"Valence"

Valence describes how many outer shell electrons an element presents for chemical reactions. A valence can theoretically range from -7 to zero to +7, and is notated in chemical equations with superscripted '+' or '-' signs. This can be helpful in understanding and predicting reactions and balancing chemicals equations because the elements comprising a compound will be in ratios such that the combined valences equal zero.

If this was too big a leap, please review our FAQ on Faraday's Law first, which starts with the very basics. Otherwise, examples will clarify ...

Hydrogen and Chlorine can be combined to form hydrochloric acid:
H⁺ + Cl^- = HCl

Nickel and two parts of Chlorine can be combined to form nickel chloride:
Ni⁺⁺ + 2Cl^- = NiCl₂

Radicals are combinations of atoms so strongly bonded together that we treat them as a single unit in most chemical reactions, and radicals have a valence. For example :

OH^- is the hydroxide radical, SO₄^{- -} is the sulfate radical

Sodium and hydroxide can be combined to form caustic soda
Na⁺ + OH^- = NaOH

Copper and sulfate can be combined to form copper sulfate Cu⁺⁺ + SO₄^{- -} = CuSO₄