Isomerism: Same Formula, Different Molecule · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Same formula, different molecule

Science · Chemistry · ages 16-17
Name ______________________   Date ____________

  1. Pentane and 2,2-dimethylpropane share C5H12. What are they?

    • The same substance drawn twice
    • Chain isomers
    • Position isomers

  2. What does a molecular formula tell you?

    • How the atoms are joined together
    • Which atoms, and how many of each
    • Which isomer the sample is

  3. Butan-1-ol and butan-2-ol are which kind of isomers?

    • Chain isomers
    • Position isomers
    • Functional group isomers

  4. A molecular formula alone is enough to identify which isomer you hold.

    Circle one:   True   False

  5. In CHCl=CHCH3, the Cl on one carbon and the CH3 on the other carbon sit on opposite sides of the double bond. Is this isomer E or Z?

    • Z, because the top groups sit on opposite sides
    • Neither, priority only matters for chains
    • E, because the top groups sit on opposite sides

  6. Propan-1-ol, CH3CH2CH2OH, and methoxyethane, CH3OCH2CH3, share C3H8O. Why do they behave so differently?

    • They are in different families
    • One has more atoms than the other
    • One is a mixture and the other is pure

  7. Why can a double bond produce stereoisomers?

    • The pi bond stops rotation
    • Double bonds contain fewer electrons
    • Double bonds always break and reform

  8. A student calls but-1-ene and but-2-ene chain isomers. What is the error?

    • They are position isomers
    • They are not isomers at all
    • They are E-Z isomers of each other
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Same formula, different molecule W1-mt_DvD0coeKZe-s1

  1. Chain isomers · Their carbon skeletons connect differently, so they are chain isomers.
  2. Which atoms, and how many of each · A molecular formula counts atoms but hides the connections.
  3. Position isomers · Same skeleton and group, different carbon, means position isomers.
  4. False · One formula can describe several different molecules.
  5. E, because the top groups sit on opposite sides · On one carbon Cl outranks H; on the other CH3 outranks H. Those top groups sit on opposite sides, so the isomer is E.
  6. They are in different families · Same atoms arranged as different functional groups behave nothing alike.
  7. The pi bond stops rotation · The pi bond stops rotation and freezes arrangements in place.
  8. They are position isomers · Both have a straight four-carbon chain. Only the position of the double bond changes, so they are position isomers.
Worksheet · LightMySky