Argon (Ar) is a noble gas with an atomic number of 18. As a noble gas, argon has a stable electron configuration and is known for its low reactivity.
The electron configuration of argon is 1s^2 2s^2 2p^6 3s^2 3p^6, representing the filling of the first three energy levels. In terms of valence electrons, argon has eight valence electrons. Valence electrons are the electrons in the outermost energy level (also known as the valence shell), which, in the case of argon, is the third energy level (3s^2 3p^6).
Having a full valence shell of eight electrons contributes to argon's stability and low reactivity. Noble gases like argon typically do not readily gain, lose, or share electrons in chemical reactions because their electron configurations are already highly stable. This stable configuration is often referred to as the "octet rule," as it corresponds to a full valence shell with eight electrons, except for helium, which has only two electrons in its valence shell.
In summary, argon has eight valence electrons, which contributes to its stability as a noble gas and its low reactivity in chemical reactions.