An atom with no charge becomes positively charged when it loses an electron. When this happens, it is called a positive ion. If the atom gains an electron, the atom becomes a negative ion. In either case, the number of protons in the atom’s nucleus does not change. More than one electron can be removed from an atom to give it a positive charge of +2, +3 or more.
The addition and subtraction of negatively charged electrons can easily change an atom’s charge, because they perpetually spin in valence shells outside the nucleus. It is easier for a neighboring atom to share or steal an electron rather than a positively charged proton, which is found in the nucleus. It requires a strong energy input to split a proton free from other protons and neutrons.
Due to their chemical makeup, elements that are considered to be metals most easily lose electrons to become positive ions. Non-metals gain electrons and become negatively charged ions. Metals are organized on the periodic table into groups, which correspond to how many electrons they lose to become stable in their outermost valence shell. For example, aluminum (Al) is located in Group 3, and will lose three electrons to transform into an ion with a +3 charge.