1s2, 2s2, 2p6, 3s1
The Aufbau principle states that electrons fill orbitals in order of increasing energy levels. Orbital diagrams visually represent the arrangement of electrons in an atom's orbitals. By following the Aufbau principle and using orbital diagrams, we can understand how electrons are distributed in an atom's electronic configuration.
Bohr &Stoner suggested aufbau principle
4f orbital
The Aufbau Principle is also known as the build-up principle because it describes the process of filling electrons into atomic orbitals starting with the lowest energy orbitals and moving towards higher energy levels. This gradual filling up of electron orbitals reflects the building up of an atom's electronic configuration.
The arrangement of an atom's electrons is known as the atom's electronic configuration. It describes how the electrons are distributed in the atom's orbitals according to the Aufbau principle, Pauli exclusion principle, and Hund's rule.
Each electron occupies the lowest energy orbital. Orbitals related to energy level are of equal energy.
Aufbau
If you are referring to the Aufbau Principle, than I believe it was the Danish physicist Niels Bohr who discovered it around 1920. However, instead of being named after a person, it came from the German phrase Aufbauprinzip which literally translates to "building-up principle."
The electronic configuration od Cu is [Ar] 3d10 4s1 This is an exception to the aufbau principle which would predict [Ar] 3d9 4s2.
It is valid
The correct order in which atomic orbitals are filled according to the Aufbau principle is: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p.
The electronic configuration of bromine (atomic number 35) is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5. This means that it has 35 electrons arranged in energy levels and sublevels according to the Aufbau principle.