Question

Which set of quantum numbers ( $n\,,\,l,\,\,m,\,s$ ) represent the outermost electron in a gaseous aluminium atom.
A.$2,1,0, + \dfrac{1}{2}$
B.$2,1. - 1, + \dfrac{1}{2}$
C.$3,0,0, + \dfrac{1}{2}$
D.$3,1, - 1, + \dfrac{1}{2}$

Answer 1

Hint:
Principal quantum number can be defined as the last shell in which the electron goes and Angular momentum quantum number defines the orbital in which the electron is. Magnetic quantum number is a range from the positive value of angular momentum to the negative

Complete step by step answer:
Let us understand what these quantum numbers are
Principal quantum number is given by $n$
It is equal to the period number of the given element. It represents the last shell of the atom. It is also equal to the period number.

Angular momentum quantum number is given by $l$
It represents the orbital in which the last electron is present.
It is mathematically equal to

Magnetic quantum number
This is given by $m$ . it is not a number but a range of possible values.
It is mathematically equal to
$m = + l\,to\, - l$

Spin quantum number
This is given by $s$ . It is given by $ \pm \dfrac{1}{2}$ .
Quantum number is given for only one electron. Every electron in an atom will have a different value for quantum numbers. Quantum numbers are like an address for an electron.

For aluminum
The configuration is
$1{s^2}2{s^2}2{p^6}3{s^2}3{p^1}$
So its values, will be
$n = 3$ since it is in the third period.
$l = 1$ since it is in p orbital
$m = - 1$
$s = + \dfrac{1}{2}$
Hence the correct option is OPTION D.


Note:Quantum numbers are an address for the electron. They can describe the exact position of electrons. If the quantum numbers are known, we can tell about the period it is in, the shell, its magnetic moment and spin. These numbers are unique to an electron.