Why can a total of 18 electrons can be placed in the 3rd energy level?

Question

Avery Adams · Accepted Answer

The total number of electrons possible in the sublevels of the 3rd energy level is 18.

The third energy level, n=3, contains the 3s, 3p, and 3d sublevels. The maximum number of electrons in the 3s sublevel is two, the maximum number of electrons in the 3p subsevel is six, and the maximum number of electrons in the 3d sublevel is ten. So #2+6+10=8#.

Kai Bowman · Answer

undefined The third energy level, or n=3 shell, consists of one 2s orbital and three 2p orbitals. Each orbital can hold a maximum of 2 electrons, so the total number of electrons that can be accommodated in the 3rd energy level is the sum of the electrons in the 2s and 2p orbitals: 2 (for the 2s orbital) + 2 (for each of the 3 2p orbitals) = 2 + 2(3) = 2 + 6 = 8 electrons. Additionally, according to the aufbau principle, the 3rd energy level can also include the 3s and 3p orbitals, each capable of holding a maximum of 2 electrons. Therefore, the total number of electrons that can be placed in the 3rd energy level is 8 (for the 2s and 2p orbitals) + 2 (for the 3s orbital) + 6 (for the 3p orbitals) = 8 + 2 + 6 = 16. Adding the maximum capacity of the 3rd energy level orbitals gives 8 + 8 = 16 electrons.