mercury, which rises into the vacuum at top and finds a height that represents in millimeters of Hg 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 atmospheric pressure. The unit 1 mm Hg is 1 torr. (After Evangelista Torricelli) 
Energy, Waves, EMG Radiation & SpectrumRadiant energy from the Sun heats Earth; affects global climate, makes wind, snow and rain and produces food. We harness radiant energy when we focus Sun’s rays to make fire. Radiant energy can produce heat across a near vacuum of miles of space. On Earth, thermal energy needs the medium of matter in continuity to transmit its heat.
Chemical energy is stored within the structure of chemical compounds as bonds, the chemical force that holds atoms in place within molecules. When substances participate in chemical reactions, chemical energy may be released as heat when the bonds are broken or it may be stored in bonds of new compounds formed in the chemical reaction.
Your body uses chemical-bond energy storage in parceling out energy units as though the units are money currency. It does this by making a special high-energy bond chemical, adenosine triphosphate, or ATP, that acts like an energy credit card by releasing its high-energy phosphate-bond and in so doing releasing a set amount of energy in a packet for metabolic work (Adenosine TriPhosphate becomes Adenosine DiPhosphate + 1 released phosphate energy unit for metabolic work inside cells).           
         
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 & 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 above the lavender electric field and green magnetic field at 90-degrees to each other. 
The electric field and the magnetic field each have same wavelength, frequency and amplitude but each one vibrates in a plane at right angle 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 energy imparted from the force was applied to start it moving; its speed is affected by the medium transmitting the wave (air, water, or lack of medium as in a vacuum). The wavelength is the distance between wave peaks. The velocity, or speed at which a wave peak travels – called frequency or f,  is measured in cycles per sec (A cycle is a full wave) and is the unit, hertz. (Hz; 1 Hz = 1 cycle per second, or 60 wave peaks passing in 1 minute) The amplitude is the distance of the wave peak from the central baseline (the height of the wave 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 seen in water waves. Speed of transmission is rather slow, 30 to 50 feet (c.9-15 m.) a minute. If we consider a water wave, we understand it as compression and relaxation on the water molecules; the compression being in the wave peak and relaxation in the wave trough. In waves from a pebble dropped into 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.  All 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. The solid parts of the Earth cannot move much, but the liquid seas are dragged back & forth by the combined forces and the result is the tides & waves. Think about barriers to water waves. Solid steel or rock dam stops them, but a sieve does not. 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 occurs.
Sound waves are alternating compression and relaxation on molecules in air set up by 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 intensity of the sound we hear is from the amplitude of its waves. Frequency & amplitude of sound waves is important for human hearing. Lower than 20 vibes per second (Hertz) and higher than 20,000 is outside our range of hearing. Sound waves >20,000 vibes/second are ultrasound range and used in radar and medical body imaging. Amplitude accounts for 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 go around wall segments. High-pitched sound waves are those with smaller wavelength & higher frequencies, i.e., more energetic and thus harder to block.     
            ELECTROMAGNETIC WAVES (EMG)The figure shows the range of  electromagnetic wave energy.  Focus on Type of Radiation. At 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. Note the spectrum of visible light, which is part of the sun’s EMG wave radiation energy. It has been enlarged as the rainbow color spectrum – from your right, 700 nm wavelength is Red, Orange, Yellow, Green Blue, Indigo and down to the 400 nmViolet, or the famous, ROY G. BIV. On each side of the visible sun rays are, to your left the ultraviolet used in tanning, and to your right the infra-red, which is the hottest heat wave in heating lamp. Continuing up in wavelength, the microwaves of oven, 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 differ by producing electrical and magnetic fields that vibrate at 900 planes to each other.  The most energetic EMG waves have shortest wavelength and highest frequency. 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 Relativity says may be closely approached but can never be surpassed. The speed of light is known and constant; wavelength is the speed of light multiplied by the frequency, and in reverse the frequency is wavelength divided by the speed of light. Note the wide range of wavelengths, and see 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 too vague word when used alone.  The EMG waves are dangerous to life to the extent they have very short wavelengths and 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 rough but useful rule of thumb for dangerous radiation is wavelengths shorter than visible light - to your left of the visible light ROY G BIV 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 microwaves - often worried about in cell phones and cooking are to the right of the visible light spectrum and are safe other than the risk of skin burn if you put your hand in microwave oven.  Chapter 6 Continues in next Section c. To read now, click 2.6c Electron Arrangement in Atoms/Quantum/Laser





































































































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