Heisenberg's uncertainty principle (introductory)
Matter waves · Physics
Bohr atom
Interactive 3DElectrons orbit the nucleus in shells — switch element to see H, He and Li fill their shells.
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Study notes
Hydrogen (Z = 1) has one electron in the n = 1 shell. Bohr's model gives its energy levels Eₙ = −13.6/n² eV, so the ground state is −13.6 eV and the first excited state is −3.4 eV. Dropping from n = 2 to n = 1 emits a photon of 10.2 eV — the Lyman-alpha line. Helium (Z = 2) fills the first shell with 2 electrons; lithium (Z = 3) starts the second shell.