Different chemical elements have different kinds of atoms; the atoms of any particular element are all identical to each other (except for the posibility of having electrical charge).

Atoms join or 'bond' together to form molecules by sharing their electrons. Chemical bonding is essentially the interaction of electrons from one atom with the electrons of another atom. They might join together with others of the same kind. Oxygen molecules contain two identical oxygen atoms. Water molecules each contain two hydrogen atoms and one oxygen atom. When the atoms are of different elements, the substance formed is called a compound. For example, when two hydrogen atoms join together with an oxygen atom, water is formed - H₂O.

Chemically bonding occurs when two particles can exchange or combine their outer electrons in such a way that is energetically favorable. An energetically favorable state can be seen as analogous to the way a dropped rock has a natural tendency to fall to the floor.

When two atoms are close to each other and their electrons are of the correct type, it is more energetically favorable for them to come together and share electrons (become "bonded") than it is for them to exist as individual, separate atoms.

When the bond occurs, the atoms become a compound. Like the rock falling to the floor, they "fall" together naturally.

Molecules in turn can join up in regular patterns, and these are what we know as crystals. Salt is made of molecules of sodium chloride (sodium, Na, and chlorine, Cl) or NaCl.

Molecules can get very complicated. Some proteins contain thousands of atoms per molecule, largely carbon, oxygen, hydrogen, and nitrogen. One of the most complex is DNA (deoxyrobonucleic acid) which contains genetic information of living things, such as how our bodies grow.

The properties and reactions of chemical elements and compounds (color, melting temperature, hardness, solubility, etc) are due to the electrical charges on atoms and also to how they are arranged.

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The integer that you find in each box of the Periodic Chart is the atomic number. The atomic number is the number of protons in the nucleus of each atom. Another number that you can often find in the box with the symbol of the element is not an integer. It is oversimplifying only a little to say that this number is the number of protons plus the average number of neutrons in that element. The number is called the atomic weight or atomic mass.

There are only a few more than one hundred elements. Of those, only eighty-three are not naturally radioactive, and of those, only fifty or so are common enough to our experience to be useful in this course. These elements, though, are going to stay the same for a long time. You may have memorized the states and capitals of the United States. The elements will outlast any political entity. You have certainly memorized and internalized the English alphabet. The elements will be around long after the letters of any alphabet are gone. It would serve you well to know the elements. If you were to attempt to read anything without knowing your letters, you would be in trouble. Let�s say you still have a hard time telling the difference between a �b� and a �d.� Your fluency in reading would be ruined by having to look up the difference every time you encountered one of those letters. Similarly, you should know your elements well enough so that if you read or hear about one of them, you instantly know what they are. Learn how to spell the names of the elements. Learn the symbols. Some of the symbols have one letter, some have two, but each element symbol has one and only one upper case letter in it.

Aluminum.

A very rare metal before the electrolytic process of producing it was discovered in 1886, Aluminum is a common metal to us. The melting point is 660 �C, so it can be melted on a common household stove unless it contains a lower boiling liquid, such as water. Aluminum�s silvery shine when new changes to a powdery gray in the air that gives it a protective coating against further oxidation. Aluminum is easily attacked by acids and bases. It is a good conductor of electricity, particularly on consideration of its weight. Due to the ease of the electrolytic process of refining it, aluminum is so cheap that small amounts of it are considered disposable. It is used for foil wrapping for foods

Antimony

On the Periodic Chart antimony appears on the line between metals and non-metals. Antimony is more brittle and less conductive of heat and electricity than most metals. Antimony is used in alloys, for instance mixing with lead to harden it. Antimony is also used in flame proofing compounds and in paints and pottery.

Argon.

Argon is one of the inert gasses of Group 8 or 18, the noble gases. It does not combine with other elements. Argon is collected from the air by fractional distillation. It is used in the red colored electric fluorescent tubes popularly called �neon lights.�

Arsenic.

It has been known for centuries that arsenic compounds are poisonous. Arsenic is a semi-metal (on the boundary between metals and non-metals) that is used in hardening metals, poisons as insecticides, and coloring materials in paints.

Astatine.

Astatine is the only halogen (Group 7 or 17) element that is naturally radioactive.

Barium.

A Group 2 element, barium is about as soft as lead. Compounds of barium make excellent absorbers of x-ray radiation, so are used to outline organs in medical radiology. White barium compounds are used in paints.

Beryllium.

