The noble gas notation for the electron configuration of calcium (Ca) is [Ar] 4s2. This notation starts with the nearest noble gas that precedes calcium in the periodic table. In this case, argon (Ar) is the noble gas that comes before calcium.
Calcium has an atomic number of 20, which means it has 20 electrons. The electron configuration can be broken down as follows:
- 1s2
- 2s2 2p6
- 3s2 3p6
- 4s2
The configuration can be simplified using the noble gas notation, which uses the configuration of argon to represent the first 18 electrons. Thus, after accounting for argon, calcium has just two additional electrons in the 4s subshell, leading to the final notation of [Ar] 4s2.