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Boddu rama krishna Best Answer
Electron shells are slightly different Energy levels are described by four quantum numbers. Generally you only need to refer to orbitals using terms like 3p2. (The spin can also be given if required.) The first number is called the principal number, and also called the shell number. For the lighter atoms the shells have large steps in energy and are physically staged apart too. So they literally do form shells. The orbitals start to overlap with heavier atoms, and change in relative energy. However the shell descriptor can still be used to refer to the principal number.