Question

Which of the following chemical bonds has the most ionic character?
(A) $LiH$
(B) $HF$
(C) $CsH$
(D) $HI$

Answer 1

Hint:Ionic character of a compound is determined by the difference between the electronegativity of the constituent atoms. A species has a greater ionic character if the difference between the electronegativity between the two atoms is close to $2$.

Complete answer:
The given compounds are all covalent compounds but they must have some ionic character. In order to check the ionic character of these compounds we have to check the parameter of fajan’s rule. These are;
Polarizing power of an atom is defined as the ability of a cation to attract the electron cloud towards itself. It is proportional to charge and size.If the size is small, then the cation will have more charge density and hence its polarising power increases whereas in anions Polarisability decreases with the increase in size. Also, higher the charge on a cation more is its polarizing power while higher the charge of an anion more is its polarizability. High polarising power means more covalent character.
So, according to the rule, larger the size of the cation, greater will be its ionic character. Among the given options $Cs$ has the greatest size thus, has the highest electropositive character. Also, the radius of hydride and iodide anion are nearly the same. Therefore, $HI$ will be less ionic than $CsH$ While Covalent character of $HF$ and $LiH$ is very high due to the difference in their electronegativity.
Thus, $CsH$ will have the most ionic character

Therefore, option (C) is correct.

Note:
According to Fajan rule no compound is completely covalent or completely ionic. Every covalent compound has some ionic character while every ionic compound has some covalent compound.