There are three types of strong chemical bond: ionic, covalent and metallic. All three are explained by electrostatic forces, which are the attractions between opposite charges.
In ionic bonding the particles are oppositely charged ions. Electrons are transferred from one atom to another. Ionic bonding occurs in compounds formed from metals combined with non-metals, such as sodium chloride.
In covalent bonding the particles are atoms that share pairs of electrons. Covalent bonding occurs in most non-metallic elements, such as oxygen, and in compounds of non-metals, such as water.
In metallic bonding the particles are atoms that share delocalised electrons. Metallic bonding occurs in metallic elements and in alloys.