First slide
Chemical properties

D,A,L and Q are 17th group elements of Modern periodic table. The correct trend of thermal stability of their hydrides is HD > HA > HL > HQ. The element ‘D’ 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….HF>HCl>HBr>HI ;

b) Thermal stability decreases…..HF>HCl>HBr>HI ;

c) Reducing power increases…..HF<HCl<HBr<HI ;

d) Acidic strength (Ka) increases…..HF<HCl<HBr<HI ;

e) pKa decreases…..HF>HCl>HBr>HI ;

Down the group as vanderwaal's forces increases

Melting and boiling points increases

Expected BP and MP….HF<HCl<HBr<HI

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

B.P trend…...HCl<HBr<HI<HF

M.P trend….HCl<HBr<HF<HI

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