Question

According to Hannay-Smith formula, if E.N. difference between A and B is $2.1$, then A-B molecule is expected to have x% ionic character. Find ${\displaystyle \frac{x}{10}}$ value to the next integer.

Answer 1

Hint:We know that bonds formed between two atoms are either covalent or ionic. Ionic bond involves the complete transfer of electrons while covalent bond involves the sharing of electrons. However, none of the bonds is perfect. All ionic bonds have some covalent character and all covalent bonds have some ionic character, i.e., the electrons are not shared perfectly.
Formula used: Hannay- Smith formula:
$x=16\left(X_A-X_B\right)+3.5{\left(X_A-X_B\right)}^2$
Where, $x$ is the percentage of ionic character in the A- B bond.
And, $X_A$ and $X_B$ are the electronegativities of A and B respectively.

Complete step by step answer:
When the atoms forming the covalent bond are different, their electronegativities are bound to be different and both attract the shared pair of electrons with different strengths. The electron cloud density is shifted more towards the more electronegative atom leading to partial separation of charges in the bond. Hence, the bond is not 100% covalent and develops some ionic character as a result.
In the given compound A- B, we are given the electronegativity difference between the two atoms. Thus, we can calculate the percentage ionic character in the compound using the Hannay- Smith equation which is given as $x=16\left(X_A-X_B\right)+3.5{\left(X_A-X_B\right)}^2$
Substituting the values, we get, $x=16\left(2.1\right)+3.5{\left(2.1\right)}^2$
$\Rightarrow x=49\mathrm{\%}$
$\therefore {\displaystyle \frac{x}{10}}=4.9$

The next integer value and the answer is 5.

Note:
When a covalent bond is formed between two atoms of the same element, the electrons are shared and attracted equally by both the atoms. Thus, the bond is 100% covalent. This is possible because the two atoms are identical and have same electronegativities, thus, pulling the electrons towards themselves with equal tendency.