Answer to Question #268565 in Inorganic Chemistry for shinal deo

Question

Compare and comment on the difference in the single-bond energies for the elements  of the second and third period of the following groups: group 14: C−C > Si−Si; but in Group 15: N−N < P−P; in Group 16: O−O <S-S and in group 17: F−F <Cl−Cl.          

Answer 1

$C-C \quad346kJ/mol\\ Si-Si \quad222kJ/mol\\ \quad\\ N-N \quad166kJ/mol\\ P-P\quad201kJ/mol\\ \quad\\ O-O \quad142kJ/mol\\ S-S \quad226kJ/mol\\ \quad\\ f-f \quad155kJ/mol\\ Cl-Cl \quad240kJ/mol\\$

The bond energy for a C-C bond is slightly greater than the Si-Si bond. This difference is reflected in the chemistry of silicon versus carbon compounds. The chemistry of carbon is dominated by catenation: the ability of a chemical element to form a long chain-like structure via a series of covalent bonds. Although silicon does form Si-Si bonds, they are far more reactive than their C-C analogues, and polymers of silicon are predominantly comprised of Si-O chains (as a result of the very strong bond).

P-P single bonds are stronger than N-N single bonds because phosphorus (EN = 2.19) is much less electronegative than nitrogen (EN = 3.04). Also, phosphorus can expand its valence shell to hold more than eight electrons, but nitrogen cannot.

O−O bonds are much weaker than S-S bonds because Sulphur is less electronegative and has access to d orbitals.

F−F bonds are much less weaker than Cl−Cl bonds due to screening effect of the fluorine atom$.$