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In developing the concept of electronegativity, Pauling
Chapter 9, Problem 61P(choose chapter or problem)
In developing the concept of electronegativity, Pauling used the term excess bond energy for the difference between the actual bond energy of X—Y and the average bond energies of X—X and Y—Y (see text discussion for the case of HF). Based on the values in Figure 9.20, p. 364, which of the following substances contains bonds with no excess bond energy?
(a) PH3
(b) CS2
(c) BrCl
(d) BH3
(e) Se8
Questions & Answers
QUESTION: Problem 61P
In developing the concept of electronegativity, Pauling used the term excess bond energy for the difference between the actual bond energy of X—Y and the average bond energies of X—X and Y—Y (see text discussion for the case of HF). Based on the values in Figure 9.20, p. 364, which of the following substances contains bonds with no excess bond energy?
(a) PH3
(b) CS2
(c) BrCl
(d) BH3
(e) Se8
ANSWER:
Problem 61P
Here we have to find out which of the following substances contains bonds with no excess bond energy.
The excess bond energy is defined as the difference between the actual bond energy for an X-Y bond and the average of the energies for the X-X and Y-Y bonds.
It can be expressed as, Excess bond energy = BE X-Y - ½ (BE X-X + BE Y-Y )
When the atom X and Y are identical or having same electronegativity, then the excess bond energy will be zero.
Step 1
(a) PH3
The electronegativity (EN) of P =2.1 EN of H = 2.1
Thus due to same electronegativity of P and H, the excess bond energy of PH3 is zero.