The least dense of the Group 2 elements, beryllium is a very hard, tough metal. Ores of beryllium are not very plentiful. Its soluble compounds taste sweet.

Bismuth. The element has been known for a long time, but it was often confused with tin or lead centuries ago. The pure metal has a slightly pink color to it on top of the usual metallic silvery shine. For a metal, bismuth has a low melting point and a low electrical conductivity. It is used in alloys for sprinkler systems and for metal casting.

Boron.

Boron is familiar in its use as borax, a water softener, and in boric acid, a mild antiseptic. It is also used in ceramics. Boron is a non-metal element that is not found free in nature.

Bromine. Bromine is a halogen (Group 7 or 17 element). It is one of the few elements liquid at room temperature. Bromine has a melting point of -7 �C and a boiling point of 59 �C. A reddish-brown very irritating poisonous vapor comes from the liquid. The organic compounds of bromine are very important.

Cadmium.

Cadmium is a soft bluish metal that is used in low-melting alloys, high friction-resistant alloys, and electroplating. Cadmium rods are used in control for atomic fission. Cadmium sulfide makes a yellow pigment.

Calcium.

The word �lime� has been used with calcium compounds for many years. Calcium is a Group 2 element that is very abundant in the earth�s crust in compounds, but never seen in nature as the free metal element. It is an essential element for living things, especially in muscles, leaves, bones, teeth, and shells. Calcium is found in limestone. It is used in Portland cement, mortar, plaster, and antacids. Lime, Ca(OH)2, is used to mark off playing fields and for de-acidifying (�sweetening�) agricultural fields. The element form of calcium, a soft metal, was not known until the early in the nineteenth century by electrolysis.

Carbon.

There are three common forms of elemental carbon; carbon black ('soot' or 'lamp black'), graphite, and diamond. More recently, various sizes of Bucky Balls have been found to be another allotropic form of carbon. Bucky Balls are geodesic dome-shaped balls of carbon atoms in discrete paterns named after Buckminster Fuller, the predictor of such arrangements. Carbon is not known to form ionic bonds, but only covalent bonds, of which it can make four single covalent bonds per atom. The four covalent bond arrangement gives carbon the geometrical capability to make an incredible number of compounds, called organic compounds, with carbon chains as the �backbone� of a large molecule. One might say that the bonding of carbon makes possible the existence of living things as we know them.

Cesium.

Cesium is a Group 1 element used in some photoelectric cells and as a catalyst in organic reactions. Cesium salts are important phosphors (glowing materials) on the front of phosphorescent color television recievers.

Chlorine.

Elemental chlorine is a greenish dense gas that has been used in wartime as a poison gas. It is found in nature as the chloride, mostly of sodium. (Sodium chloride is �table salt.�) Chloride, the negative ion of chlorine dissolved in water, is one of the common electrolytes in living things. Elemental chlorine is released into water for drinking or swimming to control bacterial and fungal growth. Chlorine is used in bleaches and organic compounds. Chlorine is a non-metal element of the halogen group.

Chromium.

The word 'chrome' is connotes 'bright and shiny.' In fact, chromium is used as an electroplated cover on many automobiles. Chromium is a metal element in many ways resembling iron. It is used in alloys, often with iron, to make harder metals and stainless alloys. The compounds of chromium have many brilliant varied colors, and so are used as pigments.

Copper.

Evidence of copper mining and smelting goes back over five thousand years into human prehistory. The metal element is a characteristic golden-red. It is one of the best conductors of heat and electricity. The best copper for use in electric wires is the very pure copper that comes from using electrolysis as a final purification step. Copper was used in swords before brass and bronze, both alloys of copper that are harder and hold an edge better. Copper is about the easiest metal to smelt. Some distinctive blue-green rocks heated to a reasonable temperature are all the primitive metallurgist needs to get copper. The most important use we have for copper at this time is the conduction of electricity.

Deuterium

. Deuterium is not an element, but one of only two named isotopes, both isotopes of hydrogen. Deuterium is called �heavy hydrogen� because it has a neutron in the nucleus along with a single proton.

Fluorine.

Pronounce 'flue ring' without the 'g' and it might be easier to remember the unusual spelling of fluorine. Fluorine is the least dense, the smallest element number, of the halogen group, Group 7 or 17. Element fluorine is a pale greenish-yellow gas that is extremely poisonous and extremely active chemically. Fluorine is used in hydrofluoric acid to etch glass. Sodium fluoride (say, 'flew ride') in very small quantities is used in drinking water to prevent dental decay. Many organic compounds containing fluorine are common useful materials such as Freon and Teflon.

