1.

Explain the anomalous behaviour of oxygen.

Answer»

Solution :Oxygen is the first element of group 16.
Reasons for anomalous behaviour of oxygen:
(i) It has small size.
(ii) It has high electronegativity (3.5).
(iii) It does not have vacant d-orbitals like other ELEMENTS in group 16.
Oxygen shows following anomalous behaviour :
(i) PHYSICAL state : Oxygen is a gas while other elenments in the group are solids at ordinary temperature.
(ii) Atomicity : Oxygen exists as a diatomic molecule `O_(2)`, while other elements are polyatomic molecules like `S_(8), Se_(8)`, and bu puckered ring structure.
(iii) Magnetic behaviour: (Oct. '14) Molecular oxygen `O_(2)` is paramagnetic while other elements are diamagmetic. Molecular `O_(2)` hastwo unpairedelectrons in theantibondding molecularorbital.
(iv)Oxidation states : (Oct. '14) Oxygen shows oxidation state-2 in oxides, - 1 in peroxides while +2 in oxygen difluoride, `OF_(2)`. Since it does not have vacant d-orbital it doesn't show higher oxidation states while other elements of group 16 show +2, +4 and +6 oxidation states.
(V)Hydrogen BONDING : Since oxygen has high electronegativity (3.5), it FORMS hydrogen bonding in its compounds like H,0, alcohols, etc.
Other elements in the group do not show this property.
(vi) Hydrides : (Oct. '14) The hydride of oxygen, `H_(2),O_(2)`. is a liquid while the hydrides of all other elements in group 16 are gases.


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