Notes

An ion is an electrically charged atom (or group of atoms) formed when the atom gains or loses electrons. An atom is always electrically neutral, as the number of protons within its nucleus equals the number of electrons surrounding the nucleus. When an atom gains or loses electrons while combining with other atoms, it is no longer neutral because the number of electrons becomes either less or more than the number of protons. So, the atom converts into an electrically charged ion. Depending on its charge, it's either an anion (negatively charged) or a cation (positively charged).
Anions are negatively charged ions. When an atom gains electrons, it ends up with more electrons than protons. So, the net charge of the atom, which is now called an anion, is negative. The suffix -ide is used to name an anion; for example, chlorine forms the chloride ion.
Nonmetals have more than three valence electrons in their outer shell. It's easier for a nonmetal to gain electrons than to lose electrons, so nonmetals tend to form anions. For example, chlorine (Cl) has seven valence electrons in its neutral state. It gains one electron to complete its octet and forms a chloride ion (ClÈ). Chlorine can also form an octet by losing seven electrons, but since it's easier for it to gain one electron than to lose seven, it's more likely to form an anion.
Cations, on the other hand, are positively charged ions. When an atom loses electrons, it ends up with fewer electrons than protons. So, the net charge of the atom, now called a cation, is positive. A cation takes the same name as the element; sodium, for example, forms the sodium ion.

Most metals have one, two, or three valence electrons in the outer shell. Losing those electrons requires less energy than gaining enough electrons to reach noble gas stability. So, metals tend to lose electrons and form cations. For example, sodium (Na) has one valence electron in its neutral state. It loses one electron to attain an octet and forms a sodium ion (NaÄ). Sodium can also form an octet by gaining seven electrons, but since it's easier for it to lose one electron than to gain seven, it's more likely to form cations.

Metallic bonds occur only between metal atoms. Metals are made up of cations, and electrons drift freely among these cations.