Pick any of the 118 elements to see its full and noble-gas-shorthand electron configuration, plus an orbital box diagram showing how electrons fill each subshell — one per orbital first (Hund's rule), then pairing.
Noble-gas notation
[Ar]4s2 3d6
Full configuration
1s2 2s2 2p6 3s2 3p6 4s2 3d6
n=1
1s
↑↓
n=2
2s
↑↓
2p
↑↓↑↓↑↓
n=3
3s
↑↓
3p
↑↓↑↓↑↓
3d
↑↓↑↑↑↑
n=4
4s
↑↓
Why some elements look "wrong"
A few elements — chromium and copper are the classic examples — don't follow the simple aufbau pattern you'd predict from filling order alone. Chromium is [Ar]4s1 3d5, not 4s2 3d4, because a half-filled d-subshell is unusually stable. These aren't approximations or errors: they're the real, experimentally measured configurations, and this tool shows them exactly as measured rather than the "expected" pattern.