Multiple Bonds (DP IB Chemistry): Revision Note

Alexandra Brennan

Written by: Alexandra Brennan

Reviewed by: Richard Boole

Updated on

Multiple bonds

  • Non-metal atoms can share more than one pair of electrons to form single, double, or triple covalent bonds

  • Sharing electrons allows both atoms to achieve a noble gas configuration

    • This increases the stability of the atoms

  • The type of covalent bond relates directly to the number of shared electrons:

    • Single bond (C–C) = 2 shared electrons

    • Double bond (C=C) = 4 shared electrons

    • Triple bond (C≡C) = 6 shared electrons

  • Quadruple covalent bonds are not possible

    • The repulsion between 8 electrons between the two nuclei is too great

Bond energy

  • Bond energy is the amount of energy required to break one mole of a covalent bond in the gaseous state

    • Bond energy has units of kJ mol-1

  • It is a measure of bond strength:

    • The higher the bond energy, the stronger the bond

Bond length

  • Bond length is the distance between the nuclei of two covalently bonded atoms

  • As more electrons are shared, the electron density between the atoms increases

    • This increases the electrostatic attraction between the bonding electrons and the nuclei

  • The stronger attraction pulls the atoms closer together

    • This means that:

      • Bond length decreases

      • Bond strength increases

  • Triple bonds are the shortest and, therefore, the strongest covalent bonds

    • This is due to the high electron density between the nuclei

Carbon-carbon bond lengths

Diagram comparing carbon-carbon bond lengths and energies: single bond 147 pm, 347 kJ/mol; double bond 134 pm, 614 kJ/mol; triple bond 120 pm, 839 kJ/mol.
Triple bonds are the shortest covalent bonds and therefore the strongest ones

Examiner Tips and Tricks

Remember:

  • Single bonds = longest and weakest

  • Triple bonds = shortest and strongest

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Alexandra Brennan

Author: Alexandra Brennan

Expertise: Chemistry Content Creator

Alex studied Biochemistry at Newcastle University before embarking upon a career in teaching. With nearly 10 years of teaching experience, Alex has had several roles including Chemistry/Science Teacher, Head of Science and Examiner for AQA and Edexcel. Alex’s passion for creating engaging content that enables students to succeed in exams drove her to pursue a career outside of the classroom at SME.

Richard Boole

Reviewer: Richard Boole

Expertise: Chemistry Content Creator

Richard has taught Chemistry for over 15 years as well as working as a science tutor, examiner, content creator and author. He wasn’t the greatest at exams and only discovered how to revise in his final year at university. That knowledge made him want to help students learn how to revise, challenge them to think about what they actually know and hopefully succeed; so here he is, happily, at SME.

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