How are electronegativity values determined?

Hint: In a molecule, when some of the electrons are shared between the atoms make up the molecule. When an atom of a molecule having the ability to attract shared electrons is called electronegativity. When there is a higher electronegativity of an atom, there is the greater ability to attract shared electrons. The electronegativity of atoms can be defined in several ways. The widely accepted method is that developed by Linus Pauling.

Complete step-by-step answer:
Electronegativity of an element can be determined by using the Mulliken scale and to calculate the difference in two elements we use Pauling’s scale of electronegativity. Even Allred Rochow’s scale is used for the calculation of electronegativity of an atom.
Pauling was the first person to explain electronegativity. He calculated the electronegativity difference between two atoms on the bases of the bond energy/ resonance energy of the atoms.
\[{X_A}\, - \,{X_B}\, = \,0.208\sqrt {\Delta AB} \]
Where,
\[\Delta AB\, = \] the resonance of the molecule \[AB\]
According to Mulliken’s electronegativity, the sum of the average value of ionisation potential and electron affinity of an element.
\[{X_M}\, = \,\dfrac{{{\text{Ionisation potential + Electron affinity}}}}{2}\,\]
Where,
\[{X_M}\, = \,\] electronegativity of the \[M\] element.
According to the Allred Rochow’s electronegativity, the force by which the nucleus of an atom attracts the electrons which are on the covalent radius.
\[{X_{(AR)}}\,Electronegativity\,\, = \,\dfrac{{{{\text{Z}}_{{\text{effective}}}}{\text{ }} \times {\text{ }}{{\text{e}}^{\text{2}}}}}{{{r^2}}}\,\]
Where, \[{Z_{effective}} = \] Effective nuclear charge on the atom
\[r = \] radius of the atom

Note: The definition of electronegativity states that the ability of an atom in a chemical bond to polarize electron density towards itself. As we move down to the group the energy level increases and the electrons in a bond get farther away from the nucleus so they are held less tightly. So, electronegativity gets decreased. On the other hand, the atomic number increases sequentially in the same period, and the nuclear charge increases. The electrons are also being added to the valence shell, however, because they add to the same shell, they get shielded to each other very imperfectly. Due to this, the electronegativity increases.