In H2-like molecules, how do 1s orbitals relate to their energy levels?

In diatomic molecules such as hydrogen (H2), both atoms possess a 1s orbital. When these two 1s orbitals come together, they combine to form molecular orbitals through a process known as linear combination of atomic orbitals (LCAO).

In this scenario, both 1s orbitals are of equal energy and contribute equally to the formation of the molecular orbitals. As a result, they create a bonding molecular orbital that is lower in energy than the individual 1s orbitals since the combination allows for greater electron density between the two nuclei. This leads to a stabilization of the system, which is a critical aspect of bond formation.

When the two 1s orbitals interact, they not only form a bonding molecular orbital but also an anti-bonding molecular orbital. However, it's essential to note that the original 1s orbitals themselves remain at the same energy level prior to any interaction. Thus, their equal energy and interaction create a stable bonding arrangement that effectively lowers the energy of the combined system compared to the individual atomic orbitals alone.