Electron Configuration
Write the electron configuration for each element. Use caret notation (e.g., 1s^2 2s^2 2p^6) or superscripts.
Common Questions
What is electron configuration?
Electron configuration describes how electrons are arranged in an atom's orbitals. It follows the aufbau principle (fill lowest energy first), Pauli exclusion principle (max 2 electrons per orbital), and Hund's rule (fill degenerate orbitals singly first).
What is the aufbau filling order?
Electrons fill orbitals in order of increasing energy: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p. A diagonal rule diagram helps remember this order.
What is noble gas core notation?
Noble gas core notation shortens the configuration by replacing the inner electrons with the symbol of the preceding noble gas in brackets. For example, sodium: [Ne] 3s1 instead of 1s2 2s2 2p6 3s1.
What are the exceptions to expected electron configurations?
Chromium is [Ar] 3d5 4s1 (not 3d4 4s2) and copper is [Ar] 3d10 4s1 (not 3d9 4s2). Half-filled and fully filled d subshells have extra stability, so one electron moves from 4s to 3d.