Question

There are only 8 elements in the third period even the capacity of third shell is 18.Give reason

Answer 1

The y axis shows energy (distance from nucleus) than and the different colours are the electrons in different shells. The green ones are in the third shell while the yellow ones are in the fourth shell. As it shows the fourth shell has two electrons in a slightly lower energy level than some 10 electrons in the third shell. 

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