Humber Admissions Practice Test 2025 - Free Practice Questions and Study Guide for Humber College Admissions

In the context of atomic structure, shells refer to energy levels where electrons are found. These energy levels are integral to understanding how electrons are arranged around the nucleus of an atom. Each shell corresponds to a specific energy state, with the electrons occupying these shells depending on their energy.

Electrons in different shells have distinct energy levels, with those in shells closer to the nucleus generally having lower energy compared to those in outer shells. The concept of shells helps explain various chemical properties and behaviors of elements, including their bonding and reactivity, as the outermost shell (valence shell) is particularly vital for electron interactions.

The other options, while related to atomic structure, do not accurately define shells. Physical orbits around the nucleus suggest a circular path, which is an outdated view in quantum mechanics. Layers of the atom may refer to different concepts in atomic structure but do not specifically capture the notion of shells. Lastly, types of particles in the nucleus pertains to protons and neutrons, which are not described as shells but rather as constituents of atomic nuclei.