Chemical Bonding And Molecular Structure

Step 1: Consideration of electronic configuration.
The ability of an element to form complexes with coordination numbers greater than 4 depends on the availability of vacant d-orbitals. Silicon (Si) has vacant 3d orbitals that can participate in bonding, allowing it to form with a coordination number of 6.
Step 2: Carbon’s limitation.
Carbon (C), however, does not have vacant d-orbitals. This limits its ability to extend its coordination number beyond 4. As a result, is not stable and does not exist.
Step 3: Comparing atomic radii.
Although the atomic radius of Si (1.17 ) is larger than C (0.77 ), the key reason for the stability of is the availability of the 3d orbital in Si, not just the difference in atomic radii.
Conclusion:
The correct explanation is that carbon lacks the 3d orbitals, whereas silicon possesses vacant 3d orbitals that enable it to form complexes like .

The formula for estimating the percentage ionic character is: Where: is the observed dipole moment (given as 2 D), is the ideal dipole moment if the molecule were 100% ionic, calculated as: Where:
is the charge of the ions , is the internuclear distance .
Now, calculating the ideal dipole moment: Now, the percentage ionic character is: