ChemistryChemical bondingClass 11

Molecular shapes (VSEPR): interactive simulation

VSEPR theory says electron pairs around a central atom push each other as far apart as possible. Count the bond pairs and lone pairs, and the shape follows.

Useful for: JEE Main, NEET, AP Chemistry

Try this

Lone pairs take more room than bond pairs, so they squeeze the bonds together: 109.5° in CH₄ becomes about 107° in NH₃ and 104.5° in H₂O. Rotate each model to see it in three dimensions.

  1. 1

    Step through CH₄, NH₃ and H₂O.

    What you should see

    All three have four electron pairs (sp³), but the bond angle shrinks 109.5° → 107° → 104.5° as lone pairs replace bonds.

  2. 2

    Find the molecules with polar bonds that are still non-polar.

    What you should see

    CO₂, BF₃, CH₄, PCl₅, SF₆ and XeF₄ — their bond dipoles cancel by symmetry.

  3. 3

    Rotate XeF₄ and find its two lone pairs.

    What you should see

    They sit opposite each other (180° apart), leaving the four F atoms in a flat square.

  4. 4

    Rotate PCl₅ until you see the axial and equatorial positions.

    What you should see

    Three equatorial bonds are 120° apart; the two axial bonds are at 90° to them.

Formulas behind it

Steric number

SN=bond pairs+lone pairs\text{SN} = \text{bond pairs} + \text{lone pairs}

Steric number → hybridisation

2→sp, 3→sp2, 4→sp3, 5→sp3d, 6→sp3d22 \to sp,\ 3 \to sp^2,\ 4 \to sp^3,\ 5 \to sp^3d,\ 6 \to sp^3d^2

Repulsion order

lp–lp>lp–bp>bp–bp\text{lp–lp} > \text{lp–bp} > \text{bp–bp}

Common mistakes

  • Naming the shape from the electron geometry. NH₃ has tetrahedral electron geometry but a trigonal pyramidal shape.
  • Forgetting lone pairs on the central atom when counting the steric number.
  • Assuming polar bonds always make a polar molecule.
Practise 2 questionsCheck your answer instantly, with a worked solution.Chemical Bonding chapter guideFormula sheet, solved examples and PYQ patterns.Stuck on a molecular shapes (vsepr) question?Snap it and get a whiteboard video solution.

FAQ

Why is the bond angle of water smaller than that of ammonia?

Water has two lone pairs and ammonia has one. Lone pair–lone pair repulsion is the strongest, so it pushes the O–H bonds closer (104.5°) than the N–H bonds (107°).

What is the hybridisation of XeF₄?

sp³d²: four bond pairs and two lone pairs give a steric number of 6. The shape is square planar.

Is BF₃ polar?

No. Each B–F bond is polar, but the three bond dipoles are 120° apart in a plane and cancel.

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