First slide
Chemical properties

L,A,Z,D and J are 15th group elements belonging to Modern periodic table. The correct trend of dissociation constant(ka) of hydrides is LH3 > AH3 > ZH3 > DH3 > JH3. The element ‘Z’ 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….N-H>P-H>As-H>Sb-H>Bi-H ;

b) Thermal stability decreases….NH3>PH3>AsH3>SbH3>BiH3 ;

NH3 is exothermic product,remaining four hydrides are endothermic products.

c) Reducing power increases….NH3<PH3<AsH3<SbH3<BiH3 ;

d) Acidic strength (Ka) increases….NH3<PH3<AsH3<SbH3<BiH3 ;

e) pKa decreases……NH3>PH3>AsH3>SbH3>BiH3 ;

Down the group as vanderwaal's forces increases

Melting and boiling points increases

Expected BP and MP….NH3<PH3<AsH3<SbH3<BiH3

Due to H-bonding in NH3, it has higher BP and MP than expected.

BP trend…...PH3<AsH3<.NH3<SbH3<BiH3

MP trend…..PH3<AsH3<.SbH3<BiH3<NH3

Central atom in these hydrides contain one lone pair, according to Bent rules

As the Electronegativity of central atom decreases, 

Bond angle decreases….NH3>PH3>AsH3>SbH3>BiH3 ;

Down the group as the size of central atom increases, electron density on central atom decreases. Thus

a) Basicity decreases,Lewis base strength decreases…..NH3>PH3>AsH3>SbH3>BiH3 ;

b) Electron donating power decreases……NH3>PH3>AsH3>SbH3>BiH3 ;

c) Ligand strength and ability to form dative bond decreases….NH3>PH3>AsH3>SbH3>BiH3 ;

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