Orbital Diagram Generator

How to draw an orbital diagram

1. Count the electrons. For a neutral atom this equals the atomic number. Subtract the charge for a positive ion, and add it for a negative ion.
2. Write the electron configuration by filling subshells in order of increasing energy (the Aufbau order below).
3. Draw the boxes. One box for each orbital: 1 box for an s subshell, 3 for p, 5 for d and 7 for f.
4. Add the electrons. Put one up arrow in every box of the subshell first, then go back and add down arrows to pair them up.
5. Check your count. The total number of arrows must equal the number of electrons from step 1.

The three rules behind every orbital diagram

Subshell capacity

Filling order

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p.

This order follows the Madelung rule: subshells fill in order of increasing (n + l), and when two subshells tie, the one with the lower n fills first. For example, 4s (4 + 0) fills before 3d (3 + 2).

Solved examples

Example 1: Oxygen (Z = 8)

Configuration: 1s² 2s² 2p⁴.
1s: [↑↓]   2s: [↑↓]   2p: [↑↓][↑][↑]
The four 2p electrons spread over three boxes by Hund’s rule, so oxygen has 2 unpaired electrons and is paramagnetic.

Example 2: Iron (Z = 26)

Configuration: [Ar] 4s² 3d⁶.
4s: [↑↓]   3d: [↑↓][↑][↑][↑][↑]
Iron has 4 unpaired electrons.

Example 3: Iron(III) ion, Fe³⁺ (24 − 1 = 23 electrons)

The two 4s electrons leave first, then one 3d electron, giving [Ar] 3d⁵.
3d: [↑][↑][↑][↑][↑]
Fe³⁺ has 5 unpaired electrons, the maximum possible for a d subshell, which makes it especially stable.

Why do 4s electrons leave first in transition metal ions?

Although 4s fills before 3d, once the 3d subshell holds electrons it becomes lower in energy than 4s. The 4s electrons are also in the outermost shell, farther from the nucleus. So when a transition metal forms a positive ion, the electrons are removed from the highest shell (highest n) first, and within the same shell from the subshell with the higher l. That is why Fe²⁺ is [Ar] 3d⁶ and not [Ar] 4s² 3d⁴. Negative ions simply gain electrons in the normal Aufbau order.

Common exceptions to the Aufbau order

A few elements do not follow the filling order exactly. A half-filled or completely filled d subshell is slightly more stable, and the energies of nearby subshells are very close, so one electron shifts from s to d. The calculator uses the observed ground states.

Unpaired electrons and magnetism

An orbital diagram shows at a glance how many electrons are unpaired. Atoms or ions with one or more unpaired electrons are paramagnetic and are weakly attracted to a magnetic field. Those with every electron paired are diamagnetic and are weakly repelled.

Frequently asked questions

What is an orbital diagram?

An orbital diagram (also called an orbital box diagram) shows how the electrons of an atom or ion are arranged in individual orbitals. Each orbital is a box, and each electron is an arrow, with up and down arrows showing the two spin directions.

What is the difference between an electron configuration and an orbital diagram?

An electron configuration such as 1s² 2s² 2p⁴ only tells you how many electrons are in each subshell. An orbital diagram also shows how those electrons are spread over the individual orbitals and whether they are paired or unpaired.

What does Hund’s rule mean for the diagram?

In a subshell with more than one orbital, put one electron in each box first, all with the same spin, before pairing any of them. For example, three 2p electrons are drawn as three single up arrows, not as one pair and one single.

How many electrons can each subshell hold?

An s subshell holds 2 electrons, p holds 6, d holds 10 and f holds 14. This comes from 1, 3, 5 and 7 orbitals, each holding a maximum of two electrons.

How do I write the noble-gas shorthand?

Replace the inner electrons with the symbol of the previous noble gas in square brackets, then write the remaining subshells. Iron, for example, is written [Ar] 4s² 3d⁶ instead of 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶.

Should I write 3d before 4s or after?

Both are used. Some textbooks write subshells in filling order (4s before 3d), others group them by shell number (3d before 4s). This calculator uses filling order. Follow the convention your teacher or exam board uses.

Disclaimer: this tool is intended for study and quick checks. Ground-state configurations are taken from the commonly accepted experimental data, and a few heavy elements are still debated. Anions are generated with the standard filling order. For exams, follow your syllabus conventions.