Question

Explain the anomalous behaviour of oxygen in relation to the properties of the Group 16 elements.

Answer 1

Oxygen shows following anomalous behaviour : 

• Physical state : Oxygen is a gas while other elements in the group are solids at ordinary temperature. 
• Atomicity : Oxygen exists as a diatomic molecule O₂ while other elements are polyatomic molecules like S₈, Se₈ have puckered ring structure. 
• Magnetic behaviour : Molecular oxygen O₂ is paramagnetic while other elements are diamagnetic. Molecular O₂ has two unpaired electrons in the antibonding molecular orbitals. 
• Oxidation states : Oxygen shows oxidation state-2 in oxides, – 1 in peroxides while + 2 in oxygen difluoride, OF₂. 
• 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. 
• Hydrogen bonding : Since oxygen has high electronegativity (3.5), it forms hydrogen bonding in its compounds like H O, alcohols, etc. Other elements in the group do not show this property. 
• Hydrides : The hydride of oxygen, H₂O is a liquid while the hydrides of all other elements in group 16 are gases. 
• Covalency : Oxygen shows a common covalency 2 since it has only two unpaired electrons and no d - orbitals in its valence shell. In rare cases, it shows covalency 4. 
• The other members of Group 16 can show covalency, more than 4, due to the presence of J-orbitals in their valence shell.