4. • Alkali metals are most reactive
metals and thus the do not occur
in free state
• They mostly occur as halides,
borates, silicates, nitrates and
oxides
• Some alkali metals occur
abundantly in nature
• Sodium is seventh and potassium
is eight abundant element by
weight in earth’s crust
5. All the alkali metals have
one valence electron ns1
outside the noble gas core.
The loosely held s-electron
in the outermost valence
shell of these elements
makes them the most
electropositive metals. They
readily lose electron to form
monovalent ions. This is the
reason why they are never
found in free state in nature.
6. The alkali metal atoms have
the largest sizes in a particular
period of the periodic table.
With increase in atomic
number, the atomic and ionic
radii of alkali metals increase
on moving down the group,
i.e. from Li to Cs.
7. The ionization enthalpies of
the alkali metals are
considerably low and
decrease down the group
from Li to Cs. Hydration
enthalpies decrease with
increase in ionic sizes.
Li+> Na+ > K+ > Rb+ > Cs+
8.
9. (i) Reactivity towards air
(ii) Reactivity towards water
(iii)Reactivity towards
dihydrogen
(iv)Reactivity towards
halogens
(v) Reducing nature
(vi)Solutions in liquid
ammonia
10. (i) Reactivity towards air: The
alkali metals tarnish in dry air
due to the formation of their
oxides which in turn reacts
with moisture to form
hydroxides. They burn
vigorously in oxygen forming
oxides.
a. 4Li + O2
2Li2O (oxide)
b. 2Na + O2
Na2O2
(peroxide)
c. M + O2
MO2 (superoxide)
(ii) Reactivity towards water: The
alkali metal reacts with water
to form hydroxide and
dihydrogen.
2M + 2H2O 2M+ +2OH- + H2
(M= an alkali metal)
11. (iii) Reactivity towards dihydrogen:
The alkali metals react with
dihydrogen at about 673K (lithium
at 1073K) to form hydrides. All the
alkali metal hydrides are ionic
solids with high melting points.
2M + H2
2M+H-
(iv)Reactivity towards halogens: The
alkali metals readily react
vigorously with halogens to form
ionic halides, M+X-. The Li+ ion is
very small in size and has high
tendency to distort electron cloud
around the negative halide ion.
Since anion with large size can be
easily distorted among halides
lithium iodide is the most covalent
in nature.
12. (v)Reducing nature: The alkali
metals are strong reducing
agents, lithium being the
most and sodium the least
powerful. The standard
electrode potential which
measures the reducing
power represents the overall
change:
M(s) M(g)
sublimation enthalpy
M(g) M+(g) + e-ionization
enthalpy
M+(g) + H2O M+(aq)
hydration enthalpy
13. (vi) Solutions in liquid ammonia:
The alkali metal dissolves in
liquid ammonia giving deep blue
solutions which are conducting
in nature.
M + (x + y)NH3
[M(NH3)x]+ +
[e(NH3)y]-
The solutions are paramagnetic
and on standing slowly librates
hydrogen resulting in the
formation of amide.
M+
(am) + e- +NH3(l) MNH2(am) +
1/2H2(g)
(where ‘am’ denotes solution in
ammonia.)
14. Lithium is used in making alloys .
Lithium carbonate is used in
making a special kind of glass.
Lithium aluminum hydride is used
as reducing agent in synthetic
chemistry. Along with this Sodium
is used in softening of hard water,
laundry, and cleaning, it is also
used in paints and dyes. Sodium is
also used in paper and textiles
industries and as a reagent in
laboratories.
15. 1. Oxides and Hydroxides:
Under appropriate conditions pure
compounds M2O, M2O2 and MO2
may be prepared on combustion in
excess of air. These oxides are easily
hydrolyzed by water to form
hydroxides.
M2O + H2O 2M+ + 2OH-M2O2
+ 2H2O 2M+ + 2OH- + H2O2
2MO2 + 2H2O 2M+ + 2OH- + H2O2 +
O2
16. 2. Halides:
The alkali metal halides, MX (X =
halogen) are all high melting,
colorless crystalline solids. They
can be prepared by the reaction of
the appropriate oxide, hydroxide or
carbonate with aqueous hydrohalic
acid (HX).
The melting and boiling points
always follow the trend: fluoride >
chloride > bromide > iodide. All
these halides are soluble in water.
17. 3. Salts of Oxo-Acids:
Oxo-acids are those in which the
acidic proton is on a hydroxyl
group with an oxo group attach to
the same atom. They are generally
soluble in water and thermally
stable. Their carbonates and
hydrocarbonates are highly stable
to heat.
