electronconfiguration

Electron configuration describes the arrangement of electrons within an atom's electron shells and subshells. It follows specific rules, including the Aufbau principle, Hund's rule, and the Pauli exclusion principle. The Aufbau principle states that electrons fill orbitals starting from the lowest energy levels and moving upwards. Hund's rule dictates that within a subshell, electrons will occupy each orbital individually before pairing up. The Pauli exclusion principle explains that no two electrons in an atom can have the same four quantum numbers, meaning an orbital can hold at most two electrons with opposite spins.

Electron configurations are typically written using a shorthand notation. For example, hydrogen (H) has one electron, so its configuration is 1s¹. Helium (He) has two electrons, filling the 1s subshell, giving it a configuration of 1s². Lithium (Li) has three electrons; the first two fill the 1s subshell (1s²), and the third enters the next lowest energy level, the 2s subshell, resulting in 1s²2s¹. This notation clearly indicates the principal energy level, the subshell (s, p, d, or f), and the number of electrons in that subshell. Understanding electron configuration is crucial for predicting an element's chemical properties and its position in the periodic table.