Electron Configuration Calculator

An electron configuration describes how an atom's electrons occupy shells, subshells, and orbitals. The atomic number gives the proton count and, for a neutral atom, also gives the number of electrons that must be placed. Orbital notation provides a compact map of that arrangement. A term such as 2p4 identifies the second shell, the p subshell, and four electrons occupying that subshell. This calculator follows the Aufbau or building-up order. It fills lower-energy orbitals before higher-energy orbitals using the common sequence 1s, 2s, 2p, 3s, 3p, 4s, 3d, and onward. An s subshell holds two electrons, p holds six, d holds ten, and f holds fourteen. The capacities follow from the number of orbitals in each subshell and the Pauli exclusion principle, which allows at most two electrons with opposite spins in one orbital. Electron configurations help explain the periodic table. Elements in the same group often have similar valence-shell patterns and therefore similar chemical behavior. Alkali metals end with one outer s electron, while noble gases generally have filled outer s and p subshells. Transition metals fill d orbitals, and lanthanides and actinides involve f orbitals. Reading the final occupied subshell can therefore connect an atomic number with bonding, common oxidation states, magnetism, and spectroscopy. The generated notation is the standard Aufbau prediction for a neutral isolated atom. A small set of transition metals has experimentally observed ground-state exceptions because half-filled or fully filled d subshells can be especially stable. Chromium and copper are familiar examples. Ions also require an additional step: add electrons for negative charge or remove them for positive charge, normally removing electrons from the highest principal shell before inner d electrons. Use the result as a dependable learning aid for shell filling and periodic trends. For advanced spectroscopy or a transition-metal exception, compare the predicted string with an authoritative periodic table. The calculator intentionally keeps ordinary numeric exponents on one line so the sequence is easy to copy into homework, notes, laboratory records, or another chemistry application.