How many valence electrons are in an atom of chlorine?

The electron configuration of chlorine is #1s^2 2s^2 2p^6 3s^2 3p^5# or #"[Ne]"3s^2 3p^5#.

The #3s^2 3p^5# electrons are the outermost electrons, so chlorine has seven valence electrons.

In a picture, the valence electrons are the ones in the outermost shell.

You can see in the diagram below that there are seven electrons in the outermost circle.

Additionally, a more basic way of determining the number of valence electrons would be to simply look at what group Cl is in.

It is in Group 17, which means it has 7 valence electrons.

Chlorine has seven valence electrons.

Chlorine has atomic number 17.

The atomic number is the number of protons present in the nucleus of an atom.All the atoms of an element have same atomic number.

In every stable atom the number of electrons is equal to the number of protons. Stable means that atom has not formed a ion yet.

Therefore, the number of electrons is equal to the number of protons in an chlorine atom.

This means, that the number of electrons present in an chlorine atom is 17.

The energy shells of an atom are in the order K, L, M …

So the electronic configuration of chlorine atom is: K, L, M = 2, 8, 7

Valence electrons are the number of electrons present in the outermost shell of an atom.

The last shell of a chlorine atom has 7 electrons in it.

Therefore, there are 7 valence electrons in an chlorine atom.

Here is a video which gives a quick discussion of how to determine how many valence electrons atoms of different elements have.

Video from: Noel Pauller