Chapter 10: The s-Block Elements

(i) Lithium and magnesium are both lighter and harder than the other metals in their respective groups.

(ii) Halides of both elements, LiCl and MgCl2 are soluble in ethanol.

These two elements have similar properties because of their similar atomic and ionic radii.

Beryllium oxide is amphoteric, unlike the other basic compounds.

(i) The thermal stability of the carbonates increases with increasing cationic size. The more stable the oxide of an alkaline earth metal, the less stable is the carbonate of the same. Hence BeCO3 is highly unstable as BeO is stable.

(ii) Alkali metals form oxides with oxygen and give metal oxides. The oxides will be basic except BeO because BeO is amphoteric. hey also react with water to form sparingly soluble hydroxides. As the size of the cations increase BeO and MgO have the highest lattice energy and they are insoluble in water.

BeSO4 and MgSO4 are readily soluble in water, CaSO4, SrSO4, and BaSO4 are insoluble. This is because the greater hydration enthalpies of Be2+ and Mg2+ ions overcome the lattice enthalpy factor and therefore their sulphate is soluble in water.

The alkali metal compounds form ionic compounds due to their large ionic size and low ionization enthalpy, while lithium forms compounds of covalent nature due to their small ionic size, high ionization enthalpy, and high electronegativity.

In the Solvay process, carbon dioxide is passed through a concentrated solution of sodium chloride saturated with ammonia, which forms ammonium carbonate followed by ammonium hydrogen carbonate. Ammonium hydrogen carbonate crystals separate and they are heated to form sodium carbonate. NH3 is recovered from the solution which contains NH4Cl is heated and treated with Ca(OH)2. The reaction of (NH4)2CO3 with NaCl gives two products, Na2CO3 and NH4Cl which are both soluble in water which does not shift the equilibrium to the right.

Oxygen atom with zero charges has 6 electrons, therefore the oxidation state is 0. When the oxygen atom has a negative charge, it has 7 electrons. Hence, the oxidation state is -1. The average oxidation state is 0 + (-1)/2 = -1/2.

Be and Mg electrons are tightly bound to the atom due to the small atomic and ionic size. The flame is due to the excitation of the electron from its energy states. The electrons of Be and Mgdo did not gain excitation from the energy provided by the flame. Hence they do not show any flame in the flame test.

The gaseous/vapour state is different than the solid-state. The structure of BeCl2 in the solid-state is a polymeric chain structure. BeCl2 tends to form a chloro-bridged dimer at temperatures below 1200K and dissociates into a linear monomer at high temperatures of the order of 1200 K.

IV. Matching Type

In the following questions more than one option of column I and II maybe

correlated.

(i) is c

(ii) is b

(iii) is d

(iv) is a,e