Question

What is the lone pair of electrons? Explain with an example.

Answer 1

Unshared electrons in bonding are called lone pairs. Lone pairs are found in the outermost electron shell of atoms.

Complete answer:
A pair of electrons occupying an orbital in an atom or molecule and not directly involved in bonding is called lone pair. A lone pair refers to a pair of valence electrons that are not shared with another atom in a covalent bond and is sometimes called an unshared pair or nonbonding pair.
To calculate the lone pair first we have to calculate the number of hybrid orbitals or hybridization
The formula used to calculate lone pairs = ${\dfrac{Number\; of\; valence\; shell\; electrons\; of \;central\; atom - \; Number\; of\; electrons\; taking\; part\; in\; bonding}{2}}$...............................(i)

Let us use this formula to calculate the number of lone pairs.
Take the example of $Xe{F_2}$. Calculate the number of lone pairs in Xe. In this case Xe has eight electrons in the outermost shell and fluorine has seven electrons in the outermost shell. So two electrons of Xe and F are involved in formation of bonding with each other.
Thus, Number of valence shell electrons around central atom = 8
Number of electrons taking part in bonding = 2
Put the values in Equation (i),
Lone pairs = ${\dfrac{8 - 2}{2}}$ = $\dfrac{6}{2}$ = 3
Thus the number of lone pairs in Xe are = 3

Note: When a compound having lone pair then the bond angle decreases due to repulsion between lone pair and lone pair hence lone pair effect the geometry also. The lone pair - lone pair repulsions are maximum comparative to lone pair - bond pair and bond pair - bond pair.