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Inorganic Chemistry |
Ionization energy of alkali metals : |
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(i) 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 low values of ionization energy. (I.E.)
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(ii) Ionization energy of these metal decreases from Li to Cs. |
| Ionization energy Li Na K Rb Cs Fr |
IE1 520 495 418 403 376 – |
| IE2 7296 4563 3069 2650 2420 – |
A jump in 2nd ionization energy (huge difference) can be explained as, |
Removal of |
Removal of |
| Li: 1 s2 2s1 —————> Li+ : 1 s2 —————> Li2+ : 1 s1 |
2 selection |
1 selection |
| Removal of 1s electrons from Li+ and that too from completely filled configuration requires much more energy and a jump in 2nd ionization is noticed. |
(iii) Lower are ionization energy values, greater is the tendency to lose ns1 electron to change in M+ ion (i.e. M ® M++e–) and therefore stronger is electropositive character. |
(iv) Electropositive character increases from Li to Cs. |
| 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 cell. |
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