The element calcium (atomic number 20) has the electron configuration. 1s2 2s2 2p6 3s2 3p6 4s2. or in noble gas form : [Ar] 4s2. The element calcium (atomic number 20) has the electron configuration <br /> 1s2 2s2 2p6 3s2 3p6 4s2<br /><br /> or in noble gas form : [Ar] 4s2.