Element, Chemical

Element, Chemical

A survey of the elements

History of the elements

Organization of the elements

Orphan elements

Resources

A chemical element is a fundamental substance of the material world, one that cannot be divided into a more elementary substance by chemical processes. Each element has an identity; for example, gold consists of only gold atoms, and a gold atom is unlike any other atom. Indeed, a gold atom can be split, but the subatomic particles (electrons, protons, and neutrons) that constitute a gold atom are not gold. It could be said that subatomic particles are generic, interchangeable. Atoms, on the other hand, have an identity, and constitute the identity of an element.

A chemical element is a substance made up of only one kind of atom (atoms having the same atomic number). A compound, on the other hand, is made up of two or more kinds of atom combined together in specific proportions.

The atomic number of an element is the number of protons found in the nucleus of each atom of that element; the number of protons in the nucleus equals the number of electrons that can bind to the atom. (Since electrons and protons have equal but opposite electrical charges, atoms can bind as many electrons to themselves as they have protons in their nuclei.) Because the chemical properties of an atom—the ways in which it binds to other atoms—are determined by the number of electrons that can bind to its nucleus, every element has a unique set of chemical properties.

Some elements, such as the rare gases, exist as collections of single atoms; such a substance is monatomic.

Two dozen of the most common and/or important chemical elements
		Percent of all atoms (a)
Element	Symbol	In the universe	In the Earth’s crust	In sea water	In the human body	Characteristics under ordinary room conditions
(a) If no number is entered, the element constitutes less than 0.1 percent.
Aluminum	Al	—	6.3	—	—	A lightweight, silvery metal
Calcium	Ca	—	2.1	—	0.2	Common in minerals, seashells, and bones
Carbon	C	—	—	—	10.7	Basic in all living things
Chlorine	Cl	—	—	0.3	—	A toxic gas
Copper	Cu	—	—	—	—	The only red metal
Gold	Au	—	—	—	—	The only yellow metal
Helium	He	7.1	—	—	—	A very light gas
Hydrogen	H	92.8	2.9	66.2	60.6	The lightest of all elements; a gas
Iodine	I	—	—	—	—	A nonmetal; used as antiseptic
Iron	Fe	—	2.1	—	—	A magnetic metal; used in steel
Lead	Pb	—	—	—	—	A soft, heavy metal
Magnesium	Mg	—	2.0	—	—	A very light metal
Mercury	Hg	—	—	—	—	A liquid metal; one of the two liquid elements
Nickel	Ni	—	—	—	—	A noncorroding metal; used in coins
Nitrogen	N	—	—	—	2.4	A gas; the major component of air
Oxygen	O	—	60.1	33.1	25.7	A gas; the second major component of air
hosphorus	P	—	—	—	0.1	A nonmetal; essential to plants
otassium	K	—	1.1	—	—	A metal; essential to plants; commonly called “potash”
Silicon	Si	—	20.8	—	—	A semiconductor; used in electronics
Silver	Ag	—	—	—	—	A very shiny, valuable metal
Sodium	Na	—	2.2	0.3	—	A soft metal; reacts readily with water, air
Sulfur	S	—	—	—	0.1	A yellow nonmetal; flammable
Titanium	Ti	—	0.3	—	—	A light, strong, noncorroding metal used in space vehicles
Uranium	U	—	—	—	—	A very heavy metal; fuel for nuclear power

Others may exist as molecules that consist of two or more atoms of that element bonded together. For example, oxygen (O) can remain stable as either a diatomic (two-atom) molecule (O₂ ) or a triatomic (three-atom) molecule (O₃ ). (O₂ is the form of oxygen that humans breathe; O₃ [ozone] is toxic to animals and plants, yet ozone in the upper atmosphere screens Earth from harmful solar radiation.) Phosphorus (P) is stable as a four-atom molecule (P₄ ), while sulfur (S) is stable as an eight-atom molecule (S₈ ).

