Electron configuration

Electron Configuration

Basic Concepts

• An atom’s electron configuration refers to the arrangement of electrons in an atom’s electron shells or energy levels.
• The number of electrons in an atom is the same as the number of protons. This maintains the overall charge balance of the atom.

Energy Levels

• Electron energy levels, also known as shells or orbits, are the regions around the nucleus where electrons are most likely to be found.
• Each energy level can hold a particular number of electrons: the first energy level can hold up to 2, the second can hold up to 8, and the third can hold up to 8.

Electron Configuration Diagram and Notation

• An electron configuration diagram provides a visual representation of the arrangement of electrons. The nucleus is represented by a dot, and the energy levels are shown as concentric circles around the nucleus.
• Electron configuration notation provides a coded way of writing down the arrangement. For instance, oxygen with 8 electrons would be written as 2.6 — 2 electrons in the first shell and 6 in the second.

The Aufbau Principle and Pauli Exclusion Principle

• The Aufbau principle states that electrons fill the lowest energy levels first. Hence, the first energy level is completely filled before electrons begin to occupy the second level, and so on.
• The Pauli Exclusion Principle states that each orbital within an atom can contain, at most, two electrons, and those two electrons must have opposite spins.

Orbital Types

• Energy levels are further divided into sublevels containing orbitals. Each orbital can hold a maximum of two electrons.
• Four types of orbitals exist: s, p, d, and f. The first energy level only has ‘s’ orbitals, the second level has ‘s’ and ‘p’, the third has ‘s’, ‘p’, and ‘d’, and from the fourth level and upwards, all types of orbitals exist.

Hund’s Rule

• Hund’s rule states that electrons prefer to enter empty orbitals in the same sublevel before sharing orbitals with other electrons. This is due to electrons repelling each other as they carry the same charge.

Valence Electrons

• The outermost electrons are referred to as valence electrons. These electrons are important because they take part in bonding with other atoms.

Shell, Subshells and Orbitals Summary

• In summary, energy levels or shells (represented by principal quantum number n) are divided into subshells (s, p, d, f), which further contain orbitals (a max of 2 electrons). The electron configuration of an atom depicts how electrons are distributed in these shells, subshells and orbitals.