Question

How do I know how to assign quantum numbers to electrons?

Answer 1

The trajectory and mobility of an electron in an atom can be described using quantum numbers. Quantum numbers are a set of numbers that describe the position and energy of an electron in an atom. Principal, azimuthal, magnetic, and spin quantum numbers are the four types of quantum numbers.

Complete answer:
The main rule is that no two electrons in the same atom can have the same quantum numbers for all four of them.
The four quantum numbers are:
The sign ‘$n$ ' stands for the principal quantum numbers. They stand for the atom's primary electron shell. Because it describes the most likely distance between the nucleus and the electrons, a bigger value of the primary quantum number denotes a larger distance between the nucleus and the electrons.
The form of an orbital is described by the azimuthal (or orbital angular momentum) quantum number. Its value is equal to the total number of angular nodes in the orbital and is indicated by the symbol
‘$l$.'
The magnetic quantum number determines the total number of orbitals in a subshell as well as their orientation. The sign ${m_l}$ is used to represent it. This value represents the projection of the orbital angular momentum along a specific axis.
The values of $n$, $l$, and ${m_l}$ have no bearing on the electron spin quantum number. The symbol ${m_s}$ represents the value of this number, which indicates the direction in which the electron is spinning.
When electrons are added to an atom, three rules apply:
They choose the smallest value of $n$ that is available.
Before receiving a second electron, all orbitals in a subshell must have one electron. In singly occupied orbitals, all electrons have the same spin.
For all four of their quantum numbers, no two electrons can have the same values.

Note:
According to Hund's laws, it is impossible for two electrons in the same atom to have the exact same quantum state or the exact same values of the set of quantum numbers. The stability of an atom's eight electrons is derived from the stability of noble gases, often known as unreactive or noble gases, or the older name inert gases. The periodic table, on the other hand, justifies this statement for second-row elements with an outermost-shell capacity of $8$ electrons.