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Chemistry 20

Chemistry 20 · Worksheets

Chemical bonding

Ten questions of mixed difficulty, covering Bonding. Print it, or work through it on screen — the answer key starts on its own page.

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Chemical bonding

Chemistry 20 · maddyhelps.com

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Circle the best answer for each question. Show your work in the space provided.

  1. A compound formed between a metal and a non-metal is usually

    1. a) ionic, and held together by shared pairs of electrons
    2. b) molecular, and held together by metallic bonding
    3. c) molecular, and held together by the attraction between ions
    4. d) ionic, and held together by the attraction between oppositely charged ions

  2. Of these two molecules, the polar one is

    1. a) CO₂, because its C=O bonds are polar
    2. b) H₂O, because its bent shape leaves the bond dipoles uncancelled
    3. c) neither, because both are symmetrical
    4. d) both, because both contain polar bonds

  3. The strongest intermolecular force acting between water molecules is

    1. a) ionic bonding
    2. b) hydrogen bonding
    3. c) covalent bonding
    4. d) London dispersion

  4. The Lewis structure of CO₂ contains

    1. a) two carbon–oxygen double bonds, in a linear arrangement
    2. b) two carbon–oxygen single bonds, in a bent arrangement
    3. c) one double and one single bond
    4. d) two carbon–oxygen triple bonds

  5. Of these substances, the one expected to have the lowest melting point is

    1. a) MgO
    2. b) CH₄
    3. c) CaF₂
    4. d) NaCl

  6. The shape of an ammonia molecule, NH₃, is

    1. a) bent
    2. b) tetrahedral
    3. c) trigonal pyramidal
    4. d) trigonal planar

  7. Ranked from lowest to highest boiling point, the correct order is

    1. a) H₂S < CH₄ < H₂O
    2. b) H₂O < H₂S < CH₄
    3. c) CH₄ < H₂O < H₂S
    4. d) CH₄ < H₂S < H₂O

  8. Carbon tetrachloride, CCl₄, has polar C–Cl bonds, yet the molecule is non-polar because

    1. a) the molecule is linear
    2. b) its tetrahedral shape makes the four bond dipoles cancel
    3. c) chlorine and carbon have the same electronegativity
    4. d) the lone pairs on chlorine cancel the dipoles

  9. Sodium chloride is a hard solid with a melting point of 801 °C because

    1. a) sodium and chlorine atoms are unusually heavy
    2. b) the ions are free to move throughout the solid
    3. c) the Na–Cl molecules are held together by strong covalent bonds
    4. d) every ion is pulled on by several oppositely charged neighbours in a lattice

  10. A covalent bond forms when two atoms

    1. a) share a pair of electrons
    2. b) are both metals
    3. c) transfer a pair of electrons
    4. d) exchange protons

Answer key · Chemical bonding

Chemistry 20 · maddyhelps.com

  1. d) ionic, and held together by the attraction between oppositely charged ions — Metals lose electrons easily and non-metals gain them, so electrons transfer rather than being shared. The result is positive and negative ions pulling on each other. Sharing is what non-metals do with other non-metals.
  2. b) H₂O, because its bent shape leaves the bond dipoles uncancelled — Both contain polar bonds, but polarity of a molecule depends on shape as well. Carbon dioxide is linear, so its two dipoles point in exactly opposite directions and cancel. Water is bent, so they add to give a net dipole.
  3. b) hydrogen bonding — Hydrogen bonded to oxygen, nitrogen or fluorine produces an unusually strong dipole attraction. Note that this is a force between molecules — the O–H covalent bonds inside a water molecule are a different and much stronger thing.
  4. a) two carbon–oxygen double bonds, in a linear arrangement — Carbon has four valence electrons and each oxygen needs two more, so carbon forms a double bond to each oxygen. With two bonding groups and no lone pairs on carbon, VSEPR puts them as far apart as possible: 180° apart, linear.
  5. b) CH₄ — The other three are ionic and have to break a whole lattice to melt. Methane is molecular, so melting only has to overcome the weak forces between separate molecules — its covalent C–H bonds stay intact.
  6. c) trigonal pyramidal — Nitrogen has four electron groups — three bonds and one lone pair — so the groups point to the corners of a tetrahedron. Shape is named for the atoms only, and with one corner occupied by a lone pair the three hydrogens form a pyramid.
  7. d) CH₄ < H₂S < H₂O — Methane is non-polar, so only weak dispersion forces hold it together. Hydrogen sulfide is polar but does not hydrogen bond. Water does, and that is why it is still liquid at room temperature while the other two are gases.
  8. b) its tetrahedral shape makes the four bond dipoles cancel — Four identical bonds pointing to the corners of a tetrahedron pull equally in every direction, so the vector sum is zero. Symmetry is what decides this, which is why the shape has to be worked out before polarity can be.
  9. d) every ion is pulled on by several oppositely charged neighbours in a lattice — An ionic solid is not made of molecules. Each ion sits in a three-dimensional lattice surrounded by ions of opposite charge, and melting it means breaking all of those attractions at once, which takes a great deal of energy.
  10. a) share a pair of electrons — Two non-metals both want to gain electrons, so neither can take them outright. Sharing lets both count the pair towards a full outer shell.