Francium.

The largest (highest element number) Group 1 (alkali metal) element, francium is radioactive. It is the most active of the alkali metals. It is a natural decay product of actinium.

Germanium.

In making the primitive Periodic Chart, Mendeleev knew to skip a place for an element not yet found. By extrapolation from the chart, Mendeleev predicted the properties of Germanium. The melting point of 32 �C permits Germanium to be melted in a person�s hand. Germanium is used the manufacture of semiconductors.

Gold.

Gold is likely the earliest metal known to humanity because it can be found in its native form and is easier to work (softer) than copper, which also is found in its native form. Gold is the least active of the metals. The gold of the ancient Incas buried many hundreds of years can be unearthed as shiny as it was when new. Gold is an excellent conductor of heat and electricity. It is used in electrical circuitry that is either exposed to weathering or must be reliable for many years. Gold is the most malleable material. It can be pounded into incredibly thin sheets. Pure gold is too soft a metal to make swords, but it is commonly used for jewelry. In the U.S. Most gold jewelry is 14 carat or about 58% gold in the alloy. The distinctive metallic yellow of gold is known and highly valued throughout the world.

Helium.

The name helium refers to the sun because it was first detected in spectroscopic lines from sunlight. Helium is the lightest of the noble gasses, Group 18. Helium is difficult to acquire by fractional distillation of air because of its low boiling point, but it is available directly from the ground in helium wells in Texas, USA. It is used to inflate lighter-than-air balloons and airships and for artificial atmosphere for deep diving.

Hydrogen.

The most famous mental picture of hydrogen is the burning of the zeppelin Hindenburg. There are some who claim that the fire that finished the Hindenburg was lit by the fabric that contained it rather than the explosive tendencies of the hydrogen itself, but a lot of hydrogen burned that day.

Hydrogen is the lightest (least dense) of the elements and the lightest of the gasses. The lift that the Hindenburg got from the elemental hydrogen in its gas bags was the best in the world -- with the one small flaw that hydrogen burns explosively with oxygen to make water. Airships today use another �lighter-than-air� gas, helium, to get lift.

Almost all the hydrogen on earth is in the form of compounds, mostly water. Elemental hydrogen is one of the major components of stars. Large amounts of elemental hydrogen are used for fixing nitrogen for fertilizers and for hydrogenation of fats and oils. Hydrogen is a diatomic gas as an element. It usually appears at the top of Group 1 on the periodic chart, but hydrogen is not a member of Group 1. With only one proton, hydrogen has only one electron in a shell that can only contain two electrons. Hydrogen can lose one electron to become a positive ion, as in acid, or it can collect another electron to produce a hydride (H-) ion with a full shell. In spite of a marked decrease in research funds, fusion power from hydrogen isotopes deuterium and/or tritium seems almost within the grasp of human technology at this writing (1999).

There are many people working on the possibility of using hydrogen as a fuel. The 'hydrogen economy' would require some changes in the way we do things, but may be the only way we have as our petroleum resources run out. Here are some references on the use of hydrogen as a fuel.

Iodine.

The element looks like a dark gray brittle solid at room temperature, but it easily sublimes into a beautiful purple choking gas. It dissolves in water only slightly, but in alcohol fairly easily to make a purple solution. Iodine in alcohol solution is a commonly used antiseptic. Lack of iodine in human beings causes an enlargement of the thyroid gland called goiter. We don�t see much goiter in our culture because iodized table salt has a small amount of iodine added to it. Iodine is a halogen. As a gas it is a diatomic molecule.

Iron.

Iron is the metal on which our civilization is built. It is usually not used as the pure element, but as the major component of a large number of alloys called steel. Carbon is one of the elements added to iron to make various alloys. In general, the more carbon in the mixture, the more brittle the iron alloy is. Pig iron, the material direct from the blast furnace, can be cast into shapes. The carbon content of pig iron can be about three percent. Other metals can be added to the iron to make alloys with much improved properties, such as stainless steel. Iron is magnetic and a decent conductor of electricity in its pure form.

Krypton.

Krypton is an inert gas. As the other noble gases, it produces a bright line spectrum in fluorescent tubes. Krypton�s light output is a brilliant yellow-green. If you were a writer of fiction and wanted to describe a mineral with unlikely properties, you might claim that the mineral would be a compound of Krypton, since there are none.

