Ionic Bonds and Ionic Compounds

When two atoms with large differences in electronegativity react, there is a complete transfer of
electrons from the less electronegative atom to the more electronegative atom. The atom that loses
electrons becomes a positively charged ion, or cation, and the atom that gains electrons becomes a
negatively charged ion, or anion. In general, the elements of Groups I and II (low electronegativities)
bond ionically to elements of Group VII (high electronegativities). Elements of Groups I and II
(metals) give up their electrons to form cations that have a noble gas configuration, while Group VII
elements gain an electron to form anions with the noble gas configuration. For example, a neutral
sodium atom has one valence electron in the 3s subshell, whereas a neutral chlorine atom has seven
valence electrons. If sodium sheds itself of its valence electron, it will possess the same electronic
configuration as neon, a noble or inert gas with a filled octet. Conversely, chlorine is one electron
short of a stable octet: If it gains an extra electron, it will have the electronic configuration of argon.
When the two come together, then sodium loses an electron to chlorine:

Na  +   Cl  →   Na+ Cl–

Since opposite charges attract, these two are now held together by electrostatic forces and form the
compound we know as sodium chloride, or salt. This force of attraction between the charged ions is
called an ionic bond.

BASIC CONCEPTS

ionic   bond: transfer  of  electron(s)

covalent    bond: sharing   of  electron(s)

As seen from the example above, ionic compounds are formed by the interactions of cations and
anions. The nomenclature, or naming, of ionic compounds is based on the names of the component
ions. The following are some general guidelines: