How do you calculate number of valence electrons?

1 Answer
Apr 15, 2014

For a main group element, a valence electron is an electron that has the highest principal quantum number, n.

You may tell the number of valence electrons in a main group element by looking at the group number.

Calculation of valence electrons from

For example, bromine atom has 7 valence electrons.

The electron configuration of Br is 1s² 2s²2p⁶ 3s²3p⁶ 4s²3d¹⁰4p⁵.

The electrons with the highest quantum number are the 4s²4p⁵ electrons, and there are 7 of them.

It is easier to refer to the table than to write the electron configuration every time.