Chemical Element
A chemical element is a substance that cannot be changed, broken down, or decomposed by ordinary chemical or physical methods into a simpler form. A chemical element is composed of atoms, identical and unique for every element, that vary only in their mixture of protons, neutrons, and electrons.
The number of elements known to scientists constantly changes as advances in technology allow the synthesis of heavier elements. As of 2000, the International Union of Pure and Applied Chemistry (IUPAC), an international scholarly scientific organization with the responsibility for naming elements, had named elements as heavy as the element Meitnerium (atomic number 109). Observations of heavier elements (up through atomic number 118) awaited confirmation. Of the recognized elements, 89 occur in a free or combined state in the Earth's crust. The remaining elements are prepared or synthesized in laboratories. Most of the natural elements are found in various combinations with each other as chemical compounds. Only a few of the elements, such as, gold, mercury, lead, silver, sulfur, and copper can be found in their pure state in nature.
The properties associated with the chemical elements differ enough that they are classified as two general classes, metals and nonmetals. Metallic elements are malleable, ductile, and good conductors of heat and electricity. Their luster allows them to reflect heat and light. Some examples of metals include gold, silver, copper, potassium, and zinc. At standard temperature and pressure, mercury is a liquid metal. Sulfur, iodine, and carbon are examples of solid nonmetallic chemical elements. These elements are poor conductors of heat and electricity, and are also brittle and dull in appearance. At standard temperature and pressure, bromine is a liquid nonmetal and nitrogen and oxygen are gaseous members of this class. Some elements are considered borderline because they display some characteristics of metals (such as, luster) and other properties associated with nonmetals (brittle). These elements are referred to as metalloids and include arsenic and germanium. Silicon, a metalloid, does not conduct heat and electricity as well as a metal, but is a better conductor than a nonmetal. These properties make it a good semiconductor for use in the computer industry.
The Swedish chemist, Jons Jakkob Berzelius (1779-1848) developed a system for representing each chemical element by a one or two letter symbol. These abbreviations are divided into three different types. The first type of symbol is derived from the first letter of the common name of the chemical element. Accordingly, the symbol for hydrogen is H, C represents carbon, and O represents oxygen. To provide for increasing numbers of elements, Berzelius suggested the use of a second letter representing the second letter of the chemical element or a letter whose sound is conspicuous when the name of the element is pronounced. Thus, calcium, represented by the symbol Ca and chromium, represented by the symbol Cr because of the predominant "r" in the pronunciation, represent a second class of element symbols. The final type of chemical symbol is derived from the Latin name for the element. The abbreviation for lead is Pb because the Latin name for lead is plumbum. The symbols for iron, Fe, and sodium, Na, come from the Latin ferrum and natrium. The first letter of an element's symbol is always capitalized and the second letter is normal or lower case. For example, the symbol for cobalt is Co, while CO represents carbon monoxide, a molecule composed of the elements carbon (C) and oxygen (O).
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