Electron Configuration Calculator

• What is Electron Configuration?

Electron configuration describes how electrons are arranged in the orbitals and shells of an atom. Think of it as an address system where each electron has a unique location in the atom. This arrangement is not random—it follows fundamental rules of quantum mechanics and directly determines the chemical and physical properties of an element.

💡 Why does this matter? The way electrons are distributed explains why atoms react the way they do, what colors they display, and how strong their bonds are.

• Orbitals and Shells Explained

Electrons occupy different energy levels (numbered 1, 2, 3...) and subshells (labeled s, p, d, f). Each subshell can hold a specific maximum number of electrons:

• Filling Order: The Aufbau Principle

Electrons fill orbitals in order of increasing energy—starting from the lowest energy orbitals first. This is called the Aufbau Principle. The filling order is:

Notice that 4s fills before 3d. This is because 4s orbitals have lower energy than 3d orbitals, even though 4 is numerically larger.

• Hund's Rule: Electron Pairing

When filling orbitals of equal energy, electrons prefer to occupy separate orbitals with parallel spins before pairing up. Why? Because electrons repel each other, so keeping them apart minimizes this repulsion.