Question

5a. Compare the structures in Group A where the central atoms are in the same group of the periodic table (i. e., SiH4 and CH4, NH3 and PH3, and H2O and H2S). What structural similarities do you see for elements in the same group? b. Now consider the compounds containing P and S using expanded octet. What structural differences do you observe for compounds where the central atoms are in the same group in the periodic table? How are these differences explained in Lewis theory? In valence bond theory? c. How do you expect the chemistry of the elements to change descending a group, given the different structures available to the heavier elements?

Answer 1

similarly in H2O and H2S also bond lengths, bond angles and dipole moments vary.

Consider PCl5 and SF6 molecules.

Both the molecules contain more than 8 electrons around their central atoms. This type of molecular structures and their geometry is not explained by Lewis theory.

Consider PCl5 :-

According to Valence bond theory in the central atom P there are 5 unpaired electrons in its excited state.

P:(Ne) 3s13px1 3py1 3pz1 3d1

These 5 unpaired overlap with the 3p orbitals of Cl to form the sigma bonds.

But this theory failed to explain the same bond lengths of all the P-Cl bonds.

c. Along the group from top to bottom heavier elements show inert pair effect that is reluctance of s- electrons to participate in bond formation.

For example, in IVA group Pb mostly shows +2 oxidation state rather than +4 oxidation state.