Helium and neon have high ionization energies primarily because of their electron configurations and the nature of their atomic structure.
Ionization energy is the amount of energy required to remove an electron from an atom, resulting in the formation of a positively charged ion. The ionization energy is influenced by two main factors: the effective nuclear charge and the distance between the valence electrons and the nucleus.
Helium has an atomic number of 2, indicating that it has two electrons. Its electron configuration is 1s², which means it has a completely filled 1s orbital. This configuration is highly stable because the 1s orbital can hold only two electrons. As a result, removing an electron from helium requires a significant amount of energy, as it would disrupt the stable configuration.
Neon, with an atomic number of 10, has a similar situation. Its electron configuration is 1s² 2s² 2p⁶, which corresponds to a completely filled valence shell. Like helium, neon also has a highly stable electron configuration. The removal of an electron from the stable outer shell requires a substantial amount of energy.
Additionally, both helium and neon belong to the noble gas group on the periodic table. Noble gases are known for their low reactivity and chemical stability due to their full valence shells. The stable electron configurations of helium and neon make it difficult to remove an electron and form a positive ion.
In summary, helium and neon have high ionization energies because of their stable electron configurations and the difficulty in removing electrons from their filled valence shells.