p-Block Elements Test - 4

Due to the lower values of electronegativities of bromine and iodine they cannot oxidize Pb⁺² to Pb⁺⁴.
However, chlorine is more electronegative and a stronger oxidizing agent than bromine and iodine.

Hence, PbCl₄ exists while PbBr₄ and PbI₄ do not.

The oxidizing power of XO₂ (X = C, Si, Sn or Pb) increases as the group is descended. PbO₂ can oxidize conc. HCl to Cl₂ but SnO₂ and SiO₂ cannot. This is because the stability of the +2 oxidation state increases down the group due to the inert pair effect.

Among the elements of the p-block of the periodic table, stability of lower oxidation state increases down the group because of the inert pair effect.

The two most common oxidation states exhibited by the elements of the group 14 are +2 and +4 and the stability of the +2 oxidation state increases down the group.

Hence, the order of stability of the dihalides of Si, Ge, Sn and Pb is:
SiX₂ << GeX₂ << SnX₂ << PbX₂.

Chain silicates are formed by the sharing of two oxygen atoms by each tetrahedron. Anion of chain silicates can be represented as (SiO₃)_n^2-.

SO₄^2-, NH₄⁺ and PO₄^3- are sp³ hybridized having tetrahedral geometry, but SCl₄ is sp³d hybridized having a distorted triangular bipyramidal geometry (see-saw shape).

It can only form a dimer.

Ca₂B₆O₁₁ + 2Na₂CO₃ -----Heat-----» Na₂B₄O₇ + 2NaBO₂ + 2CaCO₃↓

Boric acid is soluble in boiling water. When heated above 170°C, it dehydrates, forming metaboric acid (HBO₂).
H₃BO₃ → HBO₂ + H₂O

Metaboric acid is a white, cubic crystalline solid and is only slightly soluble in water. Metaboric acid melts at about 236°C and when heated above about 300°C, it further dehydrates, forming tetraboric acid or pyroboric acid (H₂B₄O₇).
4HBO₂ → H₂B₄O₇ + H₂O

Further heating leads to formation of boron trioxide.
H₂B₄O₇ → 2B₂O₃ + H₂O