The total mass of an atom, which is the mass in grams of 1 mole of the atom

One of several atomic forms of an element, each with the same number of protons but a different number of neutrons, thus differing in atomic mass

the number of protons in the nucleus of an atom, unique for each element and designated by a subscript to the left of the elemental symbol

An isotope (an atomic form of a chemical element) that is unstable; the

nucleus decays spontaneously, giving off detectable particles and energy

The outermost energy shell of an atom, containing the valence electrons in­volved in the chemical reactions of that atom

An energy level of electrons at a characteristic average distance from the nucleus of an atom.

An electron in the outermost electron shell

The three-dimensional space where an electron is found 90% of the time

A single covalent bond; the sharing of a pair of valence electrons by two atoms

An attraction between two atoms, resulting from a sharing of outer-shell electrons or the presence of opposite charges on the atoms

A type of strong chemical bond in which two atoms share one or more pairs of valence electrons

A double covalent bond; the sharing of two pairs of valence electrons by two atoms

Two or more atoms held together by covalent bonds

The attraction of a given atom for the electrons of a covalent bond