All terms in this list:

atom: A theoretical particle of matter, imagined to be incapable of further division; the smallest possible unit of substance.

Element: Any one of the simplest chemical substances that cannot be decomposed in a chemical reaction or by any chemical means and made up of atoms all having the same number of protons.

Compound: composed of elements; not simple

proton: A positively charged subatomic particle forming part of the nucleus of an atom and determining the atomic number of an element; the nucleus of the most common isotope of hydrogen; composed of two up quarks and a down antiquark

Electron: The subatomic particle having a negative charge and orbiting the nucleus; the flow of electrons in a conductor constitutes electricity.

neutron: A subatomic particle forming part of the nucleus of an atom and having no charge; it is a combination of an up quark and two down quarks

nucleus: The core, central part (of something), round which others are assembled.

electron cloud: A mathematically defined region around an atomic nucleus defined by a high probability that the atom's electrons will be present in that region.

atomic number: The number, equal to the number of protons in an atom that determines its chemical properties. Symbol: Z

mass number: The total number of protons and neutrons in an atomic nucleus.

periodic table: A tabular chart of the chemical elements according to their atomic numbers so that elements with similar properties are in the same column.

nonmetal: an element, such as phosphorus or chlorine, that does not have the chemical or physical properties of a metal

chemical symbol: A shorthand way of representing an element.

metal: Any of a number of chemical elements in the periodic table that form a metallic bond with other metal atoms; generally shiny, somewhat malleable and hard, often a conductor of heat and electricity.

average atomic mass: The weighted average of the atomic masses of the naturally occurring isotopes of an element.

metalloid: an element, such as silicon or germanium, intermediate in properties between that of a metal and a nonmetal; especially one that exhibits the external characteristics of a metal, but behaves chemically more as a nonmetal

group: A set with an associative binary operation, under which there exists an identity element, and such that each element has an inverse.

period: A length of time.