Atoms combine with one another to give compounds having properties different from the atoms they contain. The attractive force between atoms in a compound is a chemical bond. One type of chemical bond, called an ionic bond, is the force of attraction between oppositely charged species (ions) .

Ions that are positively charged are referred to as cations; those that are negatively charged are anions. Whether an element is the source of the cation or anion in an ionic bond depends on several factors, for which the periodic table can serve as a guide. In forming ionic compounds, elements at the left of the periodic table typically lose electrons, forming a cation that has the same electron configuration as the nearest noble gas. Loss of an electron from sodium, for example, gives the species Na, which has the same electron configuration as neon.


Ionic bonds are very common in inorganic compounds, but rare in organic ones. The ionization energy of carbon is too large and the electron affinity too small for carbon to realistically form a C4+ or C4+ ion. What kinds of bonds, then, link carbon to other elements in millions of organic compounds? Instead of losing or gaining electrons, carbon shares electrons with other elements (including other carbon atoms) to give what are called covalent bonds.