The electron configuration of argon is 1s2 2s2 2p6 3s2 3p6. This means that argon has two electrons in the first energy level, two electrons in the second energy level, and six electrons in the third energy level. The third energy level is also known as the valence shell, and it is the electrons in the valence shell that determine an atom's chemical properties. Argon has a full valence shell, which means that it is very stable and does not readily react with other atoms.