Other exceptions to the Aufbau Principle occur with elements such as molybdenum (Mo), silver (Ag), and gold (Au). These configurations are anomalous, as one electron from the 4s orbital moves to the 3d orbital, leading to half-filled and fully-filled 3d orbitals. Chromium's electronic configuration is 3d^5 4s^1, and copper's electronic configuration is 3d^10 4s^1. Chromium (Cr) and Copper (Cu)Ĭhromium and copper are two elements that deviate from the Aufbau Principle. It states that the orbital with the lowest energy level will be filled first before those with high energy levels. The term comes from the German word 'aufbau', which means 'built up' or 'construction'. The Aufbau rule simply gives the order of electrons filling in the orbital of an atom in its ground state. These exceptions occur when the energy difference between orbitals is small, and it is more energetically favorable for electrons to fill a higher energy orbital than to follow the Aufbau sequence. The Aufbau principle, simply put, means electrons are added to orbitals as protons are added to an atom. Exceptions to the Aufbau PrincipleĪlthough the Aufbau Principle provides a general guideline for the filling of atomic orbitals, there are some exceptions to the rule. Elements are arranged in the periodic table based on their electronic configurations, with elements in the same group having similar configurations. The Aufbau Principle forms the basis for the organization of the periodic table of elements. The knowledge of the electronic configuration of atoms, obtained using the Aufbau Principle, is critical in interpreting electronic spectroscopy data.

Electronic SpectroscopyĮlectronic spectroscopy is a technique used to study the electronic properties of atoms and molecules.

The Aufbau Principle helps in predicting the types of chemical bonds that atoms form based on their electronic configurations.

The knowledge of the electronic configuration of atoms is important in understanding chemical bonding.

Aufbau principle order