Question

The decreasing order of electronegativity among hybridised carbon atoms is
A. $sp > s{p^2} > s{p^3}$
B. $s{p^3} > s{p^2} > sp$
C. $sp > s{p^3} > s{p^2}$
D. $s{p^2} > s{p^3} > sp$

Answer 1

Hint: The electrons in the s-orbital are present closer to the nucleus. As a result, they experience a stronger force of attraction. When we consider hybrid orbitals, greater the s-character more will be its electronegativity.

Complete answer:
In order to find the decreasing order of electronegativity, we need to determine the s-character of these hybrid orbitals one by one. Let us begin with sp hybrid orbital. One s-orbital and one p-orbital hybridise to make one sp hybrid orbital. So we can say that the s-character is $50\% $
Now, let us move on to $s{p^2}$ orbital. In this case, one s-orbital undergoes hybridisation with two p-orbitals. We can determine the s-character as $\dfrac{1}{3} \times 100$ where the numerator contains the number of s-orbitals and the denominator contains the total number of s and p orbitals that are taking part in hybridisation. So in $s{p^2}$ orbital, the s-character is $33.33\% $.
Consider $s{p^3}$ hybrid orbital. Here, one s-orbital undergoes hybridisation with three p orbitals, so the total number of orbitals is $1 + 3 = 4$ . Hence, the s-character can be calculated as $\dfrac{1}{4} \times 100 = 25\% $.
So we have now calculated the s-character of $sp, s{p^2}, s{p^3}$ hybrid orbitals to be $50\% ,33.33\% ,25\% $ respectively. Greater the s-character, stronger will be the force of attraction exerted by the nucleus due to the s-orbitals being present close to the nucleus. That is, the hybrid orbitals having a greater s-character will be able to strongly pull the shared pair of electrons in a chemical bond towards themselves. Hence we say, greater the s character greater will be the electronegativity. So the decreasing order of electronegativity of the hybrid orbitals is $sp > s{p^2} > s{p^3}$ that is, option (A).

So, the correct option is A).

Note: Electronegativity is the ability to pull the shared pair of electrons towards itself in a chemical bond. Stronger the force of attraction exerted by the nucleus, greater will be the electronegativity. While answering such objective type questions observe and analyse the options carefully to avoid errors.