Which bonds is stronger?

Question

Which bongs will be stronger, those between hydrogen and C, N, O, and F on the one hand or those between hydrogen and Si, P, S, and Cl on the other?

Within the first group, bond strength goes in this order: HF>OH>NH>CH. Why?

Answer 1

In general, the first-row elements form the strongest bonds. This is because they have the smallest atoms, so that orbital overlap can occur more effectively.

C-H: 413 kJ/mol     Si-H: 324 kJ/mol (calculated)

N-H: 391 kJ/mol     P-H: 297 kJ/mol (internet); 321 kJ/mol (calculated)

O-H: 366 kJ/mol     S-H: 347 kJ/mol

F-H: 568 kJ/mol     Cl-H: 427 kJ/mol

Note however that this HF>OH>NH>CH observation is not correct.

Answer 2

The strength of the bonds between hydrogen and a nonmetal is based partly due to the electronegativity of the nonmetal. The more electronegative the nonmetal is, the stronger the bond will be. This is because hydrogen acts similar (but to a lesser extent) to an alkali metal when bonded in this way. That is why bonds with C, N, O and F will be stronger than Si, P, S and Cl. It is also the reason why HF>OH>NH>CH.