Question

1.) What is an equation for the maximum number of electrons in a given shell, n?

2.) Write down the electron configurations for: Ni, Rb, As, Na, Si, Br

. Please explain how to read electron configuration after 4s (i.e, where is the mysterious 3d group that comes after 4s? and where do I know when to start counting for 4f?)

Thanks again expert Q&A!

Answer 1

1)  maximum number of electrons in a given shell = 2n²

The number of electrons present in one shell can be calculated by using 2n² formula where n is the no. Of shell like no. 1 shell no. 2 shell etc.

2) Ni = [Ar] 3d⁸ 4s²

Rb = [Kr] 5s¹

As = [Ar] 3d¹⁰ 4s² 4p³

Na = [Ne] 3s¹

Si = [Ne] 3s² 3p²

Br = [Ar] 3d¹⁰ 4s² 4p⁵

4s orbitals have a lower energy than the 3d, and so the 4s orbitals are filled first.The 3d orbitals have a higher energy than the 4s and so for these elements, the 4s levels fill before than the 3d.

Energy of 4s orbital is less than 3d orbital because energy is governed by (n+l) rule.

For 4s ,n=4 and l=0.

For 3d ,n=3 and l=2.

So (n+l) for 4s is less than 3d.

So it has a lower energy than 3d orbital