Question

hi friends in the above picture you can see some elements and their electronic configuration in M shell it accommodate 18 electrons but in some elements for eg:- potassium its electronic configuration is 2,8,8,1
see M shell it can accommodate 18 electrons know then we can write 2,8,9 know but why is it written as 2,8,8,1 can u explain by doubt

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Answer 1

The electronic configuration of potassium is 2,8,8,1 and not 2,8,9 because an atom can have only 8 electrons in its valence or last shell. ... This actually happens because the k,l,m,n.... shells are again divided into some orbitals s,p,d,f.... . This orbitals have a capacity according to which the electrons in k,l,m,n.

likewise the remaining must be followed

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Answer 2

Answer:

Explanation:

This is because of the existence of various quantum numbers. Potassium's configuration is 1s2 2s2 2p6 3s2 3p6 4s1. The valence electron is present in the 4s orbital, because the previous energy levels are filled with 2 and 6 electrons respectively.

The number electrons in each of the orbitals corresponding to the principal quantum number of potassium is:

1- 2 electrons

2- 2+6= 8 electrons

3- 2+6= 8 electrons

4- 1 electron

Therefore, the configuration is simplified to 2,8,8,1.

Now if it was 2,8,9, it would mean the orbitals under principal quantum number 3 have 9 electrons, which would mean a possible d orbital for potassium because 3s and 3p orbitals together can accomodate only 8.

But due to the aufbau principle, it is not possible to have a 3d orbital without having a 4s orbital. But filling up the 4s orbital adds the electrons to principal quantum number 4.

In the case from scandium through zinc, the 4s orbital is full and 3d orbitals start to fill. Now the principal quantum number is 3 again so the 21st electron in scandium just adds up to the 3s and 3p orbital electrons.