What is an ION?
Ions are particles with a charge. Theses particles can be individual atoms (monatomic) or groups of atoms (polyatomic). Ions can either be positively charged cations or negatively charged anions. Ions form when electrically neutral particles either gain electrons or lose electrons. Electrons are negatively charged subatomic particles. When an atom or group or atoms gains or loses electrons, the electrical balance in the particle is changed.
Monatomic ions form from individual atoms. Metallic atoms form ions by losing electrons. An atom has an equal number of positive protons in its nucleus and negative electrons in its electron cloud. When an metallic loses electrons, it is left with an excess positive charge because there are more protons than electrons. The atom is now a positive ion; a cation.
Polyatomic ions are groups of atoms that are held together by sharing electrons. (a covalent bond) These groups of atoms are not considered to be a compound because they have a net charge.