Give reasons: (a) HCl is predominantly covalent in gaseous state. (b) KHF2 exists while KHCl2 does not. (c) Sigma bond is stronger than the pi bond. (d) NaCl gives white precipitate with silver nitrate solution.
(a) In HCl, the electronegativity difference in Cl and H atoms is 0.9. so it is predominantly covalent in gaseous state. (b) HF molecules are hydrogen bonded. Therefore, they can associate to form HF2 − anion which can exist in combination with potassium ion. (c) The strength of a covalent bond depends on the extent of the overlap. Greater the overlap, stronger is the bond. A sigma bond is formed by the axial overlap of the orbitals which is more effective than the sidewise overlap of pi bond as greater energy will be released in axial overlap. (d) Both NaCl and AgNO3 are ionic solids. They readily dissociate to form ions in the solution.
