Chemistry · Periodic Classification Of Properties · NEET
NCERT names exactly three: the Pauling scale, the Mulliken-Jaffe scale, and the Allred-Rochow scale. All three try to put a number on the same idea — how strongly an atom pulls shared electrons. NEET questions almost always use the Pauling scale because it is the most widely used. Just remember the names in order; you rarely need the deep math.
Electronegativity is not a real, measurable lab quantity like ionization enthalpy or electron gain enthalpy. It is a comparison idea. So scientists built number scales so we can say 'atom A pulls harder than atom B'. The scales let us compare atoms and predict if a bond will be polar or non-polar. This is why NEET calls it a qualitative measure with numerical scales attached.
Pauling built his scale from bond energies (how much energy holds bonds together) and set fluorine = 4.0 as the reference. Mulliken built his from the atom itself: he took the average of the ionization enthalpy and the electron gain enthalpy of the atom. So Pauling uses bonds, Mulliken uses the lone atom's energy values. Both give almost the same order of atoms.
Mulliken said an atom that both loses electrons hard (high ionization enthalpy) and gains electrons easily (high electron gain enthalpy or electron affinity) must pull shared electrons strongly. So he took the average: electronegativity is roughly (ionization enthalpy + electron affinity) / 2. This is why it is called the Mulliken-Jaffe scale. For NEET, know the concept, not exact values.
Use the Pauling scale. NCERT clearly says it is the most widely used, and NEET gives you Pauling values (fluorine 4.0, oxygen 3.5, nitrogen 3.0, chlorine 3.0). Ordering questions like 'arrange in increasing electronegativity' are all based on Pauling values and on the periodic trend (increases across a period, decreases down a group).
Yes, mostly. The actual numbers differ (a value on Pauling is not the same number on Mulliken), but the ranking of atoms from weak-puller to strong-puller comes out almost the same. Fluorine is the most electronegative on all scales. So for exam ordering questions, the choice of scale does not change your answer.
Arrange the following elements in increasing order of electronegativity: N, O, F, C, Si.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Linus Pauling, an American scientist, made it in 1932 (NCERT notes 1922 as his early work on the idea). He set fluorine, the strongest electron-puller, at 4.0 as the reference point and scaled everything else below it.
Fluorine attracts shared electrons more strongly than any other element. Pauling arbitrarily fixed it at 4.0 to be the top of his scale, so every other element gets a lower value. This makes 4.0 the maximum on the Pauling scale.
You only need to know its name as one of the three scales NCERT lists. The Allred-Rochow scale bases electronegativity on the electrostatic force the nucleus exerts on a bonding electron. NEET does not ask its formula; it only tests that you know the three scale names and that Pauling is the main one.
Electron gain enthalpy is a measurable energy for a lone gas atom gaining one electron. Electronegativity is a non-measurable tendency of a bonded atom to pull the shared electron pair. One is about a free atom; the other is about an atom inside a compound.
On the Pauling scale it is a relative number with no units. The Mulliken scale can be expressed in energy units (like eV) because it averages ionization and electron gain energies, but the common Pauling values you use in NEET are unitless.
