1. Electron Configuration: When a subshell is completely filled, all the available orbitals within that subshell are occupied by electrons. This results in a stable electron configuration.
2. Exchange Energy: Electrons within the same subshell experience exchange energy, which is an interaction energy that arises from the quantum mechanical exchange of electrons between identical particles. When a subshell is completely filled, the exchange energy becomes maximum. This is because all the electrons in a filled subshell have the same spin orientation, either all up or all down. This maximum exchange energy contributes to a lower overall energy state for the electrons in the filled subshell.
3. Pauli Exclusion Principle: The Pauli Exclusion Principle states that no two electrons can occupy the same quantum state simultaneously. When a subshell is completely filled, it means that all the available quantum states within that subshell are occupied. This restricts the electrons from occupying higher energy states, which results in a lower overall energy configuration.
4. Nuclear Charge and Electron-Electron Repulsion: The energy of electrons in an atom is also influenced by the attraction between the positively charged nucleus and the negatively charged electrons. When a subshell is completely filled, the increased number of electrons in that subshell leads to stronger electron-electron repulsion. This repulsion opposes the attractive force between the electrons and the nucleus, resulting in a slight increase in the energy of the electrons in the filled subshell.
Overall, the complete filling of a subshell leads to a decrease in the energy of the electrons within that subshell due to the maximum exchange energy and the restriction imposed by the Pauli Exclusion Principle. However, there is a slight increase in energy due to increased electron-electron repulsion. The combined effect results in a more stable and lower energy configuration for the electrons in the filled subshell.
