Short Answer

Electronegativity is the ability of an atom to attract shared electrons toward itself in a chemical bond. It shows how strongly an atom pulls the bonding electrons. Atoms with high electronegativity attract electrons more strongly, while those with low electronegativity attract them weakly.

Electronegativity helps predict bond type—ionic, polar covalent, or non-polar covalent. It also affects bond polarity, reactivity, and molecular properties. Fluorine is the most electronegative element, while elements like cesium and francium have very low electronegativity.

Detailed Explanation :

Electronegativity

Electronegativity is a fundamental chemical property that describes how strongly an atom attracts electrons in a chemical bond. When two atoms form a bond, the electrons are shared between them, but they are not always shared equally. The atom with higher electronegativity pulls the electron pair closer, resulting in an unequal distribution of electron density. This concept is essential for understanding how molecules form, how they behave, and what type of bonds exist between atoms.

Electronegativity values are used to predict molecular polarity, bond type, acidity, basicity, and the reactivity of many compounds. It also helps explain trends in the periodic table and why some elements are more reactive than others.

1. Definition of Electronegativity

Electronegativity is defined as:
The tendency of an atom to attract shared electrons toward itself in a chemical bond.

Key points:

• It is a relative property, not an absolute one.
• It depends on atomic structure (nuclear charge, size, electron shielding).
• It has no unit; it is expressed as a numeric value.

The most widely used scale is the Pauling scale, where fluorine is assigned the highest value (4.0).

2. Factors That Affect Electronegativity

Electronegativity depends on several atomic properties:

(a) Atomic Size

Smaller atoms have higher electronegativity because their nuclei are closer to the bonding electrons.

(b) Nuclear Charge

Greater positive charge pulls electrons more strongly, increasing electronegativity.

(c) Shielding Effect

Electrons in inner shells reduce the attraction of the nucleus on outer electrons.
More shielding → lower electronegativity.

(d) Effective Nuclear Charge (Z_eff)

Higher effective nuclear charge increases the ability to attract electrons.

Together, these factors determine the strength of an atom’s pull on electrons.

3. Electronegativity Trends in the Periodic Table

Electronegativity shows clear periodic trends:

(a) Across a Period (Left to Right)

Electronegativity increases.

• Atomic size decreases
• Nuclear charge increases
• Attraction for electrons becomes stronger

Example:
Li < Be < B < C < N < O < F

(b) Down a Group (Top to Bottom)

Electronegativity decreases.

• Atomic size increases
• Shielding increases
• Attraction for electrons weakens

Example:
F > Cl > Br > I

Fluorine remains the most electronegative element.

4. Electronegativity and Bond Polarity

Electronegativity difference between two atoms determines bond polarity.

• Small or zero difference → Non-polar covalent bond
• Moderate difference → Polar covalent bond
• Large difference → Ionic bond

Examples:

• H–H: no difference → non-polar
• H–Cl: difference ≈ 0.9 → polar
• Na–Cl: large difference → ionic bond

Thus, electronegativity helps classify bond types.

5. Electronegativity and Molecular Properties

Electronegativity influences:

• Dipole moment: Higher difference → more polarity
• Solubility: Polar molecules dissolve in polar solvents
• Boiling and melting points: Polar molecules interact strongly
• Acidic and basic strength: Related to ability to attract or donate electrons

It also affects the shape and behavior of biomolecules, such as proteins and DNA.

6. Role of Electronegativity in Reactivity

Electronegativity helps predict how substances react.

• Highly electronegative atoms (F, O, N) attract electrons strongly and often act as oxidizing agents.
• Less electronegative atoms (alkali metals) easily lose electrons and act as reducing agents.

Electronegativity differences drive many types of reactions, such as:

• Oxidation–reduction
• Acid–base reactions
• Nucleophilic and electrophilic substitutions

Thus, electronegativity is essential in organic, inorganic, and physical chemistry.

7. Electronegativity in Different Scales

Several scales measure electronegativity:

• Pauling scale (most common)
• Mulliken scale (uses ionization energy and electron affinity)
• Allred–Rochow scale (uses effective nuclear charge)

Although the numeric values differ, the trends remain the same.

8. Electronegativity and Resonance Structures

In molecules with resonance, electronegativity affects how electrons spread.
Highly electronegative atoms pull electron density, influencing resonance stability and bond character.

Example:
In nitrate ion (NO₃⁻), oxygen’s high electronegativity affects electron distribution.

Conclusion

Electronegativity is the ability of an atom to attract shared electrons in a chemical bond. It depends on atomic size, nuclear charge, and shielding effects. Electronegativity trends help explain bond polarity, bond type, molecular behaviour, and reactivity. The greater the electronegativity difference between two atoms, the more polar or ionic the bond becomes. Understanding electronegativity is crucial for predicting chemical properties and reactions.