Electronic configuration of selenium

Electrons in each shell

Selenium has 34 electrons arranged as 2, 8, 18, 6 across 4 shells, which is why it sits in period 4.

How to write it

Electrons fill orbitals in order of increasing energy: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p… Each s orbital holds 2 electrons, p holds 6 and d holds 10. Placing Selenium's 34 electrons in that order gives 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁴.

Selenium at a glance

Other elements in group 16

Elements in the same group have the same number of outer electrons, which is why they behave alike.