How many electron shells can an atom have at maximum?

Atoms can have a maximum of seven electron shells, corresponding to the principal quantum numbers n = 1 through n = 7. These shells determine the energy levels of electrons in an atom. Each shell can hold a specific maximum number of electrons, calculated using the formula 2n², where n is the principal quantum number.

The first shell (n=1) can hold 2 electrons, the second (n=2) can accommodate 8, the third (n=3) can contain 18, the fourth (n=4) can take 32, and so forth, but as the principal quantum number increases up to 7 (the maximum), these shells are associated with larger and more complex electron arrangements.

The seventh shell is reached when n=7; this corresponds with energy levels that can accommodate electrons with higher energy states. It's important to note that although the electron configuration of elements typically fills these shells gradually as you move across the periodic table, seven shells represent the theoretical maximum based on quantum mechanics. This knowledge is foundational in understanding atomic structure and the behavior of elements in various chemical interactions.