In a multi-electron atom, several forces or interactions are present that do not occur in a hydrogen atom, which has only one electron. These additional interactions include:
- Electron-electron repulsion: In multi-electron atoms, electrons repel each other due to their negative charges. This mutual repulsion affects the energy and spatial distribution of electrons, complicating the atom's behavior compared to hydrogen, where only one electron interacts with the nucleus
- Shielding (or screening) effect: Inner electrons partially shield outer electrons from the full positive charge of the nucleus. This reduces the effective nuclear charge felt by outer electrons, influencing their energy levels and orbital shapes. Such shielding is absent in hydrogen because there is only one electron
- Energy level splitting within the same principal quantum number (n): Unlike hydrogen, where all orbitals with the same n have the same energy, multi-electron atoms exhibit energy differences among orbitals of the same shell (e.g., 3s, 3p, 3d). This splitting arises due to electron-electron repulsions and shielding effects
- More complex electron-nucleus attraction: Although the nucleus still attracts electrons, in multi-electron atoms this attraction is modulated by the presence of other electrons, leading to contraction of orbitals and changes in energy compared to hydrogen
In summary, the key new interaction in multi-electron atoms is the electron- electron repulsion and the resulting shielding effect , which together cause differences in orbital energies and electron behavior not seen in the single-electron hydrogen atom
