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Question
Explain the following properties of group 16 elements :
1) Electro negativity
2) Melting and boiling points
3) Metallic character
4) Allotropy
Solution
1) Electronegativity :
The elements of group 16 have higher values of electronegativity than the corresponding elements of group 15. Oxygen is the second most electronegative element, the first being fluorin. The electronegativity decreases on going down the group. The decrease in electronegativity down the group is due to increase in size of the atoms.
2) Melting and boiling points :
The melting and boiling points increases with the increase in atomic number as we go down the group.
3) Metallic character :
The first four elements namely oxygen, sulphur, selenium and tellurium are non-metals. The non-metallic character is stronger in O and S are weaker in Se an Te. On the other hand, last element is markedly metallic. However, it is radioactive and is only short-lived.
4) Allotropy :
All the elements of the group exhibit allotropy. For example, oxygen exists as O2 and O3 (ozone.) Sulphur exists in a number of allotropic forms of which yellow ortho-rhombic, α and β -monoclinic forms are most important. All these allotropic forms of sulphur are nonmetallic. Selenium exists in eight allotropic forms of which three are red monoclinic forms containing Se8 rings.
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