Humber Admissions Practice Test

What does the principal quantum number indicate?

1. The shape of the orbital

2. The energy level occupied by the electron

3. The spin of the electron

4. The type of sublevel

The correct answer is: The energy level occupied by the electron

The principal quantum number is a key concept in quantum mechanics that describes the energy level of an electron in an atom. It is denoted by the symbol \( n \) and takes on positive integer values (1, 2, 3, etc.). The principal quantum number essentially indicates the distance of the electron from the nucleus of the atom, with higher values of \( n \) corresponding to electrons that are further away, and thus have more energy. When \( n \) increases, not only does the average distance of the electron from the nucleus increase, but also the energy associated with that electron increases. This is crucial for understanding the arrangement of electrons in an atom and how they interact with each other and with external energy sources, such as light. Understanding this relationship informs us about the electron's behavior and the overall electron configuration of an atom, which is foundational for concepts in chemistry, such as bonding and reactivity.