Atoms are electrically neutral as a result of having an equal amount of positive (due to the protons) and negative (due to the electrons) charges on it.
An ion generally is an electrically unbalanced atom (i.e an atom with a net charge on it)
A negative ion called an anion is produced when an atom gains an extra electron from a neighboring atom, giving it an extra negative charge. This can be produced by ionization with a radioactive radiation or simply by dissolution.
A positive ion is called a cation and it is produced when an atom loses electron to a neighboring atom. The loss of this electron causes the positive charges to outweigh the negative charges in the atom. Cations can be produced by radioactive radiation ionization of an atom or by simple dissolution.
The subatomic particle that is negative is the 'electron'.