Even though all atoms of a given element have the same number of protons in their nuclei, they may not have the same number of neutrons in their nuclei. Atoms of the same element having different numbers of neutrons in their nuclei are termed isotopes of that element. An isotope is named according to the sum of the number of protons and the number of neutrons in its nucleus. For example, 99% of all carbon (C), atomic number 6, has 6 neutrons in the nucleus of each atom; this isotope of carbon is called carbon 12 (¹²C). An isotope is termed stable if its nuclei are permanent, and unstable (or radioactive) if its nuclei occasionally explode. Some elements have only one stable (non-radioactive) isotope, while others have two or more. Two stable isotopes of carbon are¹²C (6 protons, 6 neutrons) and¹³C (6 protons, 7 neutrons); a radioactive isotope of carbon is¹⁴ (6 protons, 8 neutrons). Tin (Sn) has ten stable isotopes. Some elements have no stable isotopes; all their isotopes are radioactive. All isotopes of a given element have the same outer electron structure and therefore the same chemical properties.

Ninety-two different chemical elements occur naturally on Earth; 81 of these have at least one stable isotope. Other elements have been made synthetically

Table 2. A Who’s Who of the Elements. (Thomson Gale.)
A who’s who of the elements
Element	Distinction	Comment
Astatine (At)	The rarest	Rarest of the naturally occurring elements
Boron (B)	The strongest	Highest stretch resistance
Californium (Cf)	The most expensive	Sold at one time for about $1 billion a gram
Carbon (C)	The hardest	As diamond, one of its three solid forms
Germanium (Ge)	The purest	Has been purified to 99.99999999 percent purity
Helium (He)	The lowest melting point	–457.09°F (–271.72°C) at a pressure of 26 times atmospheric pressure
Hydrogen (H)	The lowest density	Density 0.0000899 g/cc at atmospheric pressure and 32°F (0°C)
Lithium (Li)	The lowest-density metal	Density 0.534g/cc
Osmium (Os)	The highest density	Density 22.57 g/cc
Radon (Rn)	The highest-density gas	Density 0.00973 g/cc at atmospheric pressure and 32°F (0°C)
Tungsten (W)	The highest melting point	6, 188°F (3, 420°C)

(artificially), usually by causing the nuclei of two atoms to collide and merge. Since 1937, when technetium (Tc, atomic number 43), the first synthetic element, was made, the number of known elements has grown as nuclear chemists made new elements. Most of these synthetic elements have atomic numbers higher than 92 (i.e., more than 92 protons in their nuclei); since 92 is the atomic number of uranium (U), these artificial heavy elements are called transuranium (past-uranium) elements. The heaviest element discovered and verified so far is Element 111, Roentgenium (Rg), which was discovered in 1994. Since then, Elements 112 (Ununbium [Uub], discovered in 1996), 113 (Ununtrium [Uut], 2003), 114 (Ununquadium [Uuq], 1998), 115 (Ununpentium [Uup], 2003), and 116 (Ununhexium [Uuh], 2000) have been discovered but not verified by independent scientific studies.

A survey of the elements

Of the 116 currently known elements, 11 are gases, two are liquids, and 103 are solids. (The transuranium elements are presumed to be solids, but since only a few atoms at a time can be synthesized it is impossible to be sure.) Many elements, such as iron (Fe), copper (Cu), and aluminum (Al), are familiar everyday substances, but many are unfamiliar, either because they are not abundant on Earth or because they are not used much by human beings. Less-common naturally occurring elements include dysprosium (Dy), thulium (Tm) and protactinium (Pa).

Every element (except a few of the transuranium elements) has been assigned a name and a one- or two-letter symbol for convenience in writing formulas and chemical equations; these symbols are shown above in parentheses. For example, to distinguish the four elements that begin with the letter c, calcium is symbolized as Ca, cadmium as Cd, californium as Cf, and carbon as C.

Many of the symbols for chemical elements do not seem to make sense in terms of their English names— Fe for iron, for example. Those are mostly elements that have been known for thousands of years and that already had Latin names before chemists began handing out the symbols. Iron is Fe for its Latin name, ferrum. Gold is Au for aurum, sodium is Na for natrium, copper is Cu for cuprum, and mercury is Hg for hydrargyrum, meaning liquid silver, which is exactly what it looks like, but is not.

Notice that only two elements taken together— hydrogen and helium—make up 99.9% of the atoms in the entire universe. That is because virtually all the mass in the universe is in the form of stars, and stars are made mostly of H and He. Only H and He were produced in the big bang that (theoretically) began the universe; all other elements have been built up by nuclear reactions since that time, either naturally (in the cores of stars) or artificially (in laboratories). On Earth, only three elements—oxygen, silicon and aluminum—make up more than 87% of the Earth’s crust (the rigid, rocky outer layer of the planet, about 10.5 mi [17 km] under most dry land [less under the oceans]). Only six more elements—hydrogen, sodium, calcium, iron, magnesium, and potassium—account for more than 99% of Earth’s crust.

