The S-block Elements

Li₂CO₃ is a covalent compound whereas Na₂CO₃ is an ionic compound. Therefore, lattice energy of Na₂CO₃ is higher than that of Li₂CO₃. Thus, LiCO₃ is decomposed at a lower temperature as compared to Na₂CO₃.

Potassium carbonate cannot be prepared by Solvay process because potassium hydrogencarbonate is too soluble to be precipitated by the addition of ammonium hydrogencarbonate to a saturated solution of potassium chloride.

Due to small size, the ionization enthalpies of Be and Mg are much higher than those of other alkaline earth metals. Therefore, a large amount of energy is needed to excite their valence electron, and that's why they do not impart colour to the flame.

Different concentrations of alkali metals in liquid ammonia gives different colours. The dilute solutions impart blue colour due to presence of ammoniated electrons whereas the concentrated solutions have copper bronze colour as  ammoniated metal ions are bound by free electrons.

Potassium and caesium have much lower ionization enthalpy than that of lithium. As a result, these metals easily emit electrons on exposure to light. Due to this, K and Cs are used in photoelectric cells rather than lithium.

Alkali and alkaline earth metals are reducing agents. That is why these metals are not obtained by chemical reduction methods.

(i) Ionization enthalpy. Because of high nuclear charge the ionization enthalpy of alkaline earth metals are higher than those of the corresponding alkali metals.

(ii) Basicity of oxides. Basicity of oxides of alkali metals are higher than that of alkaline earth metals.

(iii) Solubility of hydroxides of alkali metals is higher than that of alkaline earth metals. Alkali metals due to lower ionization enthalpy are more electropositive than the corresponding group 2 elements.

It is because ionization enthalpy? H_i of potassium = 419 kJ mol^-1. Ionization enthalpy of sodium = 496 KJ mol^-1. Since Ionization enthalpy of potassium is less than that of sodium, potassium is more reactive than sodium.