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Valence electrons

The valence electrons of an atom are the electrons found in its outermost electron shell. These are the electrons that can be used to form chemical bonds.

The first electron shell holds up to two electrons while the second shell holds a maximum of eight electrons.

Atoms usually form bonds to obtain a full valence electron shell (or a noble gas electron configuration).

Helium (He), neon (Ne) and argon (Ar) are noble gases. They are elements with complete electron valence shells (i.e. the outermost shells).
Helium (He), neon (Ne) and argon (Ar) are noble gases. They are elements with complete electron valence shells (i.e. the outermost shells).

A complete valence electron shell holds eight electrons, unless the first electron shell is the valence shell. In this case only two electrons are required for a complete shell.

Helium ($$\ce{He}$$) is a noble gas that only has one electron shell. Its valence shell contains two electrons. Neon ($$\ce{Ne}$$) has two electron shells and its valence shell contains eight electrons.