4f orbital
After the 3p orbital, the next atomic orbital is the 4s orbital. In the order of filling according to the Aufbau principle, the 4s orbital is filled before the 3d orbital. Following the 4s, the 3d orbitals are filled, and then the 4p orbitals come next.
An example of a situation where an orbital diagram violates the aufbau principle is in the case of chromium (Cr) and copper (Cu). For chromium, one electron is placed in the 4s orbital instead of the 3d orbital to achieve a more stable half-filled or fully filled d subshell. Similarly, for copper, one electron is placed in the 4s orbital before filling the 3d orbital to achieve a more stable fully filled d subshell.
Chromium is the exception to the aufbau principle. Instead of filling its 4s orbital before the 3d orbitals, one electron goes into the 3d orbital first. This anomaly is due to the more stable half-filled or fully-filled d subshell configuration in the 3d orbitals for chromium ions.
The Aufbau principle states that electrons must be added to elements and ions in a VERY specific order with the lowest energy level being filled first and the highest last. This is where the Aufbau triangle comes in. It shows the order in which the energy levels must be filled.
Each electron occupies the lowest energy orbital. Orbitals related to energy level are of equal energy.
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.
In the electron configuration of an atom, the 4s orbital is generally filled before the 3d orbital due to the lower energy level of the 4s orbital. This follows the Aufbau principle, where electrons fill orbitals in order of increasing energy. Thus, in the electron configuration of an atom, the 4s orbital is filled before the 3d orbital, leading to the configuration 4s2 instead of 3d2.
The 4s orbital falls in a slightly lower energy level than the 3d orbital when it is empty so it will fill with electrons first, but when it is full of electrons it rises to be above the 3d one so that it will lose electrons first as well.
The orbital filling diagram of boron (atomic number 5) shows its electron configuration as 1s² 2s² 2p¹. In the diagram, the 1s orbital is filled with two electrons, the 2s orbital also holds two electrons, and the 2p orbital contains one electron. This results in a total of five electrons distributed across the orbitals, following the Aufbau principle, Pauli exclusion principle, and Hund's rule.
Exceptions to the aufbau principle occur due to the repulsion between electrons in the same orbital. This can cause certain elements to have lower energy by placing an electron in a higher energy orbital. Additionally, electron-electron interactions and exchange energy play a role in determining the actual electron configurations of some elements.
According to the Aufbau principle, atomic orbitals are filled in the following order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, and finally 7p. This order is determined by increasing energy levels, with some overlap between orbitals of different principal quantum numbers. The sequence reflects the relative energy of the orbitals, leading to the Aufbau filling order.
The 5s orbital has a lower energy level than the 4d or 4f orbitals in a rubidium atom, according to the aufbau principle. Electrons fill orbitals starting from the lowest energy level to the highest energy level. This is why the electron fills the 5s orbital before the 4d or 4f orbitals in a rubidium atom.