The outermost shell that has electrons

The idea

The outermost shell of an atom that contains electrons is its valence shell, and the electrons in it are its valence electrons.

The outer edge of the atom

The electrons of an atom sit in shells around the nucleus.

Sodium has the configuration 2, 8, 1. Which electrons are in its outermost shell?

• Just 1 electron
• 8 electrons
• All 11 electrons

Find the valence shell

Change Z. The orange ring is the valence shell and the orange dots are the valence electrons.

Valence shell

The outermost shell that holds electrons is the valence shell. The electrons in it are the valence electrons.

The outermost shell containing electrons is the valence shell, and the electrons in it are the valence electrons.

Notes

The valence shell is the outermost shell that has electrons, and its electrons are the valence electrons.

Check yourself

What is the outermost shell containing electrons called?

Oxygen has the electronic configuration 2, 6. How many valence electrons does it have?

Answer: 6

The outermost shell holds 6 electrons, so oxygen has 6 valence electrons.

Magnesium has the electronic configuration 2, 8, 2. How many valence electrons does it have?

Answer: 2

The outermost shell holds 2 electrons.

Sodium has the configuration 2, 8, 1. Which is its valence shell?

• The K shell. The K shell is the one closest to the nucleus. It is the valence shell only for atoms like hydrogen and helium, whose electrons are all in it.
• The nucleus. The nucleus is the dense centre of the atom, not a shell.
• The valence shell — correct. Yes!
• The M shell, with 1 electron — correct. Yes!
• The K shell, with 2 electrons. The K shell is the innermost shell, not the outermost.
• The L shell, with 8 electrons. The L shell is full but it is not the outermost shell with electrons.