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Tuesday, 21 February 2017

The P-Block Elements - I


The p-Block elements:

Elements belonging to groups 13 to 18 of the periodic table are called p-block elements.

General electronic configuration of p-block elements:


The p-block elements are characterized by the nsnp1-6 valence shell electronic configuration.

Representative elements:

Elements belonging to the s and p-blocks in the periodic table are called the representative elements or main group elements.

Inert pair effect:

The tendency of ns electron pair to participate in bond formation decreases with the increase in atomic size. Within a group the higher oxidation state becomes less stable with respect to the lower oxidation state as the atomic number increases. This trend is called ‘inert pair effect’. In other words, the energy required to unpair the electrons is more than energy released in the formation of two additional bonds.

GROUP 15 ELEMENTS

Nitrogen family:

The elements of group 15 – nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb) and bismuth (Bi) belong to configuration is ns np3.

Atomic and ionic radii:   
  • Covalent and ionic radii increase down the group.
  • There is appreciable increase in covalent radii from N to P.
  • There is small increase from As to Bi due to presence of completely filled d or f orbitals in heavy elements.
Ionisation energy:
  • It goes on decreasing down the group due to increase in atomic size.
  • Group 15 elements have higher ionisation energy than group 14 elements due to smaller size of group 15 elements.
  • Group 15 elements have higher ionization energy than group 16 elements because they have stable electronic configuration i.e., half-filled p-orbitals.
Allotropy:

All elements of Group 15 except nitrogen show allotropy.

Catenation:

  • Nitrogen shows catenation to some extent due to triple bond but phosphorus shows catenation to maximum extent.
  • The tendency to show catenation decreases down the group.
Oxidation states:
  • The common oxidation states are +3, +5 and –3.
  • The tendency to show –3 oxidation state decreases down the group because of decrease in electronegativity by the increase in atomic size.
  • The stability of +5 oxidation state decreases whereas stability of +3 oxidation state increases due to inert pair effect.
  • Nitrogen shows oxidation states from –3 to +5.
  • Nitrogen and phosphorus with oxidation states from +1 to +4 undergo oxidation as well as reduction in acidic medium. This process is called disproportionation.
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