Question

for each pair of covalently bonded atoms, choose the one expected to have the shortest bond length.
(a) c-br
(b) c-i (a,b)
(c) n≡n
(d) n-n (c,d)
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Explanation:

For Pair (A,B) (C-Br vs C-I)

Step1: Recall bond length factors

Bond length is related to atomic radius. Larger atomic radius leads to longer bond length.

Step2: Compare Br and I radii

Bromine (Br) has a smaller atomic radius than Iodine (I) (as we move down a group, atomic radius increases; I is below Br in Group 17).

Step3: Determine shorter bond

Since C - Br involves Br (smaller radius than I in C - I), C - Br bond length is shorter. So for (A,B), the answer is A. C - Br.

For Pair (C,D) (N≡N vs N - N)

Step1: Recall bond order effect

Bond order (number of bonds between atoms) affects bond length. Higher bond order means shorter bond length.

Step2: Compare bond orders

N≡N has a bond order of 3, while N - N has a bond order of 1.

Step3: Determine shorter bond

Since N≡N has a higher bond order (3 > 1), its bond length is shorter. So for (C,D), the answer is C. N≡N.

Answer:

For (A,B): A. C - Br
For (C,D): C. N≡N