What is the electron configuration of Calcium?

The electron configuration of Calcium, which has an atomic number of 20, indicates how the electrons are distributed in its atomic orbitals. In the case of Calcium, the correct configuration reflects that it has 20 electrons. The noble gas preceding Calcium is Argon, which has an atomic number of 18 and provides a stable electron configuration to build upon.

Following Argon, Calcium will have two additional electrons, which will fill the 4s orbital. The resulting configuration is expressed as [Ar] 4s². This notation means that Calcium has the same electron configuration as Argon plus two additional electrons in the 4s subshell.

This configuration aligns with how electrons fill orbitals according to the Aufbau principle, noting that the 4s subshell is filled before the 3d subshell due to its lower energy level in the sequence of orbital filling. Hence, the final electron configuration for Calcium is accurately and succinctly represented as [Ar] 4s².