Electron Configuration Calculator
Calculate electron configuration with our free science calculator. Uses standard scientific formulas with unit conversions and explanations.
Reviewed by Manoj Kumar, Mathematics Educator
Formula
Fill orbitals: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p... (aufbau order)
Electrons fill orbitals in order of increasing energy following the aufbau principle. Each s orbital holds 2 electrons, each p subshell holds 6, each d subshell holds 10, and each f subshell holds 14. The total electrons equal the atomic number minus the ion charge.
Worked Examples
Example 1: Electron Configuration of Iron (Fe)
Problem:Determine the electron configuration of iron (Z=26).
Solution:26 electrons to place.\n1s2 2s2 2p6 3s2 3p6 4s2 3d6\nShorthand: [Ar] 3d6 4s2\nValence electrons: 2 (in 4s shell)\nIron is a transition metal with partially filled d orbitals.
Result:[Ar] 3d6 4s2
Example 2: Electron Configuration of Cl- Ion
Problem:Find the electron configuration of chloride ion Cl- (Z=17, charge=-1).
Solution:Cl has 17 protons; Cl- has 18 electrons (gained 1).\n1s2 2s2 2p6 3s2 3p6\nThis is the same as argon (noble gas configuration).\nShorthand: [Ne] 3s2 3p6 or simply [Ar]
Result:1s2 2s2 2p6 3s2 3p6
Frequently Asked Questions
What is electron configuration and why is it important?
Electron configuration describes how electrons are distributed among the orbitals of an atom. It follows the aufbau principle (fill lowest energy first), the Pauli exclusion principle (max 2 electrons per orbital with opposite spins), and Hund rule (fill degenerate orbitals singly first). Understanding electron configuration is essential for predicting chemical behavior, bonding patterns, magnetic properties, and the position of elements in the periodic table.
How does electron configuration change for ions?
When an atom forms a cation (positive ion), electrons are removed starting from the outermost shell with the highest principal quantum number. For transition metals, 4s electrons are removed before 3d electrons. For example, Fe is [Ar] 3d6 4s2, but Fe2+ is [Ar] 3d6. When forming anions (negative ions), electrons are added to the lowest available orbital. For instance, Cl gains one electron to become Cl- with the configuration [Ar], achieving a noble gas configuration.
How does electron configuration explain the periodic table's shape and element colors?
The periodic table's block structure (s-block, p-block, d-block, f-block) directly mirrors which subshell is being filled — the two leftmost columns are the s-block, the six rightmost are the p-block, the ten transition-metal columns are the d-block, and the lanthanides/actinides are the f-block. This is also why transition metals are often colorful in solution: partially filled d-orbitals allow electrons to absorb specific visible-light wavelengths during d-to-d electron transitions, which is the electron-configuration basis for the color of compounds like copper sulfate (blue) or potassium permanganate (purple).
References
Reviewed by Manoj Kumar, Mathematics Educator · Editorial policy