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3.6.1: Bond Strength (Problems)

  • Page ID
    235763
  • PROBLEM \(\PageIndex{1}\)

    Which bond in each of the following pairs of bonds is the strongest?

    a. C–C or \(\mathrm{C=C}\)
    b. C–N or \(\mathrm{C≡N}\)
    c. \(\mathrm{C≡O}\)
    or \(\mathrm{C=O}\)
    d. H–F or H–Cl
    e. C–H or O–H
    f. C–N or C–O

    Answer a

    \(\mathrm{C=C}\)

    Answer b

    \(\mathrm{C≡N}\)

    Answer c

    \(\mathrm{C≡O}\)

    Answer d

    H–F

    Answer e

    O–H

    Answer f

    C–O

    PROBLEM \(\PageIndex{2}\)

    When a molecule can form two different structures, the structure with the stronger bonds is usually the more stable form. Use bond energies to predict the correct structure of the hydroxylamine molecule:

    Two Lewis structures are shows with the word “or” written in between them. The left structure shows a nitrogen atom with one lone pair of electrons single bonded to two hydrogen atoms. It is also bonded to an oxygen atom with two lone pairs of electrons. The oxygen atom is bonded to a hydrogen atom. The right structure shows a nitrogen atom single bonded to three hydrogen atoms and an oxygen atom with three lone pairs of electrons.

    Answer

    The greater bond energy is in the figure on the left. It is the more stable form.

    PROBLEM \(\PageIndex{3}\)

    Use principles of atomic structure to answer each of the following:1

    a. The radius of the Ca atom is 197 pm; the radius of the Ca2+ ion is 99 pm. Account for the difference.
    b. Given these ionization values, explain the difference between Ca and K with regard to their first and second ionization energies.

    Element First Ionization Energy (kJ/mol) Second Ionization Energy (kJ/mol)
    K 419 3050
    Ca 590 1140

    c. The first ionization energy of Mg is 738 kJ/mol and that of Al is 578 kJ/mol. Account for this difference.

    Answer a

    When two electrons are removed from the valence shell, the Ca radius loses the outermost energy level and reverts to the lower n = 3 level, which is much smaller in radius.

    Answer b

    Removal of the 4s electron in Ca requires more energy than removal of the 4s electron in K because of the stronger attraction of the nucleus and the extra energy required to break the pairing of the electrons. The second ionization energy for K requires that an electron be removed from a lower energy level, where the attraction is much stronger from the nucleus for the electron. In addition, energy is required to unpair two electrons in a full orbital. For Ca, the second ionization potential requires removing only a lone electron in the exposed outer energy level.

    Answer c

    In Al, the removed electron is relatively unprotected and unpaired in a p orbital. The higher energy for Mg mainly reflects the unpairing of the 2s electron

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