Final answer:
Electrons in an atom are found in specific energy levels called electron shells, each with a unique principal quantum number 'n'. These energy levels are quantized, allowing electrons to jump between levels by absorbing or emitting energy.
Step-by-step explanation:
Electrons move around the nucleus and are only located in specific energy levels called electron shells. These energy levels are akin to the steps of a staircase where electrons can be on one step or another but not in the space between. In an atom, the energy of an electron is described as quantized, meaning electrons can only have specific energy values.
The energy levels are identified by a principal quantum number, denoted as 'n', which indicates the shell number. These shells are arranged as concentric circles around the nucleus, and the electrons within a shell have a probability of being located within that specific region of space. The further away from the nucleus, the higher the value of 'n', and consequently, the higher the energy level.
Electrons can transition between these levels by absorbing or emitting energy, which results in the characteristic atomic spectra. In essence, electrons occupy distinct energy levels within an atom and must absorb or lose the right amount of energy to move between these levels.