We're told the subatomic world operates differently from the classical laws that we experience in our everyday life. The world of the atoms can seem strange and counterintuitive, governed by probability. Still, we can't help but see parallels when we try to grasp their world through the lens of our own. We find patterns that feel familiar to make sense of their discrete world.
What we see are electrons arranged hierarchically, some shunned to the outer confines of the atom, away from the cozy attraction to the nucleus.
These electrons, which are present in the atoms' outermost shells, also desire other companion electrons to form bonding partners.
In the words of G.N. Lewis, an atom can find stability when its outer shell can accommodate eight electrons. Carbon, Nitrogen, Oxygen, and Halogens take the rule of 8 very seriously. These atoms attempt to form covalent bonds, allowing each combining atom to retain eight electrons by sharing.
Chemistry determines the number of bonds these atoms can form, known as their valencies. Therefore, carbon can form four bonds, nitrogen three, oxygen two, and halogen one bond.
However, there are valence electrons in the outermost shell that rebel. They don't take part in any bond-forming interactions, and these recluses get labelled as the lone pair. Nitrogen can have one, oxygen two, and halogens three lone pairs, which are denoted as dots over the atom's symbol.
But recluse doesn't mean timid. They are controlling, bending a molecule's shape, by increasing repulsive interactions. Also reactive, when necessary.
They are known to donate their electron density to atoms deficient in electrons, belonging to a group called electrophiles. By doing so, they form a new covalent bond with the electrophiles, but they do it in their own terms.
In the language of chemistry, the lone pair are an atom's valence shell electrons that took part in hybridization but evaded the covalent bond formation with other atoms. So, the atom now has two sets of outer electrons: bonding electrons and non-bonding electrons, also referred to as lone pairs.
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Chapter - Fundamentals of Organic Reactions
