Amphoteric: A compound that reacts as a weak acid or a weak base.

Atomic Weight: The atomic weight of an element is the average relative weight of an element referred to Carbon 12 as the standard.

Atomic Number: It is an experimentally determined number characteristicof a chemical element that represents the number of protons in the nucleus which in a neutral atom equals the number of electrons outside the nucleus.

Covalent: The ability to form a bond in which two atoms share a pair of electrons.

Ductile: A substance is considered to be ductile, if it can be hammered out thin or drawn into a wire.

Electronegative: The tendency to gain electrons; non-metallic; acid.

Electropositive: The tendency to lose electrons; metallic; basic.

Halogen: Halogen means salt producer; Sea salts are compounds of halogens with metals.

Hydroxides: Any compound consisting of an element orradical combined with one or more hydroxyl radicals (OH - one oxygen atom combined with one hydrogen atom).

Isotopes: Two or more species of atoms having the same atomic number (number of protons)but with differing mass numbers (number of protons and neutrons), i.e., they differ in the number of neutronsin the nucleus. Isotopes have nearly the same chemical properties but may differ in physical properties.

Monoatomic: Occurs as a single atom rather than in pairs or in combination.

Oxidation State: The state of an element in a compound with respect to the number of electrons it has lost or gained, expressed as a positive or negative number indicating the ionic charge of an atom and equal to its valence.

Oxidizing: Change in the state of the atoms or ions of an element to a higher positive state by the loss of electrons. An oxidizing agent is an element that can remove electrons to another element.

Reducing: Change in the state of the atoms or ions of an element to a lower positive state by the gain of electrons. A reducing agent is an element that can add electrons to another element.

Valence Electrons: The electrons in the outermost shell of an atom.

Period: A horizontal row in the periodic table. Each period begins filling a new electron shell.