What is called the energy levels around the nucleus of an atom?

The term that refers to the energy levels around the nucleus of an atom is "Principal Energy Levels." These levels are quantized and represent the different energy states that electrons can occupy in an atom. Each principal energy level is associated with a specific energy and is denoted by the principal quantum number (n), which can take values of 1, 2, 3, etc. This provides a foundational understanding of an atom's electronic structure.

While "Shells" is often used synonymously with principal energy levels in informal contexts, it lacks the specificity tied to quantum mechanics. "Orbitals," on the other hand, describe the probable locations of electrons within these energy levels but do not directly refer to the energy levels themselves. Lastly, "Sublevels" refers to the divisions within principal energy levels (such as s, p, d, and f) and provides further detail about the shape and energy of these orbitals. Therefore, "Principal Energy Levels" is the most accurate term to describe the energy levels surrounding an atomic nucleus.