The d shell is filled before the s shell due to the Aufbau principle, which states that electrons fill orbitals in order of increasing energy. The d orbitals have a slightly higher energy than the s orbitals, so they are filled first.
Yes, the order in which shells are filled follows the Aufbau principle and the Pauli exclusion principle. The Aufbau principle states that electrons fill orbitals in order of increasing energy, while the Pauli exclusion principle states that no two electrons can have the same set of four quantum numbers, thus leading to the specific order of filling.
Yes, the order of filling shells can vary in different atoms due to the different energy levels of the orbitals. For example, in transition metals, the d shell may be filled before the s shell due to the energy levels of the orbitals.
The filling of shells plays a significant role in determining the properties of an element. The number and arrangement of electrons in the shells determine the element's reactivity, chemical bonding, and physical properties such as melting and boiling points.
Yes, there are a few exceptions to the order of filling shells, such as the anomalous electron configuration of chromium and copper. In these cases, a half-filled or completely filled d orbital is more stable, so an electron from the s orbital is promoted to the d orbital. However, these exceptions do not change the overall trend of filling shells in order of increasing energy.