Each of the noble gases, in the last column of the periodic table, has its last electron shell completely filled. The elements with a filled shell configuration are the most stable and have the lowest tendency of all elements to gain electrons, lose electrons, or share electrons in chemical bonds.
Ionization EnergyThe ionization energy the the amount of energy required to remove an electron from an atom. The highest energy electron is the first one to be removed. Ionization energy is one measure of the stability of an atom. Filled shell electronic configurations are most stable. When one type of orbital (s, p, or d) is either filled or half filled, the atom is more stable than atoms with other partially filled s, p, or d orbitals.
Because they have stable, filled shell configurations, it is difficult to remove an electron from any of the noble gases. The chart below shows ionization energy through the periodic table. Each peak is one of the noble gases. Note that ionization energy decreases from top to bottom of each column because the outer shell electrons become farther removed from the nucleus.
Neon, Argon, KryptonNeon, argon, and krypton are present in the sun and other stars.
Argon is the only inert gas with a significant concentration in the atmosphere (0.9 % of all atmospheric gas molecules) but the others are present in very small quantities.
These elements produce light when an electric discharge passes through the gas. Click here to see a simulation of a neon light.
Why? Think of our discussion of the hydrogen atomic emission spectrum. The energy from the electric discharge causes an electron to be excited to another energy level. Neon, with its filled n=2 shell, has an electron excited to the n=3 or n=4 shell. When the electron falls back down to the ground state, it gives up its extra energy as a photon of visible light.