Lead.

With a melting temperature of 327 �C and a commonly available ore, lead is an easy metal to acquire and shape. Lead is malleable and fairly soft. Lead salts are poisonous. There is some suspicion that lead contributed to the downfall of the Roman Empire due to the use in water pipes and cups for warming mulled wine. There is some argument that the Roman upper classes having lead pipes and drinking mulled wine poisoned themselves. Lead is used in automotive electric batteries, solder for electronic devices, and pigments. Lead was commonly used in making the pigments for house paint until the ninteen fifties. Many older houses now must bear the warning that very young children should not live in such places until the old paint is removed for fear of lead poisoning.

Lithium.

As all the Group 1 elements, the alkali metals, Lithium reacts with water, so it is not found in nature. As a metal element it is as soft as cool butter. It burns in air to form the oxide. Industrially it is used in alloys to increase the tensile strength of the mixture. It emits a beautiful crimson flame test. Medically it is used in compounds to clear out uric acid and to relieve depression.

Magnesium. Magnesium is very common in the earth's crust, but only in compounds. The metal is a light, strong, metal element that will burn in air with a bright blue-white flame. It is used in places where tough metal alloys are needed to be light weight, such as automobile wheels (mag wheels) and airplane and helicopter bodies.

Manganese.

A magnetic metal with many of the properties of iron, manganese is more brittle than iron. It is used mainly in steel alloys to harden them. Potassium permanganate is one of the best-know of the compounds of manganese. Potassium permanganate is a beautiful purple compound that is an excellent oxidizing agent.

Mercury.

The metal element is a liquid between -39 �C and 356 �C. It has a regular coefficient of expansion, so the most likely place for you to have seen elemental mercury is in a liquid thermometer. As a liquid conductor of electricity, mercury is used as the switch in thermostats. Mercury makes alloys called amalgams with many metals. For many years amalgams have been used as fillings for teeth. The name quicksilver, an old English name, means, alive metal, or lively metal due to the way the metal coheres to itself but does not wet many surfaces commonly wet by water. Liquid mercury has a fairly high vapor pressure, and the gas from it is a cumulative poison.

Neon.

The gas that lends its name to the group of fluorescent lights made from inert gases itself only produces a red-orange color in the gas tubes. It is prepared by fractional distillation of liquid air. As an inert element, it does not combine with other elements to make compounds.

Nickel.

Yes, there is some nickel in the USA five cent coin. Nickel is used for many alloys, generally making the alloy stronger and less chemically active. It is a metal element in the iron and cobalt group. Nickel with large surface area is used as a catalyst for the hydrogenation of edible oils. Nickel is used in some storage batteries.

Nitrogen.

There is a lot of nitrogen in front of your face! About eighty percent of the atmosphere is elemental nitrogen. Nitrogen gas is a diatomic molecule with a triple (covalent) bond between the atoms. The strong bond makes the element somewhat inert. It is difficult to get atmospheric nitrogen into compound. Since many organic compounds require nitrogen, its availability is a limiting factor on biological growth. Thus, nitrogen compounds are included in many fertilizers. (See Phosphorus about fertilizers.) The process of combining nitrogen into compounds is called fixing. Ammonia is produced by the Haber process as one of the steps in producing nitrogen compounds. Nitrogen compounds may be somewhat unstable, therefore usable in explosives.

There is a wonderful article in the July 1997 issue of the SCIENTIFIC AMERICAN beginning on page 76, "Global Population and the Nitrogen Cycle," by Vaclav Smil. This is a part of the intriguing story of how chemistry and history and farming and ecology are all intertwined with the nitrogen cycle.

Oxygen.

Just as nitrogen, oxygen is abundantly available in element form in the atmosphere. Oxygen as a diatomic molecule with double bonds between the atoms is about twenty percent of the air. Pure oxygen at atmospheric pressures can fully ignite a glowing wood splint, this being the classic test for the presence of oxygen. Every element except for the inert gases can chemically combine with oxygen, the metals in ionic bonds and the non- metals with covalent bonds. Oxygen is necessary for the respiration of all animals and almost all combustion.

Phosphorus.

