What are ions? What substances are made of ions? Is diffusion typical for which substances?

An ion is a charged atom or molecule. It is charged because the number of electrons is not equal to the number of protons in an atom or molecule. An atom can acquire a positive charge or a negative charge, depending on whether the number of electrons in the atom is greater or less than the number of protons in the atom.

When an atom is attracted to another atom because it has an unequal number of electrons and protons, the atom is called an ion. If an atom has more electrons than protons, it is a negative ion, or anion. If it has more protons than electrons, it is a positive ion.