Question

The principal quantum number of an atom represents:
A.Size of the orbit
B.Spin angular momentum
C.Orbital angular momentum
D.Space orientation of the orbital

Answer 1

We must understand the concept of writing electron configuration of atoms and accordingly find the use of principal quantum number in this aspect. Electronic configuration is the distribution of electrons of the atom of an element into various shells and subshells. Knowing the atomic number tells us the number of electrons which are to be distributed among the orbitals. There are a set of rules which are to be followed before writing the electronic configuration of an atom.

Complete answer:
There exists a set of rules and understandings which must be followed while writing electronic configuration of atoms. The first and the foremost concept is that of principal quantum numbers. Electron in an atom is characterized by a set of four quantum numbers and the maximum number of electrons that can be accommodated in a shell (energy level) is based on principal quantum number (n). The maximum number of electrons that can be accommodated in a shell is calculated by the formula $2{n^2}$ where $'n'$ is the shell number. When n=1, the maximum number of electrons that can be accommodated are $2 \times {\left( 1 \right)^2} = 2$ . The relative total energy of each orbital is represented by the principal quantum number. Each orbital energy level grows as its distance from the nucleus increases. An electron shell is a collection of orbitals that all have the same $'n'$ value.

Hence the correct option is option (A).

Note:
Note that electrons of an atom is characterized by a set of four quantum numbers called principal quantum number “n” and the maximum number of electrons that can be accommodated in a shell is calculated by the formula $2{n^2}$ where $'n'$ is the shell number. If two electrons are filled in the ‘s’ subshell of the first shell, the electronic configuration is noted as $1{s^2}$. Also, Pauli’s exclusion principle states “no two electrons in the same atom have the same values for all four quantum numbers”.