Question

When Na and Li placed in dry air we get:
A. $NaOH,{\text{ }}N{a_2}O,{\text{ }}L{i_2}O$
B. $N{a_2}C{O_3},N{a_2}{O_2},L{i_2}O$
C. $N{a_2}O,L{i_3}N,N{H_3}$
D. $N{a_2}O,L{i_2}O,L{i_3}N$

Answer 1

Alkali metals are the highly reactive elements and have a strong tendency to lose an electron from their outermost shell to attain the stable noble gas configuration. They can form stable oxides, halides and sulphides. The alkali metals when reacting with dry air get tarnish due to the formation of oxides.

Complete step by step answer:
1. Alkali metals have low ionization enthalpy, large size and low heat of atomisation that are responsible for the high reactivity of these metals and this reactivity increases down the group.
2. Alkali metals burn very fast in oxygen and tarnish in dry air because of the formation of oxides and when these oxides react with moisture they form hydroxides.
3. They burn very fast in oxygen and form monoxides, peroxides and superoxides.
4. Lithium results in the formation of monoxides, sodium results in the peroxides formation and other metals of the group form the superoxides.
5. The oxidation state is $+ 1$ in all compounds formed by alkali metals with oxygen.
6. Due to the diagonal relationship with magnesium, Lithium forms its nitride $L{i_3}N$ whereas the rest of the alkali metals do not behave in the same manner.
7. The reactions involved in the formation of oxides and peroxides and nitrides are as follows:
$4Li + {O_2} \to 2L{i_2}O$
$2Na + Dry{\text{ }}air({O_2}) \to N{a_2}O + N{a_2}{O_2}$
$6Li + {N_2} \to 2L{i_3}N$
8. When peroxides reacts with water, it forms sodium hydroxide
$N{a_2}{O_2} + 2{H_2}O \to 2NaOH + {H_2}{O_2}$
9. $N{a_2}C{O_3}$ is formed when Sodium hydrogen carbonate is formed using ammonia, carbon dioxide and water and after its formation, the crystals are separated and subjected to heating which results in the formation of sodium carbonate.

**Therefore, the correct answer is option (D).

Note: **
Some applications and facts:
1. Lithium is different from other members of the group due to its exceptionally small size and high charge to mass ratio. It is least reactive among others but it is the strongest reducing agent.
2. Sodium carbonate is used in softening the hard water and used in making glassware, soaps, etc and it is an important lab reagent which can be used both in quantitative and qualitative analysis. Sodium chloride is the common salt and sodium hydroxide is used in making paper, artificial silk etc.