Cause Of Periodicity
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Cause Of Periodicity
Periodic Properties of Class 11
According to the Modern Periodic Law, the Properties of the elements are repeated after certain regular intervals when these elements are arranged in order of their increasing atomic number. Therefore the cause of periodicity in properties is the repetition of similar outer electronic configuration at certain regular intervals.
All the elements of group IA i.e. alkali metals have similar outer electronic configuration i.e. ns1, which are given below
| Symbol | Atomic No. | Electronic configuration |
|---|---|---|
| Li | 3 | 1s22s1 or [He]2s1 |
| Na | 11 | 1s22s22p63s1 or [Ne]3s1 |
| K | 19 | 1s22s22p63s23p64s1 or [Ar] 4s1 |
| Rb | 37 | 1s22s22p63s23p63d104s24p65s1 or [Kr] 5s1 |
| Cs | 55 | 1s22s22p63s23p63d104s24d105s25p66s1 or [Xe] 6s1 |
| Fr | 87 | 1s22s22p63s23p63d104s24p64d104f145s25p65d106s26p77s1 or [Rn] 7 s1 |
Thus it is because of similarity in electronic configuration that all the elements have similar properties
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