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As described above, burning of alkali metals in air produces oxide, peroxide and super-oxide depending upon the alkali metal. (Li forms oxide, Na forms peroxide and higher alkalis form super-oxide).

However, all the five alkali metals can be made to form the above three types of oxides by dissolving the metal in liquid ammonia and bubbling in the appropriate amount of oxygen.

All monoxides are basic, form hydroxides when treated with water.

The peroxides contain the [—O—O—]2- ion. They are diamagnetic (no unpaired electrons) and are oxidizing agent.
They form hydrogen peroxide on reacting with water
Na2O2 + 2H2O 2NaOH + H2O2

The super-oxides contain the ion [O2]- and are paramagnetic due to the presence of one unpaired electron. These are stronger oxidizing agent than peroxides. On reacting with water, both H2O2 and O2 are released.
KO2 + 2H2O KOH + H2O2 +O2


The hydroxides of alkali metals are the strongest bases known in aqueous solution. The strength of the hydroxide increases from LiOH to CsOH.
Explanation: As the size of cation increases, its influence on the associated anion decreases. Their inter-nuclear separation increases in crystal lattice resulting in the easy removal of hydroxide ions.
The solubility of alkali hydroxides in water increases on descending the group, LiOH is much less soluble.
Alcoholic KOH is used in organic chemistry because its solubility in alcohol is more than that of NaOH. The solubility is due to the reaction
C2H5OH + OH-C2H5O- + H2O

Thermal stability of hydroxides also increases on descending the group. This is due to decreasing perturbing effect of alkali metal ion on hydroxide ion because of increase in size of metal ion.

Reaction with Halogens

Alkali metals react with halogens to form the ionic halides.
2M  +   X2    2MX
(alkali)   (halogen)
The following trends are observed for the variation of melting points:
  1. Melting points of alkali metal halides decrease in the order
    MF > MCl > MBr > MI
    The Figure shows the variation of melting points for sodium halides.
  2. Melting points of lithium halides are less than those of sodium halides and later they generally decrease when we move to cesium halides, with one or two exceptions.

The Figure below shows the variations of melting points for alkali chlorides. The exceptionally low melting point of lithium chloride is due to its covalent character.



The covalent character of LiX (where X = Cl, Br, I) increases as the size of halide increases. This is due to the fact that the smaller sized Li+ions polarizes the larger anion more predominantly. Hence, the extent of covalent character increases as LiCl < LiBr < LiI.

Carbonates and Bicarbonates

Alkali metals are highly electropositive and thus form very strong bases. Alkali carbonates are quite stable. Alkali bicarbonates also exist, no other metals form bicarbonates with the exception of NaHCO3. The solubilities of both carbonates and bicarbonates increase on descending the group



Group 1 nitrates are fairly low melting solids, and are among most stable nitrates known. On strong heating, they decompose into nitrites, and at higher temperatures to the oxide.
2NaNO3 2NaNO2 + O2
4NaNO3 2Na2O + 5O2 + 2N2

Nitrites produce brown fumes of NO2 when treated with dilute acids.
2NaNO2 + 2HCl 2NaCl + H2O + NO2 + NO
2NO + O2 2NO2

Sodium nitrite is manufactured by absorbing oxides of nitrogen in Na2CO3 solution.
Na2CO3 + NO2 + NO 2NaNO2 + CO2

Other methods of preparing nitrites are the reduction of nitrates and reacting of NO with a hydroxide.
KNO3 + Zn KNO2 + ZnO
2KOH + 4NO 2KNO2 + N2O + H2O
4KOH + 6NO 4KNO2 + N2 + 2H2O.


Group 1 metals react with hydrogen, forming ionic or salt-like hydrides. The ease with which they form hydride decreases on descending the group.
With AlCl3, lithium hydride forms lithium aluminum hydride which is a powerful reducing agent.
4LiH + AlCl3 Li[AlH4] + 3LiCl

Reaction with Compounds containing Acidic Hydrogen

Hydrogen gas is released.
2M + C2H5OH 2C2H5OM + H2
2M + 2HC CH 2MC CH + H2.

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