Position of elements in the Modern Periodic Table:
Elements are placed in groups according to their valence electrons and placed in periods according to the number of shells present in them.
| Position of Elements | |||
|---|---|---|---|
| Valence Electrons | Group | No. of Shell | Period |
| 1 | 1 | 1 | 1 |
| 2 | 2 | 2 | 2 |
| 3 | 13 | 3 | 3 |
| 4 | 14 | 4 | 4 |
| 5 | 15 | 5 | 5 |
| 6 | 16 | 6 | 6 |
| 7 | 17 | 7 | 7 |
| 8 | 18 | ||
Helium has valence electrons equal to 2, but it is placed in group number 18 because it is a noble gas and has completely filled outermost shell.
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