The abundance of an element can be quite different from its importance to humans. Nutritionists believe that some 24 elements are essential to life, even though many are fairly rare and are needed in only tiny amounts.

History of the elements

Many substances now known as elements have been known since ancient times. Gold (Au) was found and made into ornaments during the late Stone Age, some 10, 000 years ago. More than 5, 000 years ago, in Egypt, the metals iron (Fe), copper (Cu), silver (Ag), tin (Sn), and lead (Pb) were also used for various purposes. Arsenic (As) was discovered around 1250 AD, and phosphorus (P) was discovered around 1674. By 1700, about 12 elements were known, but they were not yet recognized as they are today.

The concept of elements—i.e., the theory that there are a limited number of fundamental pure substances out of which all other substances are made—goes back to the ancient Greeks. Empedocles (c. 495–435 BC) proposed that there are four basic roots of all materials: earth, air, fire and water. Plato (c. 427–347 BC) referred to these four roots as stoicheia elements. Aristotle (384–322 BC), a student of Plato’s, proposed that an element is “one of those simple bodies into which other bodies can be decomposed and which itself is not capable of being divided into others.” Except for nuclear fission and other nuclear reactions discovered more than 2, 000 years later, by which the atoms of an element can be decomposed into smaller parts, this definition remains accurate.

Several other theories were generated throughout the years, most of which have been dispelled. For example, Swiss physician and alchemist Theophrastus Bombastus von Hohenheim (c. 1493–1541), also known as Paracelsus, proposed that everything was made of three principles: salt, mercury, and sulfur. An alchemist named van Helmont (c. 1577–c.1644) tried to explain everything in terms of just two elements: air and water.

Eventually, English chemist Robert Boyle (1627– 1691) revived Aristotle’s definition and refined it. In 1789, French chemist Antoine Lavoisier (1743–1794) was able to publish a list of chemical elements that met Boyle’s definition. Even though some of Lavoisier’s elements later turned out to be compounds (combinations of actual elements), his list set the stage for the adoption of standard names and symbols for the various elements.

Swedish chemist J. J. Berzelius (1779–1848) was the first person to employ the modern method of classification: a one- or two-letter symbol for each element. These symbols could be put easily together to show how the elements combine into compounds.

For example, writing two Hs and one O together as H₂O would mean that the particles (molecules) of water consist of two hydrogen atoms and one oxygen atom, bonded together. Berzelius published a table of 24 elements, including their atomic weights, most of which are close to the values used today.

By the year 1800 only about 25 true elements were known, but progress was relatively rapid throughout the nineteenth century. By the time Russian scientist Dmitri Ivanovich Mendeleev (1834–1907) organized his periodic table in 1869, he had about 60 elements to reckon with. By 1900, there were more than 80. The list quickly expanded to 92, ending at uranium (atomic number 92). There it stayed until 1940, when synthesis of the transuranium elements began.

Organization of the elements

The task of organizing more than a hundred very different elements into some simple, sensible arrangement would seem difficult. Mendeleev’s periodic table, however, is the answer. It even accommodates the synthetic transuranium elements without strain. In this encyclopedia, each individual chemical element is discussed under at least one of the following types of entry: (1) Fourteen particularly important elements are discussed in their own entries. They are aluminum, calcium, carbon, chlorine, copper, hydrogen, iron, lead, nitrogen, oxygen, silicon, sodium, sulfur, and uranium. (2) Elements that belong to any of seven families of elements—groups of elements that have similar chemical properties—are discussed under their family-name headings. These seven families are the actinides, alkali metals, alkaline earth metals, halogens, lanthanides, rare gases, and transuranium elements. (3) Elements that are not discussed either under their own name or as part of a family (orphan elements) are discussed briefly below. Any element that is not discussed below can be found in the headings described above.

Orphan elements

Actinium. The metallic chemical element of atomic number 89, with symbol Ac, specific gravity 10.07, melting point 1, 924°F (1, 051°C), and boiling point 5, 788°F (3, 198°C). All isotopes of this element are radioactive; the half-life of its most stable isotope, actinium-227, is 21.8 years. Its name is from the Greek aktinos, meaning ray.

