What is an ionic bond?
By definition, an ionic bond is a chemical bond that forms between two or more oppositely charged ions. The animation above shows an ionic bond between a magnesium ion and two chlorine ions. There are three main concepts to know in order to understand how, and why, ionic bonds form.
The first concept to understand is that atoms "want" to obtain a full outermost electron orbital. This is due to the octet rule, and causes some atoms to donate electrons to other atoms, while some atoms accept electrons from other atoms. This donating and accepting of electrons allows atoms to achieve a full outer electron octet, which is the most chemically stable configuration .
The second concept to understand is that, once formed, the atoms, which have gained or lost electrons, are now charged. This charge is either positive or negative, depending upon whether the atom has gained or lost electrons. Since the number of electrons and protons in a neutral atom is equal, ions are charged due to having extra or fewer electrons than they have protons. Atoms which donate electrons (lose negatively charged particles) become positively charged (fewer electrons than protons). Atoms which gain electrons become negatively charged (more negative electrons that positive protons).
The third concept to know is that oppositely charged ions are attracted to each other (see animation below), while ions with like charges (the same charge) repel each other, and can not form a chemical bond.
Ions attracted to each other form a weak chemical bond known as an ionic bond. This bond is much weaker than a covalent bond, in which the atoms share the electrons.