Chemistry

Noble Gas

• any of the gaseous elements helium, neon, argon, krypton, xenon, and radon, occupying Group 0 (18) of the periodic table. They were long believed to be totally unreactive but compounds of xenon, krypton, and radon are now known.

Oxidation number

• a number assigned to an element in chemical combination that represents the number of electrons lost (or gained, if the number is negative) by an atom of that element in the compound.

Valence electron

• one of the outer shells of an atom that can participate in forming chemical bonds with other atoms.

Semimetal

• a material with a very small overlap between the bottom of the conduction band and the top of the valence band

Nonmetal

• an element or substance that is not a metal.

Alkaline Earth metals

• any of the elements beryllium, magnesium, calcium, strontium, barium, and radium, occupying Group IIA (2) of the periodic table. They are reactive, electropositive, divalent metals, and form basic oxides that react with water to form comparatively insoluble hydroxides.

Transition metals

• any of the set of metallic elements occupying a central block (Groups IVB–VIII, IB, and IIB, or 4–12) in the periodic table, e.g., iron, manganese, chromium, and copper. Chemically they show variable valence and a strong tendency to form coordination compounds, and many of their compounds are colored.

Family

• as it relates to taxonomic rank, is between order and genus. Family, then, designates a category of classification that is fairly precise

Element

• each of more than one hundred substances that cannot be chemically interconverted or broken down into simpler substances and are primary constituents of matter. Each element is distinguished by its atomic number, i.e., the number of protons in the nuclei of its atoms.

Period

• A period is the name given to a horizontal row of the periodic table. The periodic table has seven periods. Period 1 contains only two elements: hydrogen and helium.

Periodic Table

• a table of the chemical elements arranged in order of atomic number, usually in rows, so that elements with similar atomic structure (and hence similar chemical properties) appear in vertical columns.

Metalloid

• an element (e.g., germanium or silicon) whose properties are intermediate between those of metals and solid nonmetals. They are electrical semiconductors.

Mass Number

• the total number of protons and neutrons in a nucleus.