Most metals are found in nature combined with nonmetals such as oxygen or sulfur. Notable exceptions are gold, platinum and silver. All the noble gases exist in nature uncombined and in the monoatomic form. Other gases that exist in the diatomic form are H2, O2, and N2. When neutral atoms lose or gain electrons, they form ions.
Cations are positive ions formed by the loss of electrons.
Anions are negative electrons form by the gain of electrons. Oxygen tends to gain two electrons and forms the O -2 anion. When the two ions combine, they do so in such a way so as to neutralize each other's charge.