Group 15—The Nitrogen Group
nitrogen
N
electron
configuration
[He]2s22p3
phosphorus
P
[Ne]3s23p3
arsenic
antimony
As
Sb
[Ar]3d104s2 4p3
[Kr]4d105s2 5p3
bismuth
Bi
[Xe]4f14 5d106s2 6p3
symbol
The elements of group 15 are less metallic.
However on going down the group,
the metallic character increases from N to Bi.
Oxidation states
In genera,l elements of group 15 exhibit +3 and +5
oxidation states.
e.g.
phosphorus forms pentahalides
such as PF5, PCl5 (+5 oxidation state)
trihalides PCl3, PF3 (+3 oxidation state).
The stability of +5 oxidation state decreases whereas
stability of +3 oxidation state increases due to
inert pair effect.
Allotropy
Except nitrogen and bismuth, all other elements of
this group show allotropy.
e.g.
Phosphorus exists as - white, black or red
phosphorus
Arsenic exists as - yellow or grey arsenic
Antimony exists as - yellow or silvery grey
allotropic forms.
White phosphorus
Tetrahedral P4 molecule
Red phosphorus
Oxides
Phosphorous forms the following oxides.
+3
+5
P4O6 P4O10
Phosphorus Oxides and Oxyacids
1. Phosphoric acid series - Oxidation state of P is (+5)
2. Phosphorous acid series – Oxidation state of P is (+3)
Phosphoric acid series
e.g.
Orthophosphoric acid (H3PO4)
Polyphosphates
formed from tetrahedral PO4 (phosphate) structural
units linked together by sharing oxygen atoms.
Pyrophosphoric acids
H4P2O7
Tripolyphosphoric acid
H5P3O10
Metaphosphates
The structure of a metaphosphate ion can be
described as being made up of PO4 structural
units in which each unit shares two corners
with another unit.
e. g.
cyclic trimetaphosphate
2. Phosphorous acid series
e.g.
Phosphorous acid (H3PO3)
Hydrides
The elements of groups 15 form trihydrides of the
general formula MH3 such as
Pyramidal structure
Bond angle of the hydrides
Down the group the bond angle decreases as:
Halides
MX3, MX5
Pyramidal
Trigonal bipyramidal (TBP)