Hybridisation, Conjugation and Delocalisation in Organic Molecules · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Hybrids set shape, sharing sets character

Science · Chemistry · ages 18-19
Name ______________________   Date ____________

  1. Why does a conjugated system have to be planar to work?

    • Parallel p orbitals must overlap along the chain
    • Flat molecules dissolve more easily
    • Double bonds are shorter than single bonds

  2. Each carbon of ethene has three sigma partners. What is its hybridisation?

    • sp3
    • sp
    • sp2

  3. What bond angle do you predict around an sp3 carbon?

    • 90 degrees
    • 109.5 degrees
    • 180 degrees

  4. Two anion resonance forms differ only in where the negative charge sits. Which is more stable?

    • The form with the negative charge on oxygen
    • The form with the negative charge on carbon
    • Both forms are always exactly equal

  5. Why does the carbon to nitrogen link of an amide resist rotation?

    • It spins freely like any single bond
    • It resists rotation through partial double character
    • It breaks apart when twisted

  6. Ethyne carbons are sp hybridised. What shape do you predict?

    • Bent near 109.5 degrees
    • Flat near 120 degrees
    • Straight at 180 degrees

  7. A measured bond length lands halfway between single and double. What do you conclude?

    • Its pi electrons are delocalised over several atoms
    • It was measured at the wrong temperature
    • Single bonds always stretch over time

  8. A student draws a resonance form with one atom shifted. What is the error?

    • Yes, resonance always moves whole atoms
    • No, only electron positions may differ
    • Yes, if the moved atom is carbon
LightMySky · lightmysky.comW1-mt_Anv0MSQ4hq-s1

Answer key

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

Hybrids set shape, sharing sets character W1-mt_Anv0MSQ4hq-s1

  1. Parallel p orbitals must overlap along the chain · Pi overlap needs parallel p orbitals, and only a flat chain supplies them.
  2. sp2 · Three sigma partners leave one p orbital for the pi bond.
  3. 109.5 degrees · Four sp3 hybrids point at tetrahedron corners.
  4. The form with the negative charge on oxygen · Negative charge prefers the more electronegative home.
  5. It resists rotation through partial double character · Delocalisation lends the link pi character, which blocks twisting.
  6. Straight at 180 degrees · Two sp hybrids point in opposite directions.
  7. Its pi electrons are delocalised over several atoms · In between lengths are the signature of shared pi electrons.
  8. No, only electron positions may differ · Atom positions are fixed. Only electrons roam between forms.
Worksheet · LightMySky