The negative ion that results when an atom gains one or more electrons. An anion (pronounced "AN-ie-un") of an element is never called, for instance, the chlorine anion. Rather, an anion involving a single element is named by adding the suffix -ide to the name of the original element—in this case, "chloride." Other rules apply for more complex anions.
The number of protons in the nucleus of an atom. Since this number is different for each element, elements are listed on the periodic table of elements in order of atomic number.
A one-or two-letter abbreviation for the name of an element.
A term describing an element that exists as molecules composed of two atoms. All of the halogens arediatomic.
The use of an electrical current to cause a chemical reaction.
The length of time it takes a substance to diminish to one-half its initial amount.
Group 7 of the periodic table of elements, including fluorine, chlorine, bromine, iodine, and astatine. The halogens are diatomic, and tend to form salts; hence their name, which comes from two Greek terms meaning "salt-forming."
An atom that has lost or gained one or more electrons, and thus has a net electric charge.
A form of chemical bonding that results from attractions between ions with opposite electricalcharges.
Atoms that have an equal number of protons, and hence are of the same element, but differ in their number of neutrons. This results in a difference ofmass. Isotopes may be either stable or unstable—that is, radioactive.
A chart that shows the elements arranged in order of atomic number. Vertical columns within the periodic table indicate groups or "families" of elements with similar chemical characteristics.
A large molecule containing many small units that hook together.
A term describing a phenomenon whereby certain materials are subject to a form of decay brought about by the emission of high-energy particles. "Decay" in this sense does not mean "rot"; instead, radioactive isotopes continue to emit particles, changing into isotopes of other elements, until they becomestable.
A compound formed by the reaction of an acid with a base. Salts are usually formed by the joining of a metal and a nonmetal.
Electrons that occupy the highest energy levels in anatom, and are involved in chemical bonding. The halogens all have seven valence electrons.
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