Question

The silicon monosulfide diatomic molecule (SiS(g)) has a bond
dissociation enthalpy (BDE) of 619 kJ mol^-1 , an inter-nuclear distance of
193 pm and an electronic dipole moment ( el ) of 1.73 Debyes.
a) Calculate the partial ionic character for SiS(g).

b) Compare the molecular orbital descriptions for the bonding in SiS (g)
Si₂ (g) and S₂ (g).

Answer 1

Given, dipole moment (observed) = 1.73 Debyes = 1.73 X 3.33564 X 10⁻³⁰ C·m = 5.77 X 10^-30 C.m

We know that dipole moment = electronic charge X interatomic distance

Now if the bond is 100% polarized then, dipole moment (100%) = (1.6 X 10⁻¹⁹) C X (1.41 X 10⁻¹⁰) m = 2.26 X 10⁻²⁹ C m

ionic character = dipole moment (observed) /dipole moment (100%) = (5.77 X 10^-30) / (2.26 X 10⁻²⁹) = 0.26

% ionic character = 0.26 X 100 = 26%

For question b), it is too long to describe here. You need to draw three molecular orbital diagrams and probably you will also need to calculate the bond orders.