Anand Classes brings you detailed study material on Electronegativity, an essential concept in Chemistry for JEE, NEET, and CBSE Board exams. Electronegativity explains the ability of an atom to attract shared electrons in a chemical bond and plays a vital role in understanding bond polarity, reactivity, and periodic trends. This comprehensive guide covers the definition, Pauling scale, Mulliken scale, other electronegativity scales, FAQs, and applications with easy-to-understand explanations for students. Click the print button to download study material and notes.
Electronegativity
Electronegativity provides a qualitative measure of the ability of an atom in a chemical compound to attract a shared pair of electrons towards itself.
We know that a covalent bond is formed by the mutual sharing of electrons between two atoms. However, not all covalent bonds are identical in nature. To explain these differences, Linus Pauling introduced the concept of electronegativity.
👉 Definition:
Electronegativity is the tendency of an atom of an element to attract the shared pair of electrons towards itself in a covalent bond.
- Greater the electronegativity of an atom, greater is its ability to pull the shared pair of electrons towards itself.
- Fluorine is the most electronegative element in the periodic table.
It must be remembered that, unlike other atomic properties such as ionisation enthalpy or electron gain enthalpy (which are properties of isolated gaseous atoms), electronegativity is a property of bonded atoms.
Electronegativity values are not directly measurable; they are obtained indirectly by various methods. As a result, several relative scales of electronegativity have been proposed, such as:
- Pauling Scale
- Mulliken–Jaffe Scale
- Allred–Rochow Scale
Among these, the Pauling scale is the most widely used.
Pauling Scale of Electronegativity
In 1932, Linus Pauling proposed the first electronegativity scale, based on bond enthalpies of heteronuclear bonds.
He suggested that:
- If two atoms (A and B) have the same electronegativity values, then the bond enthalpy of the A–B bond should equal the geometric mean of the bond enthalpies of A–A and B–B bonds.
$$E_{AB} = \sqrt{E_{AA} \times E_{BB}}$$
This assumption is valid for pure covalent bonds.
However, Pauling observed that for most A–B bonds, the actual bond enthalpy was higher than the geometric mean. This indicates that the two atoms have different tendencies to attract the shared electrons, i.e., they have different electronegativities.
The difference between the actual bond enthalpy $E_{AB}$ and the calculated geometric mean $\sqrt{E_{AA} \times E_{BB}}$ is called the excess bond enthalpy (ΔE).
👉 Relation between Electronegativity and Excess Bond Enthalpy $$|\chi_A – \chi_B| = 0.102 \, \sqrt{\Delta E} \quad \text{(in eV)}$$
or equivalently in kJ mol⁻¹, $$|\chi_A – \chi_B| = 0.12 \, \sqrt{\Delta E}$$
Thus, a large difference between $E_{AB}$ and the geometric mean implies a large electronegativity difference between atoms A and B.
Pauling assigned the highest value of 4.0 to fluorine, and the electronegativity values of other elements were calculated relative to it. These values are widely used.
⚠ Limitation:
The main drawback of the Pauling scale is that bond enthalpies are not accurately known for all elements, making the values approximate and relative.
Mulliken Scale of Electronegativity
Robert Mulliken proposed another useful scale of electronegativity based on ionization enthalpy and electron gain enthalpy.
- The tendency of an atom to lose electrons depends on its ionization enthalpy.
- The tendency to gain electrons depends on its electron gain enthalpy.
Thus, an atom with:
- High ionization enthalpy and a large (negative) electron gain enthalpy → strongly attracts electrons → highly electronegative.
- Low ionization enthalpy and a less negative electron gain enthalpy → weak attraction for electrons → low electronegativity.
👉 Mulliken Electronegativity Formula: $$\chi_M = \frac{\Delta H_i + \Delta H_{eg}}{2}$$
where,
- ΔHi = Ionization enthalpy
- ΔHeg = Electron gain enthalpy
This approach gives a more physical picture, as the tendency to attract shared electrons is logically the average of:
- The atom’s ability to hold its own electrons (ΔHi)
- Its ability to attract an extra electron (ΔHeg)
Other Scales of Electronegativity
In addition to Pauling and Mulliken, other scales have also been proposed, such as:
- Allred–Rochow Scale (based on effective nuclear charge and covalent radius)
- Sanderson’s Scale (based on electron density and stability ratios)
FAQs on Electronegativity
Q1. What is electronegativity?
👉 Electronegativity is the tendency of an atom in a covalent bond to attract the shared pair of electrons towards itself.
Q2. Who introduced the concept of electronegativity?
👉 The concept was introduced by Linus Pauling in 1932, who also proposed the first quantitative scale of electronegativity.
Q3. Which element is the most electronegative and what is its value?
👉 Fluorine is the most electronegative element, with a value of 4.0 on Pauling’s scale.
Q4. How is electronegativity different from electron gain enthalpy?
👉 – Electronegativity refers to the tendency of a bonded atom to attract shared electrons.
👉 – Electron gain enthalpy refers to the energy released when an isolated gaseous atom gains an electron.
Thus, electron gain enthalpy is a property of isolated atoms, while electronegativity is a property of bonded atoms.
Q5. On what factors does electronegativity depend?
👉 Electronegativity depends on:
- Atomic size (smaller atoms → higher electronegativity)
- Nuclear charge (greater charge → stronger attraction)
- Screening effect (less shielding → higher electronegativity)
- Bonding environment (sp³ < sp² < sp hybridized atoms due to s-character).
Q6. Why is electronegativity not a measurable property?
👉 Unlike ionisation enthalpy or electron gain enthalpy, electronegativity cannot be measured directly for isolated atoms. It is a relative property, derived indirectly using methods such as Pauling, Mulliken, or Allred–Rochow scales.
Q7. What is the main difference between Pauling and Mulliken scales?
👉
- Pauling Scale: Based on bond enthalpies of covalent bonds.
- Mulliken Scale: Based on the average of ionization enthalpy and electron gain enthalpy.
Q8. How does electronegativity vary across the periodic table?
👉
- Across a period: Increases (due to smaller atomic radius and higher nuclear charge).
- Down a group: Decreases (due to larger size and shielding effect).
Q9. Why is fluorine more electronegative than oxygen?
👉 Fluorine has:
- Smaller atomic radius
- Higher effective nuclear charge
- Stronger attraction for bonding electrons
Hence, fluorine is more electronegative.
Q10. What are the applications of electronegativity?
👉 Electronegativity helps in:
- Predicting the nature of bonds (covalent, polar covalent, or ionic)
- Explaining bond polarity
- Understanding reactivity trends in elements
- Interpreting the acidic/basic character of oxides and hydrides
✅ Summary:
- Electronegativity is the ability of an atom in a bond to attract shared electrons.
- Fluorine is the most electronegative element (value = 4.0 on Pauling scale).
- Pauling Scale (bond enthalpy based) is the most widely used, though approximate.
- Mulliken Scale (based on ionization enthalpy and electron gain enthalpy) provides a more physical explanation.
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