# In potassium and calcium,the fillings of electrons in  N-shell starts after M-shell has acquired 8 electrons although M-shell can accomodate upto18 electrons.why?

• First rule: The maximum number of electrons present in a shell is given by the formula 2n2, where ānā is the orbit number or energy level index (1, 2, 3ā¦). Hence, the maximum number of electrons that different shells can accommodate is as follows:

1. First orbit or K-shell can accommodate maximally 2 x 12= 2 electrons.
2. Second orbit or L-shell can accommodate maximally 2 x 2
2= 8 electrons.
3. Third orbit or M-shell can accommodate maximally 2 x 3
2= 18 electrons.
4. Fourth orbit or N-shell can accommodate maximally 2 x 4
2 = 32 electrons.

• Octet rule: The maximum number of electrons that can be accommodated in the outermost orbit is eight.
• Third rule: Electrons cannot be filled in the outer shell until the inner shells are completely filled. This means that shells are filled in a step-wise manner, starting from the inner shell.

So, in potassium and calcium elements, M-shell contains 8 electrons respectively and N shell contains 1 and 2 electrons respectively. because M-shell can aquire maximum 18 electrons but due to octet rule it has only 8 electrons in potassium and calcium. It can have 18 electrons only when N shell contain minimum 1 electron.

Hope this clears to you!

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Bohr and Bury together suggested certain rules to show how electrons are distributed in different orbits.

First rule: The maximum number of electrons present in a shell is given by the formula 2n², where ‘n’ is the orbit number or energy level index (1, 2, 3…). Hence, the maximum number of electrons that different shells can accommodate is as follows:

1. First orbit or K-shell can accommodate maximally 2 x 1² = 2 electrons.
2. Second orbit or L-shell can accommodate maximally 2 x 2² = 8 electrons.
3. Third orbit or M-shell can accommodate maximally 2 x 3² = 18 electrons.
4. Fourth orbit or N-shell can accommodate maximally 2 x 4² = 32 electrons.

Second rule: The maximum number of electrons that can be accommodated in the outermost orbit is eight.

Third rule: Electrons cannot be filled in the outer shell until the inner shells are completely filled. This means that shells are filled in a step-wise manner, starting from the inner shell.

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thanx...

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FOR THIS BEST WAY IS STUDYING SPDF TYPE OF DISTRIBUTION

BUT AS AN ANSWER IN CALCIUM ITS AT NO IS 20 SO THE ARRANGEMENT WOULD BE 2 8 8 2 BECAUSE IT VALENCY WOULD BE 2 AND WHEN IT WILL LOSE 2 ELECTRONS THEN ITS OUTERMOST ORBIT WILL BE COMPLETELY FILLED

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