Atomic Structure

Protons, neutrons and electrons, electron configuration, shells and orbital diagram of any element or ion.

Enter the element as a symbol (Fe), a name (iron) or a number (26). The mass number selects an isotope (for example, 37 for chlorine-37); if empty, the rounded atomic mass is used. Ion charge: 2+, 3-, + or -.

Test yourself

The atomic structure calculator takes an element symbol, name or number and finds the numbers of protons, neutrons and electrons, the distribution of electrons by shells, the electron configuration and the orbital diagram of the valence subshells. You can set an isotope (mass number) and an ion charge.

Composition of an atom

p⁺ = Z, n⁰ = A − Z, e⁻ = Z − q

Z is the atomic number, A the mass number, q the ion charge (0 for a neutral atom).

Electron configuration

Subshells fill in order of increasing energy (the Aufbau, or Madelung, rule): 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d… An s subshell holds up to 2 electrons, p up to 6, d up to 10, f up to 14. By Hund's rule electrons first occupy empty orbitals one at a time.

Some elements are exceptions: Cr is 3d⁵4s¹ and Cu is 3d¹⁰4s¹, because a half-filled or filled d subshell is more stable. The calculator takes these exceptions into account.

Example. Fe: p = 26, n = 56 − 26 = 30, e = 26; 1s²2s²2p⁶3s²3p⁶3d⁶4s².