Electron Configuration: Find Any Element’s Electrons

An electron configuration shows how an atom’s electrons are distributed among orbitals, making it easier to understand an element’s position and chemical behavior. Enter an element’s atomic number or name to get its ground-state configuration; this calculator uses the Aufbau filling order, with known exceptions for selected atoms.

Formula

This calculator returns the atomic number, Z, as a lookup key for the element’s ground-state electron configuration. The configuration itself is not a numerical formula: it is built by assigning electrons to orbitals in order of increasing energy, subject to the Pauli exclusion principle and Hund’s rule, then checking for established exceptions.

• Z = atomic number, a whole-number count of protons; for a neutral atom it is also the number of electrons.
• Orbital capacities are s: 2, p: 6, d: 10, and f: 14 electrons.

The calculator accepts atomic numbers from 1 through 118. Its output is the number to use when finding the element’s configuration in the steps below; it does not encode an orbital string. An element name or symbol can be used instead of the atomic number by looking up its position in the periodic table.

Worked Example

For the default input, the atomic number is 26.

1. Element 26 is iron (Fe).
2. A neutral iron atom has 26 electrons.
3. Filling orbitals and applying the ground-state arrangement gives 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶.
4. The shorthand form is [Ar] 4s² 3d⁶.

The calculator output is 26, the atomic number used to identify iron and determine its electron count when neutral.

Assumptions

• The target is an isolated, neutral atom in its ground state, not an ion or excited atom.
• The atomic number must be an integer from 1 to 118.
• Configurations use standard orbital notation and noble-gas shorthand where useful; a few atoms have experimentally established arrangements that differ from a simple filling-order prediction.

What You’ll Need

• The element’s name, symbol, or atomic number from a periodic table.
• A periodic table showing atomic numbers and, preferably, a subshell filling diagram.
• A way to count electrons and record the subshell capacities: s², p⁶, d¹⁰, f¹⁴.

Step-by-Step

1. Identify the element and its atomic number. Find the element’s symbol or name in a periodic table. The atomic number is the whole number of protons, usually printed above or near the symbol. Do not use the atomic mass: it is a different quantity. The calculator above accepts the atomic number directly.
2. Decide whether you are writing a neutral atom or an ion. For a neutral atom, electron count equals atomic number. For an ion, adjust the count by its charge: subtract electrons for a positive charge and add electrons for a negative charge. For example, Fe²⁺ has 26 − 2 = 24 electrons. This page’s calculator identifies the element only; it does not adjust for charge.
3. Use the orbital filling order. Fill subshells in this sequence: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p. This is the Aufbau order for the usual ground-state construction. A diagonal-rule chart is a useful way to check the sequence.
4. Respect each subshell’s capacity. Put up to 2 electrons in an s subshell, 6 in p, 10 in d, and 14 in f. Move to the next subshell when the current one is full, except that the last subshell may be partially filled. Write the number of electrons as a superscript. Stop once the total equals the atom’s electron count.
5. Check the electron total. Add the superscripts. For a neutral atom, the sum must equal the atomic number; for an ion, it must equal the adjusted electron count. If the sum is too high, remove electrons from the end of your filling list. If it is too low, continue filling.
6. Apply known ground-state exceptions. A simple filling sequence predicts many elements correctly, but some transition metals have slightly different observed arrangements. Common examples are chromium, [Ar] 4s¹ 3d⁵, and copper, [Ar] 4s¹ 3d¹⁰. For heavier elements, consult a reliable periodic-table reference rather than assuming every arrangement from the diagonal rule.
7. Use noble-gas shorthand if desired. Replace the completed inner-shell configuration with the symbol of the preceding noble gas in square brackets, then write the remaining subshells. For iron, the full form is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶; the shorthand is [Ar] 4s² 3d⁶.
8. For a transition-metal ion, remove electrons from the correct subshell. Although 4s fills before 3d in the basic order, electrons are generally removed from 4s before 3d when a transition metal forms a cation. For example, neutral iron is [Ar] 4s² 3d⁶, while Fe²⁺ is [Ar] 3d⁶. Check the ion’s charge and total again.

Common Mistakes

• Using atomic mass as the electron count. Atomic mass is not the atomic number. Use the proton count; for a neutral atom, that is also the electron count.
• Forgetting the ion charge. A positive ion has fewer electrons than its neutral atom, while a negative ion has more. Keep track of the charge sign.
• Exceeding subshell capacity. The superscript cannot exceed 2 for s, 6 for p, 10 for d, or 14 for f. Recheck the order if a subshell goes over its limit.
• Assuming the filling order is an exception-free rule. Chromium and copper are standard introductory examples where the observed ground state differs from the simplest prediction.
• Removing transition-metal electrons in the wrong order. For common transition-metal cations, remove the outer s electrons before d electrons, even though that s subshell filled earlier.
• Mixing full and shorthand notation. In shorthand, the bracketed noble gas replaces the entire inner configuration. Do not write both the bracket and the same inner subshells again.

Tips

• Use a diagonal filling chart as a memory aid, then verify exceptions separately.
• Write down the target electron total before filling; crossing off electrons as you go helps prevent off-by-one errors.
• Use noble-gas shorthand for long configurations, but keep the full version available when learning or checking the electron count.
• For ions, write the neutral configuration first, then adjust the electron number and apply the appropriate removal or addition rules.
• State whether a configuration represents a neutral ground-state atom or a particular ion. The same element can have multiple electron configurations when charged or excited.

Troubleshooting

The subshells add to the wrong total: confirm the atomic number and charge, then check that each capacity is respected. For a neutral atom, the superscripts must sum to the atomic number.

Your result disagrees with a reference: check whether it shows an ion, an excited state, or a different notation convention. Then check for a known exception, especially among transition metals and heavier elements.

You cannot find a filling chart: use the ordered subshell sequence in Step 3 and capacity limits in Step 4. Keep a running total, and stop at the required number of electrons.

The calculator rejects your input: enter a whole-number atomic number from 1 to 118. If you have an element symbol, look up its atomic number first. This calculator does not take a charge or element name as input.

Frequently Asked Questions

What does an electron configuration tell you?
It shows how an atom’s electrons occupy shells and subshells. This helps describe valence electrons and patterns in chemical behavior.

How do I know how many electrons an element has?
Read its atomic number. A neutral atom has that many electrons; adjust the count for an ion’s charge.

What is the difference between full and noble-gas shorthand?
Full notation lists every occupied subshell. Shorthand replaces the inner electrons’ configuration with the symbol of the preceding noble gas in brackets.

Why does 4s fill before 3d, but lose electrons first?
The filling order is a useful guide for neutral atoms, but relative orbital energies can change as electrons are added or removed. For common transition-metal cations, the outer 4s electrons are removed before 3d electrons.

Do electron configurations apply to ions?
Yes, but you must account for the ion’s charge. Remove electrons for positive ions and add them for negative ions, following the correct orbital rules.

Are electron configurations always unique?
Not across all conditions. An element can have different configurations when ionized or excited; tables usually report the ground state of the neutral atom unless stated otherwise.

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in z | Atomic number | - | 26 | 1 | 118
out e | Electron configuration code | - | z | 0