P-block elements -Comparative study of properties of different groups 15-18 of p-block

P-block elements-

 ·       Those elements in which last electron goes in p-orbital are known as p-block elements.

 ·       Consists of elements of group 13-18 of the periodic table 

·       Their valence shell electronic configuration is ns²np^1-6 (except helium 1s²) 

Comparative study of properties of different groups 15-18 of p-block 

s.  no	properties	Gr-15	Gr-16	Gr-17	Gr-18
A	Atomic   properties
1	Elements	N P As Sb Bi	O S Se Te Po	F Cl Br I At	He Ne Ar Kr Xe Rn
2	General valence shell Electronic configuration	ns2np3	ns2np4	ns2np5	ns2np6
3	Atomic size/  Ionic size- Increases down the group (because of increasing in No. Of shell or shelding effect ) while decreases in a period with increase in nuclear charge	Increases down the group   There is considerable increase in covalent radii from N to P but from As to Bi only small increase observed  Due to least shielding effect of completely filled d/f orbital	Increases down the group	Increases down the group	Increases down the group
4	Ionization enthalpy	Decreases down the group with increase size	Decreases down the group with increase size	Decreases down the group with increase size	Decreases down the group with increase size
5	Electron gain enthalpy	Decreases down the group with increase size	Decreases down the group with increase size   Exception - O has less (-)ve than S(because small size and high electron density in oxygen   From S to Po again less negative	Decreases down the group with increase size  Exception-F has less (-)ve   electron gain enthalpy than Cl	No. Tendency to get electron  So, have positive EGE
B	Physical properties
1	Metallic character	Increase on moving down  N,P-Non-Metal  As,Sb –Metalloid  Bi- Typical metal	Increase on moving down  O,S- Non metal  Se, Te-Metalloid  Po-metal	Increase on moving down  F, Cl-gas  Br- liquid  I-solid	Increase on moving down
2	MP/BP	MP first increases from N to As   due to increase in atomic size and then decreases to Sb and Bi due to increase in tendency to form three covalent bonds instead of five covalent bonds with increase in size because of inert pair effect  While BP regularly increases	Increase down the group   Exception  Large difference in mp/bp of O and S since O is diatomic while S is polyatomic Po has lower bp/mp than Te  Due to weak Vander Waals force because of max inert pair effect in Po.	Increases	increases
3	density	increases	increases	increases	increases
4	allotropy	Except N and Bi , all show	All show	no	No.
C	Chemical property
1	Oxidation state	Show –3 +3 +5  -The stability of –3 O.S decrease down the group with increase metallic character  -The stability of +5 O.S decrease down the group due to inert pair effect  -The stability of +3 O.S increase down the group Due to inert pair effect  -Nitrogen shows +1 to +4 Oxidation state  So, it shows disproportionation rex (an element exists in reduced as well as oxidized  3HNO2 ------> HNO2 +2NO + H20	O show   -2      -1(H2O2)    +2(OF2)   Other +2,+4,+6  - The stability of +6 O.S decrease down the group due to inert pair effect  -The stability of +4 O.S increase down the group Due to inert pair effect	All exhibit      –1 o.s Cl Br I show +1, +3, +5 ,   +7	Only Xe and Kr form compound only
2	hydride	EH3	H2E	HE	no
a	Stability α bond dissociation enthalpy	Decreases down in the group  With decrease in bond dissociation enthalpy	Decreases down in the group	Decreases down in the group	-----
b	Reducing nature α 1/E –H bond dissociation	Increases down in group  With decrease in bond dissociation enthalpy	Except H2O all are reducing agent  Increases down in group	Increases down in group	----
c	Basicity α availability of lone pair	Behave as Lewis base  Basic nature Decreases down in the group  (Electron density per unit volume)	Decreases down in the group	Decreases down in the group	-------
d	Acidic character   α   1/E-H bond dissociation enthalpy	Increases down in group            1.Bond angle  Decreases down in group  NH3> AsH3> SbH3> BiH3  With decrease in electronegativity  2.bp decrease from N to P then increase up to Bi   Bp of NH3 > Bp of PH3 since NH3 associated with hydrogen bond while interparticle force in PH3 is Vander Waals force. Its strength increases up to Bi with size, therefore bp increase again from as to Bi	Increases down in group   -due to increase in size of atoms, the distance between central atom and hydrogen increases on moving down ward in a group which favours the release of hydrogen as proton (it is the reason of week bond)  -H2S is gas while H2O liquids due to presence of hydrogen bond in H2O i.e water molecules associated with hydrogen bond  bond angle decreases down in group in various hydride of this group	Increases down in group	-------
3	Oxides	Form two type of oxides E2O3, E2O5  Oxide of N and P-acidic  As and Sb – amphoteric  BiO3-basic predominantly	EO2, EO3	Forms but most of them unstable  F forms OF2, O2F2  Cl, Br,I form oxide containing range of oxidation state of halogen from +1 to +7 o.s  --Mainly covalent bond due to small difference  --->stability of oxide of halogen decreases in the order –I >Cl>Br    Due to polarity in oxide of iodine, pi-bond in Cl and O but these both not present in oxide of bromine

 Difference between Inert Pair Effect and Shielding Effect 

s.no	Inert Pair Effect	Shielding Effect
1	the reluctance of s-electrons pairs of the valence shell to participate in chemical bonding  ns2 electrons are not able to participate because of strong hold of nucleus due to high penetration effect of s electrons or poor shielding effect of inner orbitals   (since completely filled orbitals as (n-1) d10 (n-2) f14 are more dispersed)	In multi electronic atoms the outermost electrons are shielded or screened from the nucleus by the inner electron.  as a result of this, outermost electron does not feel the full nuclear charge, this effect is called screening effect
2	It helps to explain the stability of lower oxidation states for heavier elements of a group.	The shielding effect explains why electrons from the valence shell can be removed easily and size of atom on moving in a group increases