Atoms lose their neutrality when electrons are either lost or gained. Atoms that have lost or gained electrons are called ions. Neutral atoms have the same number of protons, neutrons and electrons.
Protons have a positive charge, while electrons have a negative charge. Ions are electrically charged atoms, having a negative charge if they gained an electron and a positive charge if they lost an electron. The chemical and physical properties of an atom change as ions are created. When two ions with opposite charges come into contact, they are attracted to each other. They may begin to share electrons in either covalent or electrovalent bonds.