Question

What element has the atom whose `K,L,` and `M` shells and `4s` subshell are filled completely and `4p` subshell is half-filled?

Answer 1

The order of filing is
`K,L,M` shells, then `4s^(2),3d^(10)` then `4p^(3)`. The electronic configuration of the element will
`1s^(2)2s^(2)2p^(6)4s^(2)3d^(10)2p^(3)`
(There must be three `4p` electrons)
The number of electron is `Ƶ=33` and the element is As (The `3d` subshell must be filled before `4p` fills up.)