Question

. a) Draw the Lewis structure of SO3 2- . b)- Identify the electronic and molecular geometries of the molecule, and the hybridization of the central atom. c) Is this molecule polar? Justify your answer by drawing the VSEPR molecular geometry and labeling the molecular dipole moment.

Answer 1

a) Lewis dot structure of SO₃^2- (Sulfite ion) : both sulphur and oxygen belongs to same oxygen family so both have same valence electrons.General electronic configuration is ns²np⁴ .

Valence electrons = 6+6+6+6-(-2) = 26

Formal charge = valence electrons - non bonding valence electrons - bonding electrons / 2

S = 6- 2 - 6/2 = +1

3O = 6 -6 -2/2 = -1

In 2nd structure : S = 6-2 -6/2 =0

                         O = 6 - 4 - 4/2 = 0

                         2O = 6 -6 - 2/2 = -1

In sulfite ion there are one S=O bond and two S-O bond.

These resonance structure are most stable even Sulphur atom have more than eight elcetrons due to less charge separation.

b) Hyberdisation ie used to explain molecular geometry.In sulfite ion central atom (least electronegative) is sp³ hyberdised.Sulfite ion have tetrahedral geometry (only bond pair electrons) and trigonal pyramidal shape (lone pair+ bond pair electrons). d- orbitals of sulphur does not involved in bonding.

c) Dipole monent: It is charge separation within a molecules due to electronegativity difference between different atoms within the molecules. In sulfite ion lone pair are not used to calculate dipole movement, only bonded pair electrons are used that is why there is net dipole movement in the downward direction because oxygen is more electronegative than sulphur.

For the calculation of dipole moment in sulfite ion: i) Draw lewis structure

ii) Draw 3D geometry (according to VSEPR theory lone pair are considered as a single area.In this theory valence electron keep themself maximum distance apart to avoid repulsion between electron.)

iii) non polar molecules have symmetrical distribution of charge and polar molecule have unsymmetrical distribution of charge.

Yes,sulfite ion have unsymetrical distribution of charge that is why it is polar molecule.