Antimony. The metallic chemical element of atomic number 51, with symbol Sb, atomic weight 121.8, specific gravity 6.69, melting point 1, 167°F(630.63°C), and boiling point 2, 889°F (1, 587°C). One of its main uses is to alloy with lead in automobile batteries; actinium makes the lead harder.

Arsenic. The metallic chemical element of atomic number 33, with symbol As, atomic weight 74.92, specific gravity 5.73 in gray metallic form, and melting point 1, 503°F (817°C). It sublimes (solid turns to gas) at 1, 137°F (614°C). Arsenic compounds are poisonous.

Bismuth. The metallic chemical element of atomic number 83, with symbol Bi, atomic weight 208.98, specific gravity 9.75, melting point 520.5°F (271.4°C), and boiling point 2, 847.2°F (1, 564°C). Bismuth oxychloride is used in pearlized cosmetics. Bismuth subsalicylate, an insoluble compound, is the major ingredient in Pepto-Bismol^®. The soluble compounds of bismuth, however, are poisonous.

Boron. The non-metallic chemical element of atomic number 5, with symbol B, atomic weight 10.81, specific gravity (amorphous form) 2.37, melting point 3, 767°F(2, 075°C), and boiling point 7, 232°F(4, 000°C). Common compounds are borax, Na₂B₄O₇ •10H₂O, used as a cleansing agent and water softener, and boric acid, H₃BO₃, a mild antiseptic and an effective cockroach poison.

Cadmium. The metallic chemical element of atomic number 48, with symbol Cd, atomic weight 112.4, specific gravity 8.65, melting point 609.92°F (321.07°C), and boiling point 1, 413°F (767°C). A soft, highly toxic metal used in silver solder, in many other alloys, and in nickel-cadmium rechargeable batteries. Because it is an effect absorber of moving neutrons, it is used in control rods for nuclear reactors to slow the chain reaction.

Chromium. The metallic chemical element of atomic number 24, with symbol Cr, atomic weight 51.99, specific gravity 7.19, melting point 3, 465°F (1, 907°C), boiling point 4, 840°F (2, 671°C). It is a hard, shiny metal that takes a high polish. It is used to electroplate steel for protection against corrosion and as the major ingredient (next to iron) in stainless steel. Alloyed with nickel, it makes Nichrome^®, a high-electrical-resistance metal that gets red hot when electric current passes through it; toaster and heater coils are made of Nichrome^® wire. Chromium is named from the Greek chroma, meaning color, because most of its compounds are highly colored. Chromium is responsible for the green color of emeralds.

Cobalt. The metallic chemical element of atomic number 27, with symbol Co and atomic weight 58.93. Cobalt is a grayish, hard, brittle metal closely resembling iron and nickel. These three metals are the only naturally occurring magnetic elements on Earth.

Gallium. The metallic chemical element of atomic number 31, with symbol Ga, atomic weight 69.72, melting point 85.6°F (29.78°C), and boiling point 3, 999°F (2, 204°C). Gallium is frequently used in the electronics industry and in thermometers that measure a wide range of temperatures.

Germanium. The metallic chemical element of atomic number 32, with symbol Ge and atomic weight 72.59. In pure form, germanium is a brittle crystal. It was used to make the world’s first transistor and is still used as a semiconductor in electronics devices.

Gold. The metallic chemical element of atomic number 79, with symbol Au and atomic weight 196.966. This most malleable of metals was probably one of the first elements known to humans. It is usually alloyed with harder metals for use in jewelry, coins, or decorative pieces.

Hafnium. The metallic chemical element of atomic number 72, with symbol Hf, atomic weight 178.49, melting point 4, 040.6 ±68°F (2, 227 ±20°C), and boiling point 8, 315.6°F (4, 602°C). Hafnium is strong and resistant to corrosion. It also absorbs neutrons well, making it useful in control rods of nuclear reactors.

Indium. The metallic chemical element of atomic number 49, with symbol In, atomic weight 114.82, melting point 313.89°F (156.61°C), and boiling point 3, 776°F (2, 080°C). Indium is a lustrous, silvery metal that bends easily. It is often alloyed with other metals in solid-state-electronics devices.

