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Grade: 12


Explain the physical properties namely Ionisation Energy(I.E) & electropositive or metallic character ,Standard Oxidation Potential Reducing Properties.

11 years ago

Answers : (1)

shashank Saxena
13 Points


Ionisation energy & electropositive or metallic character :

(a)    Due to unpaired lone electron in ns sub-shell as well as due to their larger size, the outermost electron is far from the nucleus, the removal of electron is easier and these have low values of ionization energy (I.E.)
(b)   Ionisation energy of these metals decreases from Li to Cs.

    Ionisation energy        Li         Na      K        Rb       Cs      Fr
    IE1 (kJ mol–1)            520      495    418     403    376     –
    IE2 (kJ mol–1)            7296   4563  3069   2650  2420  –

(c)    Lower is the ionization energy greater is the tendency to lose ns1 electron and to change in M+ ion. Therefore these have stronger electropositive character.
(d)    Electropositive character increase from Li to Cs.
(e)    Due to their strong electropositive character, they emit electrons even when exposed to light showing photoelectric effect. This property is responsible for the use of Cs and K in photoelectric cells.

 Standard Oxidation Potential and Reducting Properties :

(a)    Since alkali metals easily lose ns1 electron and thus they have high values of oxidation potential

(b)    The standard oxidation potentials of alkali metals are listed below :

                                        Li           Na        K            Rb        Cs
    EoOP (in volts)    +3.05       +2.71   +2.93     +2.99   +2.99

    More is oxidation potential, more is the tendency to get oxidized and thus more powerful is reducing nature in aqueous medium. That is why alkali metals liberate H2 from H2O and HCI.

    However, an examination of ionization energy for alkali metals reveals that Li should have the minimum tendency to lose electron and thus its reducing nature should be minimum. The greatest reducing nature of Li in aq. Medium is accounted due to the maximum hydration energy of Li+ ion.

11 years ago
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