The 4 orbitals filled in the second period are one 2s (with 2 electrons) and three 2p (with 6 electrons).
Electronic configuration in second period
- The second period starts with Lithium and Beryllium which have 3 and 4 electrons and hence the last electrons enter the level 2s and they have an electronic configuration of 1s22s1 and 1s22s2, it is followed by the start of the 2p orbital filling.
- It starts with Boron (1s22s22p1) and ends with Neon (1s22s22p6) which marks the completion of the L shell.
- Thus, 8 elements are present in the second period.