Look for the specific bonds and the atomic radii , We will assume that the bond lengths are the sum of the radii of the atoms involved.Thus, we predict
C-S bond length = radius of C + radius of S = 0.77 A + 1.02 A = 1.79 A
C-H bond lenght = 0.77 A + 0.37 A = 1.14 A
S-H bond length = 1.02 A + 0.37 A = 1.39 A
The experimentally determined bond lengths in methyl mercaptan are C-S = 1.82 A , C-H = 1.10 A , ans S-H = 1.33 A .
In general, the lengths of bonds involving hydrigen show larger deviations from the values predicted by the sum of atommic radii than do those bonds involving larger atoms.
C-S =1.79 A,