Also called electrovalent bond, an ionic bond is the electrostatic attraction existing between ions, forcing them to bond together. In other words, when an electron moves from one atom to the atom of another element, the atom losing the electron gets positively charged and the one gaining gets negatively charged. The atom that’s a part of the bond can lose or gain more than one electron. Both positively and negatively charged atoms are called ions; the positive ion called cation, and the negative ion being anion. As per the laws of attraction, positive attracts negative. And this attraction keeps the ionic bond intact.

Atoms attach to each other in different ways to make molecules; an ionic bond is just one of those routes. The majority of solid substances in the world such as rocks are solid because of an ionic bond. An ionic bond is usually a chemical bond between a metal and non-metal. The element donating an electron is often a metal, and the atom receiving the electron a non-metal. Potassium chloride (KCl), sodium fluoride (NaCl), sodium bromide (NaBr), etc. are ionic bonds. When two non-metals bond with each other, the connection is called a covalent bond. Similarly, the bonding between two metals is known as metallic bond.

Atom Stability

Why does an atom give away its electron? To comprehend this, one must understand the shells or energy levels encircling an atom’s nucleus. These shells are filled with electrons, and the shell farthest from the nucleus is called valence shell. The innermost shells always have required number of electrons; it’s the outermost shell that generally has issues with occupancy.

For instance, if an atom can house seven electrons in its valence shell, but has only six electrons, it will look to borrow one from another atom. Similarly, if the atom only has one electron in its outermost shell, it may part away with that lone electron, as letting go an electron is easier than finding six additional electrons.

When two atoms – one looking to borrow and the other keen to lend – meet, the electron movement between the atoms satisfies both atoms. As per the above example, the recipient atom completes its valence shell and the losing atom empties out the shell. The emptied shell vanishes and the second farthest shell becomes the new valence shell, which is now at full capacity. 

Atoms basically despise partially-filled valence shells because of stability issues. Generally, an atom is at optimal stability when its valence shell has eight electrons, like noble gases. The stability means the atom has sufficient binding energy to ensure the nucleus stays together and the atom doesn’t break apart.

Not all elements require eight electrons to be stable. For instance, the periodic table’s first five elements (hydrogen, helium, lithium, beryllium, and boron) need only two electrons to be stable. Besides being integrally sound, a stable atom need not bond or interact with other elements to exist and stay relevant.