What is the total maximum number of electrons that can occupy the third energy level of an atom?

The maximum number of electrons that can occupy an energy level in an atom is determined by the formula 2n², where n is the principal quantum number corresponding to that energy level. For the third energy level, n is equal to 3.

Using the formula:

2(3)² = 2(9) = 18.

Thus, the total maximum number of electrons that can occupy the third energy level is indeed 18. This capacity is rooted in the structure of atomic orbitals as they fill with electrons; the third energy level can have up to four subshells (s, p, d, and f) which collectively can hold 18 electrons. This understanding is crucial for grasping broader concepts in atomic structure, including electron configuration and the behavior of elements in the periodic table.