Electron Configuration Calculator

About Electron Configuration Calculator

Electron configuration shows how electrons fill orbitals. Follow the Aufbau principle: 1s → 2s → 2p → 3s → 3p → 4s → 3d → ...

How to use this calculator

1. Enter the element name, symbol, or atomic number, for example helium, He, or 2.
2. Check the full electron configuration that fills orbitals from lower to higher energy.
3. If the tool gives a shortcut form, compare it to the noble gas in brackets.
4. Use the result to count valence electrons and identify the outer shell.

The formula explained

Electron configuration is written by filling orbitals in order, such as \(1s^2 \, 2s^2 \, 2p^6\). Each part tells you the energy level, sublevel, and how many electrons are in that sublevel.

• s = an orbital sublevel that can hold up to \(2\) electrons
• p = an orbital sublevel that can hold up to \(6\) electrons
• d = an orbital sublevel that can hold up to \(10\) electrons
• f = an orbital sublevel that can hold up to \(14\) electrons
• n = the principal energy level, or shell
• the superscript = the number of electrons in that sublevel

Step by step method

1. Find the atomic number, because it tells you how many electrons a neutral atom has.
2. Fill orbitals in the usual order, starting with \(1s\), then \(2s\), \(2p\), \(3s\), \(3p\), and so on.
3. Place electrons into each sublevel until you use all of them, following the capacity of each sublevel.
4. If needed, rewrite the result with a noble gas shortcut, such as \([Ne]\) or \([Ar]\), for a shorter configuration.

Worked example

Problem. Find the electron configuration for oxygen, \(O\), atomic number \(8\).

1. Oxygen has \(8\) electrons.
2. Fill from the lowest energy upward, so the first \(2\) go into \(1s\), giving \(1s^2\). The next \(2\) go into \(2s\), giving \(2s^2\).
3. The remaining \(4\) electrons go into \(2p\), giving \(2p^4\). The full configuration is \(1s^2 \, 2s^2 \, 2p^4\).

Tips and common mistakes

• Remember that the superscript tells the number of electrons in that sublevel, not the number of the shell.
• For neutral atoms, the total of all superscripts must match the atomic number.

Frequently asked questions