Molecular Shapes from Electron Pair Repulsion · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Pairs push shapes into place

Science · Matter & Materials · ages 15-16
Name ______________________   Date ____________

  1. What is step one of any shape prediction?

    • Sketch the Lewis structure first
    • Guess the colour first
    • Weigh the sample first

  2. What is the single VSEPR rule?

    • Pairs attract each other closely
    • Pairs spread as far apart
    • Pairs ignore each other fully

  3. Methane is tetrahedral with angles near 109.5 degrees.

    Circle one:   True   False

  4. Why is water bent tighter still than ammonia?

    • Water has no lone pairs
    • Bonds push lone pairs away
    • Two lone pairs squeeze even harder

  5. Why is the bond angle in ammonia smaller than in methane?

    • Its lone pair squeezes the bonds closer
    • It has more atoms in total
    • It is drawn with brighter ink

  6. How do you read wedges and dashes in a sketch?

    • Wedge out, dash back
    • Wedge means broken bond
    • Dash means double bond

  7. A sketch shows four pairs but a flat square shape. What is wrong?

    • Nothing, squares suit four pairs
    • Recheck the Lewis structure
    • Angles no longer matter

  8. A double-bonded molecule confuses a student counting pairs. What is the fix?

    • Count every shared electron separately
    • Count each bond direction once
    • Skip the Lewis structure
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Answer key

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

Pairs push shapes into place W1-mt_Of6ZxYjOsn-s1

  1. Sketch the Lewis structure first · Dots and lines give the pair count everything else rests on.
  2. Pairs spread as far apart · Repulsion spaces pairs out, and that spacing sets the shape.
  3. True · Four bonding pairs and no lone pairs give that shape.
  4. Two lone pairs squeeze even harder · Two lone pairs narrow the angle a lot, leaving the smallest of the three.
  5. Its lone pair squeezes the bonds closer · One lone pair pushes harder than a bonding pair, narrowing the angle.
  6. Wedge out, dash back · Those two marks lift the sketch into three dimensions.
  7. Recheck the Lewis structure · Four pairs with no lone pairs means tetrahedral in 3D, not a flat square.
  8. Count each bond direction once · Single, double and triple bonds each count as one repulsion direction.
Worksheet · LightMySky