Along with nitrogen and potassium, phosphorus is also a limiting factor in the growth of living things. The standard notation for fertilizer is N P K. N is the percentage of nitrogen as nitrate. P is the percentage of phosphorus as phosphate, and K is the percentage of potassium. Phosphates in waste water pumped directly into streams will produce a proliferation of algae that clog waterways. Elemental phosphorus comes in three allotropes, the white or yellow phosphorus being the most common. White phosphorus can be changed to the red form by heating to 250 �C, just thirty degrees below the boiling point, and cooling. Red phosphorus does not spontaneously ignite in air and is not poisonous as is the white or yellow phosphorus.

Platinum.

The free element platinum is a metal almost as inactive as gold. For this reason and its silvery beauty, platinum has been considered a precious metal. Most platinum is mined as a small by-product of nickel mining. Finely divided platinum can serve as a catalyst for several reactions.

Potassium.

The word potash refers to potassium. That name may have come from the practice of leaching potassium (and sodium) hydroxide from the ashes of burnt wood. The lye (hydroxides) would be boiled with fat (from meats cooked on that same fire) to make soap. Potassium metal is a very soft metal that very quickly becomes tarnished in the air. The tarnishing can be slowed by storing the metal under kerosene. Potassium is a Group 1 element, an alkali metal. It reacts violently in water, burning with a bright blue-white flame. Potassium ions are not only not poisonous, but they are required by living things. (See Phosphorus about fertilizers.) Potassium chloride is often used as a table salt substitute for people who wish to limit the sodium intake.

Radium.

Radium is the element that first made Madam Curie famous. She and a coworker were the first to isolate the element. Pierre and Marie Curie were both scientists working in turn-of-the-century Paris. Having an active social life, the Curies would throw parties at their home and show guests a test tube of the new material. The test tube would glow brightly, and the glow was visible even through closed eyelids! The Curies didn't know that the rays from the radium were harmful. Marie Curie suffered from what we now would call radiation sickness. Her beautifully luminescent radium was the first element found to be radioactive. The strange fact of radium giving off light and spontaneously changing to another element forever altered our ideas of the structure of the atom. Radium is a Group 2 element, but because of its radioactivity, it is not usually found in basic chemistry labs.

Radon.

The heaviest of the inert gases, radon is a radioactive gas. Unlike its lighter cousins, radon is not used in fluorescent lights. The radiation from radon has been shown to cause cancer in human beings in some buildings in which the radon seeps in from cracks in basement floors. Be careful to not confuse radon with radium, a radioactive metal element.

Rubidium.

The name of rubidium comes from the deep red flame test it gives. As it is an alkali metal, Group 1, it makes similar compounds to sodium and potassium. A very soft metal element, it reacts violently with water.

Silicon.

Pronounce the name to rhyme with 'kill-a-don' to keep from confusing it with a class of its compounds, silicones, pronounced to rhyme with 'kill-a-phone'. Elemental silicon in its most common allotropic form looks like a lump of very shiny coal. It is not malleable. Hit a lump of silicon and it shatters, spraying needle-sharp shards. It is a semi-conductor of electricity, a property that makes it valuable in electronic components. Silicon is the second most abundant element in the earth's crust, but it is never found in the native state. Chemically silicon is similar to carbon. It does not make ionic bonds, but makes four covalent bonds. Sand and other minerals are made of silicon dioxide. Silicones, organic compounds with silicon in placed of carbon, have been used to for an incredible number of biological tasks.

Silver.

Known far before the Romans called it argentum, silver can be found in the native state and in compounds. Silver is the best of conductors of heat and electricity and almost the most malleable and ductile metal, second only to gold. Silver is harder than gold, but it reacts with some acids. The black tarnish on silver is silver sulfide, usually from combination with sulfur compounds in the air. Dilute silver nitrate is used as an antiseptic. Silver chlorides change on exposure to light, this reaction being the basis for black-and-white photography.

Sodium.

Sodium is the most abundant of the alkali metals (Group 1) in the earth's crusts, but it is never found in the native state. Sodium chloride, table salt, is its most common compound. Sodium produces a pair of very strong lines close together in the yellow color region as an emission spectrum, giving the sodium flame test the characteristic yellow color. Free elemental sodium is a very soft metal that reacts quickly with the air. As with other alkali metals, storing it under kerosene decreases its availability to the moisture in the air. Almost all the salts of sodium are soluble in water. Baking soda is sodium bicarbonate. Soda lye, or caustic soda, is sodium hydroxide. Sodium ions are needed by most living things.

CONTINUED - PART 2

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