First slide
Chemical properties

D,A,L and Q are 16th group elements of Modern periodic table. The correct trend of volatality of their hydrides is H2D > H2A > H2L > H2Q. The element ‘A’ in the sequence is


Down the group as the size of the atom increases affinity of hydrogen towards central atom decreases. Therefore

a) X-H bond enthalpy decreases….O-H>S-H>Se-H>Te-H;

b) Thermal stability decreases….H2O>H2S>H2Se>H2Te;

H2O and H2S are exothermic products, remaining three hydrides are endothermic products.

c) Reducing power increases…..H2O<H2S<H2Se<H2Te;

d) Acidic strength (Ka) increases…..H2O<H2S<H2Se<H2Te;

e) pKa decreases…..H2O>H2S>H2Se>H2Te;

Down the group as vanderwaal's forces increases

Melting and boiling points increases

Expected BP and MP….H2O<H2S<H2Se<H2Te

Due to H-bonding in H2O, it has higher BP and MP than expected.

BP trend…...H2S<H2Se<H2Te<H2O

MP trend….H2S<H2Se<H2Te<H2O

Central atom in these hydrides contain two lone pairs, according to Bent rules

As the Electronegativity of central atom decreases,

Bond angle decreases…..H2O>H2S>H2Se>H2Te;

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