S-Block Elements
Physical Properties of Alkali Metals:
➖These are soft in nature and can be cut with the help of a knife except the lithium.
➖The atoms of alkali metals have the largest size in their respective periods.
➖The first ionization energy of the alkali metals is the lowest as compared to the elements in the other group.
➖The alkali metals show a +1 oxidation state.
➖The alkali metals have low values of reduction potential (as shown in table-I) and therefore have a strong tendency to lose electrons and act as good reducing agents.
➖The melting and boiling points of alkali metals are very low because the intermetallic bonds in them are quite weak.
Hydroxides of Alkali Metals:
a) All the alkali metals, their oxides, peroxides, and superoxides readily dissolve in water to produce corresponding hydroxides which are strong alkalies.
➖2Na + 2H2O → 2NaOH + H2
➖Na2O + 2H2O 2NaOH
➖Na2O2 + 2H2O → 2NaOH + H2O2
➖2KO2 + 2H2O → 2KOH + H2O2 + O2
b) The basic strength of these hydroxides increases as we move down the group Li to Cs.
c) All these hydroxides are highly soluble in water and thermally stable except lithium hydroxide.
d) Alkali metals hydroxides being strongly basic react with all acids forming salts.
➖NaOH + HCI → NacI + H2O
➖2NaOH + H2 SO4 → Na2SO4 + 2H2O
Halides of Alkali metals:
➖M2O + 2HX → 2MX + H2O
➖MOH + HX → MX + H2O
➖M2CO3 + 2HX → 2MX + CO2 + H2O (M = Li, Na, K, Rb or Cs)
(X = F, Cl, Br or I)
➖ll the alkali metals form ionic (electrovalent) compounds.
➖The alkali metals are good conductors of heat and electricity.
➖Alkali metals (except Li) exhibit the photoelectric effect
➖The alkali metals and their salts impart a characteristic color to a flame.
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