Every reaction is based on the exchange or sharing of electrons. The main alternatives are:

• donating and receiving outer electrons, resulting in Ionic bonding​
• sharing outer electrons, resulting in Covalent bonding​

These two make for distinctively different kinds of substances, the specifics of which form a basis for understanding chemistry. The more sophisticated ones, like Hydrogen bonding​, expand on these notions of electromagnetic interaction, one of the Rules for the universe​.