Question

How many orbitals can exist at the third main energy level?

Answer 1

Hint: The third main energy level contains a subshell of one s-orbital, three sets of p-orbital and five sets of d-orbitals. The maximum electron s-orbital can hold is 2, p-orbital is 6 and d-orbital is 10.

Complete step by step answer:
A nucleus is surrounded by a large amount of space which contains electrons. This space is divided into regions called principal energy levels.
Each principal energy level has one sub level which contains one s-orbital. The total electrons present in s-orbital is 2. The electrons present in this orbital are called s electrons and are the lowest in energy as compared to other principal energy levels. The first principal energy level can hold only two electrons and contain one orbital.
Each principal energy level above the first energy level contains one s-orbital and three p-orbital. The maximum electrons present in a p-orbital is 6 electrons. So, the second principal energy level can hold maximum 8 electrons and contain one s-orbital and three p-orbital.
Each principal energy level above the second energy level contains one s-orbital, three p-orbital and five d-orbital. The maximum electrons present in a d-orbital is 10 electrons. So, the third principal energy level can hold maximum 18 electrons and contain one s-orbital, three p-orbital and five d-orbital.
Therefore, the third main energy level contains one s-orbital, three p-orbital and five d-orbital so the total orbitals will be 9.

Note:
Each principal energy level contains $2n^2$ electrons, where n is the number of levels. For, third energy level $2(3{)}^2$= 18 electrons. So, the total electron's third energy level is 18.