Page 28 - index

Group VA and VIA Elements eLearn.Punjab

Oxygen has two allotropic forms (O2 and O3), sulphur has 3(α, β, γ), Se has
two (red and grey) ,Te has two (metallic and non-metallic). They also show

the property of catenation. This property decreases down the group. All

the elements are polymeric in nature ( they form poiy-atomic molecules).

They attain the electronic configuration of the nearest noble gas by gaining
2 electrons forming O-2, S-2, Se-2, etc. Except oxygen the other members of

the group show a covalency of +2 ,+4, and +6, for example, SCl2, SCl4, SCl6.
+2 oxidation state is shown due to 2 unpaired electrons in the p-orbitals.

+4 oxidation state is shown when 1 electron from p-orbilal is promoted to

the next vacant d-orbital, while + 6 oxidation state is shown when another

electron from s-orbital is also promoted to the next vacant d-orbital.

4.4.2 Occurrence

Oxygen is the most widely distributed and common of all
the elements, comprising about 50% of the earth’s crust.
About one-fourth of the atmospheric air by weight consists of free oxygen
and water contains nearly 89% of combined oxygen. The calcium carbonate
which occurs as chalk, limestone, marble etc, contains 48% oxygen. Silica
which is found in flint, quartz, etc, contains more than 53% oxygen by weight.

Sulphur is also widely distributed in nature both as free and in combined forms.

Many important metallic ores are sulphides, e.g, galena (PbS),

Zinc blende (ZnS), cinnabar (HgS), stibnite (Sb2S3), copper pyrite
(Cu2S.Fe2S3), iron pyrite (FeS2), etc. Some important sulphates are
also found in nature, e.g. gypsum (CaSO4), heavy spar (BaSO4),
etc.

Sulphur also occurs in organic compounds present in animals
and vegetables. Onions, garlic, mustard, hair, many oils, eggs
and proteins consist of compounds containing sulphur in
them . It also occurs as a constituent of coal and petroleum .

4.4.3 Comparison of Oxygen and Sulphur

Smililarities: configuration of

1. Both oxygen and sulphur have same outer electronic
ns2p4.
2. Both oxygen and sulphur are usually divalent.
3. Both oxygen and sulphur exhibit allotropic forms.

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