Multiple Bonds (DP IB Chemistry: SL): Revision Note

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

• Non-metal atoms do not form quadruple covalent bonds

  • Two atoms can overlap their s and p orbitals to form at most one σ bond and two π bonds, so a fourth shared pair is not possible between non-metal atoms

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

• Between the same two atoms, triple bonds are the shortest and the strongest covalent bonds

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

Carbon-carbon bond lengths