How are electrons distributed in atomic orbitals?

Electrons are distributed in atomic orbitals according to the Pauli Exclusion Principle and Hund's Rule.

The distribution of electrons in atomic orbitals is a fundamental concept in chemistry, and it's governed by a set of rules known as quantum mechanics. The two key principles that dictate this distribution are the Pauli Exclusion Principle and Hund's Rule.

The Pauli Exclusion Principle states that no two electrons in an atom can have the same four quantum numbers. Quantum numbers are a set of four numbers that describe the properties and location of an electron in an atom. They include the principal quantum number (n), the azimuthal quantum number (l), the magnetic quantum number (m), and the spin quantum number (s). The principal quantum number defines the energy level of the electron and its distance from the nucleus. The azimuthal quantum number defines the shape of the orbital, while the magnetic quantum number defines the orientation of the orbital in space. The spin quantum number, on the other hand, describes the direction of the electron's spin.

Hund's Rule, on the other hand, states that electrons will fill degenerate (equal energy) orbitals singly before they start to pair up. This is because electrons are negatively charged and repel each other, so they prefer to occupy their own space if possible. This rule is often visualised using an electron filling diagram, where each box represents an orbital and each arrow an electron.

The distribution of electrons in atomic orbitals is also influenced by the Aufbau Principle, which states that electrons fill the lowest energy orbitals first. This principle is often represented by the Aufbau diagram, which shows the order in which orbitals are filled.

In summary, the distribution of electrons in atomic orbitals is a complex process governed by the principles of quantum mechanics. Understanding these principles is crucial for predicting the chemical behaviour of atoms and molecules.