Electron orbitals overlap because the wave nature of electrons allows them to occupy regions of space simultaneously, even if they are in different energy levels. Electron orbitals are regions where there is a high probability of finding an electron, and they describe the three-dimensional distribution of electron density around an atomic nucleus.
When orbitals from different energy levels overlap, it does not mean that electrons are directly jumping between energy levels without any energy exchange. Instead, the overlap of orbitals facilitates interactions between electrons, leading to the formation of chemical bonds and the sharing or transfer of electrons.
In the context of molecular orbitals, when atoms come together to form molecules, their atomic orbitals combine to give rise to molecular orbitals. The combination of atomic orbitals results in the formation of bonding molecular orbitals and antibonding molecular orbitals. Bonding molecular orbitals have lower energy than the original atomic orbitals, promoting stability and the sharing of electrons between atoms.
For example, in the case of overlapping 2p and 2s orbitals, they can combine to form sigma (σ) bonds in molecules. The electron density is concentrated along the internuclear axis, effectively connecting the nuclei of the participating atoms. This overlapping and sharing of electrons contribute to the formation of stable chemical bonds.
It's important to note that electrons still need energy to move between different energy levels, and such transitions involve the absorption or emission of photons. The overlapping of orbitals does not violate the principle of energy conservation but rather enables the formation of stable molecular structures through the sharing or transfer of electrons.