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Alkali Metals; Group -1 Elements
y The group 1 elements have ns1 electronic
configuration and are highly reactive metals.
Atomic Electronic
Elements Symbols
Number Configuration
Lithium Li 3 [He]2s1
Sodium Na 11 [Ne]3s1
Potassium K 19 [Ar]4s1
Rubidium Rb 37 [Kr]5s1
Caesium Cs 55 [Xe]6s1
Francium Fr 87 [Rn]7s1
Physical Properties of Alkali Metals :
1. Atomic Size
Largest in their respective period (except
noble gas element) Concept Ladder
Size increases from Li to Cs due to addition
of an extra shell Francium occurs only in
Li < Na < K < Rb < Cs trances as a radioactive
Cs > Rb > K > Ba > Sr > Ca > Na > Mg > Li > Be decay product because its
Comparision of atomic size of Group 1 and 2 half life period is very small
(half-life 21 minutes).
, 2. Oxidation State
The group 1 elements exhibit +1 oxidation Rack your Brain
state
3. Ionization Energy Why second ionization enthalpy
y The value of first ionization energies for the values of alkali metals are very
atoms in this group are lower than those for high?
any other group in the whole periodic table.
(Li > Na > K > Rb > Cs)
y Second ionization energy of alkali metals is
very high because by loosing one electron
they achieve inert gas configuration. Concept Ladder
y Li > Na > K > Rb > Cs (Ionization energy)
4. Density
Alkali metals have largest
Alkali metals have large size which accounts
size and lowest ionization
for their low density
Atomic Mass (M) energies in their respective
Density =
Atomic Volume (V) periods.
Atomic mass increases from Li to Cs in the
group and volume also increases but increase
in atomic weight is more than increase in
volume. Therefore density increases from Li
to Cs.
Li < K < Na < Rb < Cs
Rack your Brain
5. Melting and Boiling point
M.P. and B.P. of alkali metals are low due to
weak interatomic bonds because of their large Why density of K is less than Na?
atomic radii and presence of only 1 valence
electron. (Li > Na > K > Rb > Cs)
6. Electropositive Character
1
Electropositivity ∝
Ionization Energy
Alkali metals have the tendency to lose the
electron.
Concept Ladder
M(g ) → M(g
+
) + e
–
7. Conductivity
Densities of alkali metals
Due to the presence of loosely held valence
increase from Li to Cs
electrons which are free to move in a metal
s-Block Elements
Exception : K is lighter
structure, these elements are good conductor
than Na.
of heat and electricity.
2.
,8. Nature of Bonds
The electronegativity values being low, they Concept Ladder
combine with other elements to form ionic
Alkali metals are soft with
bond.
low melting and boiling
9. Flame Test points. This is due to weak
First group elements and their salts gives metallic bond.
characteristic color to Bunsen flame. By
flame energy electron of outer most shell get
excited, which on returning back to its ground
state releases absorbed flame energy as a
visible light.
The energy released is min. in the case of Li+
and increases in order Li+, Na+, K+, Rb+, Cs+. Concept Ladder
Elements Colour Solution of alkali metals
in liquid ammonia is highly
Li Crimson red conductive and deep blue
in colour. This is due to
Na Golden Yellow
presence of ammoniated
K Violet electrons.
Rb Red Violet
Cs Blue
s-Block Elements
3.
, 10. Electronegativity
The tendency to attract elements is low as Concept Ladder
the alkali metals are electropositive. The
electronetativity, thus decreases from Li to Hydrated radii are in the
Cs as the electropositive character increases. order :
Li+(aq) > Na+(aq) > K+(aq) > Rb+(aq)
11. Specific Heat > Cs+(aq)
The specific heat values decrease from Li to Ionic mobility :
Cs. Li+(aq) < Na+(aq) < K+(aq) < Rb+(aq)
< Cs+(aq)
12. Heat of Atomisation
Heat of atomisation decreases from Li to Cs.
13. Hydration of Ions
The ions are heavily hydrated. The smaller
the size of the ion, the greater is the degree
of hydration. Thus the degree of hydration
decreases down the group from Li+ to Cs+.
Thus with the increase in hydration electrical
Rack your Brain
conductivity decreases.
14. Lattice Energy Why, LiHCO3 exists in solution?
Salts of alkali metals are ionic solids. Lattice
energy of salts of alkali metals having common
anion decreases on descending down the
group.
15. Photoelectric Effect
K, Rb and Cs have quite large atomic size, so
their ionization energy is very low.
Due to very low ionization energy their valence Previous Year’s Questions
shell electrons gets excited even by absorbing
visible light.
The sequence of ionic mobility in
That’s why Cs is used in photoelectric cells.
aqueous solution is
[AIPMT-2008]
16. Reducing Character
(1) Rb+ > K+ > Cs+ > Na+
Alkali metals are strong reducing agents.
(2) Na+ > K+ > Rb+ > Cs+
Reducing character increases down the group.
(3) K+ > Na+ > Rb+ > Cs+
s-Block Elements
(4) Cs+ > Rb+ > K+ > Na+
4.
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