What is electronegativity?

Short Answer

Electronegativity is the ability of an atom to attract shared electrons in a chemical bond. It determines how electron density is distributed in molecules.

  • Atoms with high electronegativity, like fluorine and oxygen, strongly attract electrons and often form polar bonds.
  • Atoms with low electronegativity, like sodium and potassium, weakly attract electrons and usually form ionic or non-polar bonds.
Detailed Explanation :

Definition of Electronegativity

Electronegativity (EN) is a measure of the tendency of an atom to attract electrons toward itself when it is chemically bonded to another atom. It is a dimensionless property introduced by Linus Pauling, often represented on the Pauling scale, with values ranging from 0.7 (cesium) to 4.0 (fluorine).

  • High electronegativity → strong pull on shared electrons.
  • Low electronegativity → weak pull on shared electrons.

Electronegativity explains bond polarity, molecular shape, and chemical reactivity.

Factors Affecting Electronegativity

  1. Atomic Number (Nuclear Charge):
    • More protons → stronger pull on electrons → higher electronegativity.
  2. Atomic Radius:
    • Smaller radius → electrons closer to nucleus → higher electronegativity.
    • Larger radius → electrons farther from nucleus → lower electronegativity.
  3. Electron Shielding:
    • Inner electrons reduce effective nuclear pull on bonding electrons → lower electronegativity.
  4. Electron Configuration:
    • Elements with nearly full valence shells (like halogens) attract electrons strongly → high EN.
    • Elements with single valence electron (like alkali metals) attract weakly → low EN.

Trends in the Periodic Table

Across a Period (Left to Right):

  • Electronegativity increases.
  • Reason: Nuclear charge increases, atomic radius decreases → stronger attraction for shared electrons.
  • Example: Lithium (EN 0.98) → Fluorine (EN 3.98)

Down a Group (Top to Bottom):

  • Electronegativity decreases.
  • Reason: Atomic radius increases, shielding increases → weaker attraction for shared electrons.
  • Example: Fluorine (EN 3.98) → Iodine (EN 2.66)

Significance of Electronegativity

  1. Predicting Bond Type:
    • Large difference in EN → ionic bond (e.g., NaCl).
    • Small difference in EN → polar covalent bond (e.g., HCl).
    • No difference → non-polar covalent bond (e.g., Cl₂).
  2. Bond Polarity and Molecular Polarity:
    • Determines dipole moment and reactivity of molecules.
  3. Chemical Reactivity:
    • High EN → atoms attract electrons → strong oxidizing agents (e.g., F₂).
    • Low EN → atoms lose electrons easily → strong reducing agents (e.g., Na).
  4. Physical Properties:
    • Affects boiling point, solubility, and intermolecular interactions.
  5. Industrial Applications:
    • Helps in designing chemicals, drugs, and materials based on bond polarity.

Examples

  • Fluorine (F): EN 3.98 → strongest attraction for electrons → highly reactive non-metal.
  • Oxygen (O): EN 3.44 → forms polar covalent bonds (e.g., H₂O).
  • Sodium (Na): EN 0.93 → weakly attracts electrons → forms ionic compounds.
Conclusion

Electronegativity is the ability of an atom to attract bonding electrons. It increases across a period due to higher nuclear charge and smaller atomic radius and decreases down a group due to increased atomic size and shielding. Electronegativity is essential for predicting bond type, molecular polarity, chemical reactivity, and physical properties of elements and compounds.