Question

C-F bond energy us 485 KJ/mol and has bond length of 1.35A. Si-F bond energy is 565 KJ/mol and bond length of 1.6A.

A) Explain the difference in bond length

B) Rationalize why Si-F is stronger than the C-F bond.

Answer 1

A) The higher bond length of Si-F bond in comparison of C- F is due to the size difference of Si and C. Carbon belongs to the second period while Si belongs to third and we know that size of the elements are decreasing down the group hence, size of Si is large in comparison of Carbon that makes Si-F bond length maximum.

B) The bond energy of C-F is less than Si-F because the difference in electronegativity between Si and F is large in comparison of C and F. Due to the large difference in electronegativity between Si and F, it form stronger bond hence bond enthalpy is maximum which results in large bond energy of Si-F.