Final answer:
The principal quantum number (n) indicates the energy level of an electron in an atom, which defines the general range of energy for the electron and its probable distance from the nucleus.
Step-by-step explanation:
The principal quantum number, represented by the symbol n, indicates the energy level occupied by an electron within an atom. Electron energy levels are discrete distances from an atom's nucleus, and they are quantized, meaning electrons can only reside at certain energy levels denoted by whole numbers like 1, 2, 3, etc. Electrons at lower energy levels (n=1) are closer to the nucleus, while those at higher levels (n=2, 3, ...) are found further away. The principal quantum number also correlates with the row number of the atom on the periodic table.
Energy levels can be thought of as concentric circles around the nucleus, with the energy increasing as the principal quantum number increases. This quantum number is crucial in determining the general energy range of an electron and its probable distance from the nucleus. However, it does not define the speed, the exact position, or the shape of the electron cloud—other quantum numbers are responsible for those properties.