Question

what is principal quantum number?

Answer 1

An atomic orbital is defined by a set of quantum numbers and the first one is principal quantum number.It identifies the shell and thus determines the size and the energy of the orbital.It can have only positive integer values and is symbolised as ‘n’.
n can have values 1,2,3 and so on. Hydrogen and helium atoms have electrons in the first shell and have principal quantum number 1. Lithium has principal quantum number 2 and thus has two shells in its atom.