Question

Lithium forms $L{{i}_{2}}O$ while other alkali metals form peroxides and superoxides because:
A. Ionisation potential of $Li$ is more
B. Hydration energy of $Li$ is more
C. The smaller $L{{i}^{+}}$ ion cannot stabilize the larger peroxide or superoxide ion
D. Both A and B

Answer 1

Hint: Try to recall that lithium shows anomalous behaviour because of its small size and high polarizing power and strong intermetallic bonding. Now, by using this you can easily find the correct option from the given ones.

Complete step by step answer:
- We know that lithium is the first element of group I (alkali metals) and differs from the rest of elements of this group in many aspects contrary to the expectations.
- Lithium also shows a diagonal relationship with magnesium.
- Lithium combines with oxygen to form monoxides while other members of its group form peroxides and superoxides.
- Lithium cannot form peroxide while sodium can cause positive charge is located over a small size of lithium and there is a positive field around it which will attract negative ions so strongly that it does not permit the oxide ion to combine with another oxide ion.
- Hence, lithium forms monoxide while in case of sodium charge is located over a comparatively bigger atom which allows oxide ion to combine with another oxide ion in order to form peroxide ion.
So, the correct answer is “Option C”.

Note: Note that other alkali metals like potassium, caesium, etc. form superoxide ions by the combination of two peroxide ions. Also, you should remember that lithium carbonate on heating decomposes to give carbon dioxide gas while other alkali metal carbonates do not.