Symmetry-Adapted Orbitals for Polyatomic Molecules · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Matching orbitals by symmetry

Science · Chemistry · ages 19-20
Name ______________________   Date ____________

  1. What is a symmetry label for?

    • It counts the electrons in the set
    • It decides which central orbital a set may mix with
    • It names the molecule

  2. What is the first move when building the orbital diagram for water?

    • Combine the hydrogen orbitals into same-label sets
    • Hybridise the oxygen atom
    • Fill electrons from the top down

  3. Which hydrogen combinations appear in water?

    • Two identical a1 pairs
    • One a1 pair plus one lone hydrogen
    • An in-phase a1 pair and an out-of-phase b2 pair

  4. A ligand combination matches no central atom orbital. What becomes of it?

    • It vanishes from the diagram
    • It stays at starting energy as nonbonding and can hold a lone pair
    • It climbs to the highest level

  5. In water, which oxygen orbitals meet the a1 hydrogen pair?

    • 2s and 2pz
    • 2py only
    • None, it stays nonbonding

  6. Methane's four hydrogen 1s orbitals give one a1 set plus a t2 trio. Type the total number of combinations.

    Answer: ______________

  7. When filling a finished diagram, you place electrons starting from the top level.

    Circle one:   True   False

  8. A student pairs the b2 hydrogen set of water with oxygen 2s. What is the mistake?

    • Oxygen 2s is already full
    • Hydrogen sets never mix at all
    • Labels must match, and 2s is a1 while the set is b2
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Answer key

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

Matching orbitals by symmetry W1-mt_llEYzYuutf-s1

  1. It decides which central orbital a set may mix with · Matching labels are the permission rule for mixing.
  2. Combine the hydrogen orbitals into same-label sets · Grouping outer orbitals by symmetry comes before any mixing.
  3. An in-phase a1 pair and an out-of-phase b2 pair · Two hydrogens give one symmetric and one antisymmetric combination.
  4. It stays at starting energy as nonbonding and can hold a lone pair · No partner means no mixing, so the energy never shifts.
  5. 2s and 2pz · Oxygen offers 2s and 2pz of a1 type to that pair.
  6. 4 · One plus three gives four combinations from four orbitals.
  7. False · Levels fill from the bottom up, like any Aufbau process.
  8. Labels must match, and 2s is a1 while the set is b2 · The b2 set may only meet the b2 orbital, which is 2py.
Worksheet · LightMySky