Iridium. The metallic chemical element of atomic number 77, with symbol Ir and atomic weight 192.22. Iridium is an extremely dense metal that resists corrosion better than most others. In its pure state, it is often used in aircraft spark plugs.

Manganese. The metallic chemical element of atomic number 25, with symbol Mn and atomic weight 54.93. The biggest use of manganese is in steelmaking, where it is alloyed with iron. This element is required by all plants and animals, so it is sometimes added as manganese oxide to animal feed.

Mercury. The metallic chemical element of atomic number 80, with symbol Hg, atomic weight 200.59, melting point -37.96°F (-38.87°C), and boiling point 673.84°F (356.58°C). Mercury is highly poisonous and causes irreversible damage to the nervous and excretory systems. This element was long used in thermometers because it expands and contracts at a nearly constant rate; however, mercury thermometers are being phased out in favor of alcohol-based and electronic thermometers because of mercury’s high toxicity.

Molybdenum. The metallic chemical element of atomic number 42, with symbol Mo, atomic weight 95.94, melting point 4, 753°F (2, 623°C), and boiling point 8, 382°F (4, 639°C). Molybdenum is used to make superalloyed metals designed for high-temperature processes. It is also found as a trace element in plant and animal tissues.

Nickel. The metallic chemical element of atomic number 28, with symbol Ni and atomic weight 58.71. Nickel is often mixed with other metals, such as copper and iron, to increase the alloy’s resistance to heat and moisture.

Niobium. The metallic chemical element of atomic number 41, with symbol Nb, atomic weight 92.90, melting point 4, 474.4 ±50°F (2, 468 ±10°C), and boiling point 8, 571.2°F (4, 744°C). Niobium is used to strengthen alloys used to make lightweight aircraft frames.

Osmium. The metallic chemical element of atomic number 76, with symbol Os and atomic weight 190.2. Osmium is hard and dense, weighing twice as much as lead. The metal is used to make fountain pen tips and electrical devices.

Palladium. The metallic chemical element of atomic number 46, with symbol Pd and atomic weight 106.42. Palladium is soft. It also readily absorbs hydrogen and is, therefore, used to purify hydrogen gas.

Phosphorus. The nonmetallic chemical element of atomic number 15, with symbol P and atomic weight 30.97. Phosphorus is required by all plant and animal cells. Most of the phosphorus in human beings is in the bones and teeth. Phosphorus is heavily used in agricultural fertilizers.

Platinum. The metallic chemical element of atomic number 78, with symbol Pt, atomic weight 195.08, melting point 3, 215.1°F (1, 768.4°C), and boiling point 6, 920.6 ±212°F (3, 827 ±100°C). Platinum withstands high temperatures well and is used in rocket and jet-engine parts. It is also used as a catalyst in chemical reactions.

Polonium. The metallic chemical element of atomic number 84, with symbol Po and atomic weight 209. Polonium is a product of uranium decay and is 100 times as radioactive as uranium.

Rhenium. The metallic chemical element of atomic number 75, with symbol Re, atomic weight 186.207, specific gravity 21.0, melting point 5, 766.8°F(3, 186°C), and boiling point 10, 104.8°F (5, 596°C). Rhenium is used in chemical and medical instruments, as a catalyst for the chemical and petroleum industries, and in photoflash lamps.

Rhodium. The metallic chemical element of atomic number 45, with symbol Rh and atomic weight 102.91. This element is similar to palladium. Electroplated rhodium, which is hard and highly reflective, is used as a reflective material for optical instruments.

Ruthenium. The metallic chemical element of atomic number 44, with symbol Ru, atomic weight 101.07, specific gravity 12.5, melting point 4, 233.2°F (2, 334°C), and boiling point 7, 502°F (4, 150°C). This element is alloyed with platinum and palladium to form hard, resistant contacts for electrical equipment that must withstand a great deal of wear.

Scandium. The metallic chemical element of atomic number 21, with symbol Sc, atomic weight 44.96, melting point 2, 805.8°F (1, 541°C), and boiling point 5, 127.8°F (2, 831°C). Scandium is a silvery-white metal that develops a yellowish or pinkish cast when exposed to air. It has relatively few commercial applications.

Selenium. The nonmetallic chemical element of atomic number 34, with symbol Se and atomic weight 78.96. Selenium is able to convert light directly into electricity, and its resistance to electrical current decreases when it is exposed to light. Both properties make this element useful in photocells, exposure meters, and solar cells.

