Build electron configurations by filling orbitals interactively. Shows aufbau principle, orbital diagrams, and quantum numbers.
Placing electrons into orbital boxes lets you compare an orbital diagram with compact subshell notation and quantum numbers. The builder makes the Pauli exclusion principle, Hund's rule, and the usual Aufbau filling sequence visible as the configuration changes. A common mistake is treating the left-to-right position of equivalent p, d, or f orbitals as uniquely physical. That drawing convention can affect an electron's displayed m_l value without changing the subshell occupancy.
A concrete input and expected output from the current implementation.
Input
Fill the 1s orbital with one spin-up electron and one spin-down electron.
Expected output
Electron configuration: 1s^2. Orbital diagram: 1s [up, down]. Quantum numbers of the second electron: n = 1, l = 0, m_l = 0, m_s = -1/2.
The 1s subshell contains one orbital, so both electrons have n = 1, l = 0, and m_l = 0. The specified second electron has the opposite spin required for two electrons sharing an orbital.
Add electrons to individual orbital boxes. Each box accepts at most two electrons, and a pair must have opposite spins. Filled s, p, d, and f subshells therefore contain 2, 6, 10, and 14 electrons because they contain 1, 3, 5, and 7 orbitals respectively. The compact configuration records each subshell's occupancy.
The Aufbau guide presents the usual approximate order for filling subshells. Separate boxes within a subshell make Hund's rule visible. For an electron, n identifies the shell; l identifies s, p, d, or f as 0, 1, 2, or 3; m_l ranges from -l through +l; and m_s is +1/2 or -1/2.
No. The Aufbau sequence is a useful baseline, but several elements have observed ground-state occupancies that differ from its simplest step-by-step prediction. This matters particularly for some d-block and f-block atoms. Use the builder to inspect a proposed arrangement, but compare exception-sensitive configurations with authoritative atomic data.
A diagram must assign equivalent orbitals a left-to-right order. For example, three p boxes can be labeled with m_l values -1, 0, and +1, but their visual order is conventional. Changing that mapping can change the highlighted electron's m_l label while leaving the p-subshell occupancy and compact electron configuration unchanged.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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