Title 3A.S BLOCK ELEMENTS FINAL PHANI SIR-1.pdf ✅

NISHITH Multimedia India (Pvt.) Ltd., 6 3 JEE A JEE MAINS - CW - VOL - I DVANCED - VOL - III S- BLOCK ELEMENTS NISHITH Multimedia India (Pvt.) Ltd., S-BLOCK ELEMENTS Colour of compounds: Compounds of Group 1 metals are typically white, except those where the anion is coloured, for example sodium chromate Na CrO 2 4 (yellow), potassium dichromate K Cr O 2 2 7 (orange), and potassium permanganate KMnO4 (deep purple). In these cases the colour comes from the anions 2 CrO , 4  2 Cr O2 7  or MnO4  and not from the Group 1 metal ions. Reaction with water(Group 1 metals):  Group 1 metals all react with water, liberating H2 and forming the hydroxides.  The reaction becomes increasingly violent on descending the group.  2 2 2Li 2H O 2LiOH H    2 2 2Na 2H O 2NaOH H    2 2 2K 2H O 2KOH H     0 Li / Li E 3.05V    , 0 Na / Na E 2.71V    0 K / K E 2.93V    , 0 Rb / Rb E 2.92V    0 Cs / Cs E 2.92V     Standard electrode potentials 0 E and Gibbs free energy G are related by the equation 0    G nFE where n is the number of electrons removed from the metal to produce the ion, and F = 96500 (Faraday constant)  The reaction Li e Li     has the largest negative 0 E value, and hence the largest positive G value. Thus the reaction does not occur. However, the reverse reaction Li Li e    has a large negative value of G, so lithium liberates more energy than the other metals when it reacts with water. But lithium reacts gently with water ‘ The explanation lies in the kinetics(that is the rate at which the reaction proceeds). Potassium has a low melting point, and the heat of reaction is sufficient to make it melt, or even vaporize. The molten metal spreads out, and exposes a larger surface to the water, so it reacts even faster, gets even hotter and catches fire’. Oxo salts : (carbonates, bicarbonates, nitrates and nitrites):  Group 1 metals are highly electropositive and thus form very strong bases, and have quite stable oxosalts.  Because Group 1 metals are so strongly basic, they also form solid bicarbonates(except LiHCO3 )(LiHCO3 can exist in solution).  No other metals form solid bicarbonates, though NH HCO 4 3 also exists as a solid.  The crystal structures of NaHCO3 and KHCO3 both show hydrogen bonding, but are different.  In NaHCO3 , the HCO3  ions are linked into an infinite chain, whilst in KHCO3 a dimeric anion is formed. C O O H O C O O H O 2  SYNOPSIS