Question

How do you know how many electrons to place in each electron shell/ energy level in different element atoms?

Answer 1

1.You can use some hints,sometimes it can be included in periodic table and
looks like this
1s2 2s2 2p6 3s2 3p6 4s1 it is for K and means that 2
electrons is in first S-level and 2 electrons on second S-level, 6 electrons on
second P-level, 2 electrons in third S-level ,the same with other levels

2, Or you can remember maximum electrons per level. For S-level it is 2,
For P-level it is 6, for D-level it is 10.
Element's number is the number of
electrons and you can fill them one by one on the different levels, using the
knowledge of the maximum of electrons in level