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🧪 Chemistry  ·  Chemical Bonding and Molecular Structure  ·  NEET & JEE

Why is F-F bond energy (159 kJ/mol) unexpectedly low compared to Cl-Cl (243 kJ/mol)?

Answer: Lone pair-lone pair repulsion between the very close F atoms weakens the bond.

  • A Lone pair-lone pair repulsion between the very close F atoms weakens the bond
  • B Fluorine generally has a lower atomic number than chlorine in typical laboratory settings
  • C The F-F bond has significant ionic character unlike Cl-Cl under usual circumstances
  • D Chlorine atoms are larger, which directly strengthens their bond according to most researchers

Correct answer: A. Lone pair-lone pair repulsion between the very close F atoms weakens the bond

Explanation: Fluorine atoms are tiny; adjacent lone pairs on the two F atoms experience intense repulsion, weakening the F-F bond.

Linear180 deg, e.g. CO2Trigonal Planar120 deg, e.g. BF3Tetrahedral109.5 deg, e.g. CH4Trigonal Bipyramidale.g. PCl5Octahedrale.g. SF6

VSEPR theory predicts molecular shape from the number of bonding and lone electron pairs around the central atom.

Concept context

Understand how atoms join to form molecules. Covers ionic and covalent bonding, VSEPR theory, hybridization (sp, sp², sp³), molecular orbital theory, bond polarity, and intermolecular forces like hydrogen bonding.

Read the full Chemical Bonding and Molecular Structure notes →