Final answer:
The electron configuration for a calcium cation (Ca²⁺) is [Ar], which indicates that it has lost its two outermost electrons and now has the same electronic structure as the noble gas argon, making it isoelectronic with Ar and giving it a 2+ charge.
Step-by-step explanation:
The electron configuration of the calcium cation (Ca²⁺) is determined by removing two valence electrons from the neutral calcium atom's configuration. A neutral calcium atom has the electron configuration of [Ar]4s², which means it has 20 electrons.
When forming a Ca²⁺ cation, it loses these two 4s electrons, resulting in the loss of the entire 4s² subshell. Consequently, the electron configuration for the Ca²⁺ ion becomes [Ar], which signifies that its electronic structure is now the same as that of argon, with 18 electrons. This reflects the general rule that main group elements, when forming cations, tend to lose their valence electrons and adopt the electronic structure of the preceding noble gas.
The Ca²⁺ ion is thus isoelectronic with argon, having a 2+ charge due to the removal of two negatively charged electrons.