Silver. The metallic chemical element of atomic number 47, with symbol Ag and atomic weight 107.87. Silver has long been used in the manufacture of coins. It is also an excellent conductor of heat and electricity. Some compounds of silver are light-sensitive, making silver important in the manufacture of photographic films and papers.

Tantalum. The metallic chemical element of atomic number 73, with symbol Ta, atomic weight 180.95, melting point 5, 462.6°F (3, 017°C), and boiling point of 9, 797 ±212°F (5, 425 ±100°C). Tantalum is a heavy, gray, hard metal that is used in alloys to pen points and analytical weights.

Technetium. The metallic chemical element of atomic number 43, with symbol Tc and atomic weight 98. Technetium was the first element to be produced synthetically; scientists have never detected the natural presence of this element on Earth.

Tellurium. The nonmetallic chemical element of atomic number 52, with symbol Te, atomic weight 127.60, melting point 841.1 ± 32.54°F(449.5 ±0.3°C), and boiling point 1, 813.64 ±38.84°F (989.8 ±3.8°C).

Tellurium is a grayish-white, lustrous, brittle metal. It is a semiconductor and is used in the electronics industry.

Thallium. The metallic chemical element of atomic number 81, with symbol Tl and atomic weight 204.38. Thallium is a bluish-gray metal that is soft enough to be cut with a knife. Thallium sulfate is used as a rodenticide and ant poison.

Tin. The metallic chemical element of atomic number 50, with symbol Sn and atomic weight 118.69. Tin is alloyed with copper and antimony to make pewter. It is also used as a soft solder and as coating to prevent other metals from corrosion.

Titanium. The metallic chemical element of atomic number 22, with symbol Ti, atomic weight 47.90, melting point 3, 020 ±50°F (1, 660 ±10°C), and boiling point 5, 948.6°F (3, 287°C). This element occurs as a bright, lustrous brittle metal or dark gray powder. Titanium alloys are strong for their weight and can withstand large changes in temperature.

Tungsten. The metallic chemical element of atomic number 74, with symbol W, atomic weight 183.85, and melting point 6,170 ±68°F (3,410 ±20°C). The melting point of tungsten is higher than that of any other metal. Its chief use is as a filament in electric light bulbs.

Vanadium. The metallic chemical element of atomic number 23, with symbol V and atomic weight 50.94. Pure vanadium is bright white. This metal finds its biggest use in strengthening steel.

Yttrium. The metallic chemical element of atomic number 39, with symbol Y, atomic weight 88.91, melting point 2, 771.6 ±46.4°F (1, 522 ±8°C), and boiling point 6, 040.4°F (3, 338°C). Yttrium is a relatively active metal that decomposes in cold water slowly and in boiling water rapidly. Certain compounds containing yttrium have been shown to become super-conducting at relatively high temperatures.

Zinc. The metallic chemical element of atomic number 30, with symbol Zn and atomic weight 65.39. Zinc—a brittle metal at room temperature—forms highly versatile alloys in industry. One zinc alloy is nearly as strong as steel, but has the malleability of plastic.

Zirconium. The metallic chemical element of atomic number 40, with symbol Zr, atomic weight 91.22, melting point 3, 365.6 ± 35.6°F (1, 852 ±2°C), and boiling point 7, 910.6°F (4, 377°C). Neutrons can pass through this metal without being absorbed; this makes it highly desirable as a construction material for the metal rods containing the fuel pellets in nuclear power plants.

See also Ammonia; Compound, chemical; Deuterium; Element, transuranium; Tritium; Valence.

Resources

BOOKS

Lide, David R. CRC Handbook of Chemistry and Physics. 86th ed. Boca Raton, FL: CRC Press, 2005.

Ede, Andrew. The Chemical Element: A Historical Perspective. Westport, CT: Greenwood Press, 2006.

Emsley, John. Nature’s Building Blocks: An A-Z Guide to the Elements. Oxford, UK: Oxford University Press, 2001.

Merck. The Merck Index. Whitehouse Station, NJ: Merck; London: Harcourt, 2001.

Scerri, Eric, R. The Periodic Table: Its Story and its Significance. New York: Oxford University Press, 2006.

Siekierski, Slawomir. Concise Chemistry of the Elements. Chichester, UK: Horwood Publishing, 2002.

Robert L. Wolke