VSEPR Theory Molecular Shapes - UNSOLVED PRACTICE SET

Q7. State the basic postulate of VSEPR theory. What does it predict about the arrangement of electron pairs? 

Q8. Predict the shapes of the following molecules using VSEPR theory:

(a) BeCl₂

(b) BF₃

Q9. Why is the bond angle in NH₃ (107°) less than the tetrahedral angle (109.5°)?

Q10. Why is the bond angle in H₂O (104.5°) even smaller than in NH₃?

Q11. Your teacher arranges four students at the corners of a square in the classroom, then asks them to move so they are as far from each other as possible. They end up at the corners of a tetrahedron. Explain how this is analogous to VSEPR theory, and why lone pairs would make the arrangement slightly different from a perfect tetrahedron. 

Q12. Predict the shape of SF₄ using VSEPR theory. What is the name of this shape?

Q13. Explain VSEPR theory and its application in predicting molecular shapes. Discuss how lone pairs affect bond angles. Predict the shapes and bond angles of:

(a) CH₄

(b) NH₃

(c) H₂O

(d) PCl₅

Illustrate with diagrams.

Q14. Describe the different molecular geometries possible based on the number of electron pairs around a central atom. Create a table showing:

Number of electron pairs

Number of bond pairs

Number of lone pairs

Shape of molecule

Examples

Explain why lone pair-lone pair repulsion > lone pair-bond pair repulsion > bond pair-bond pair repulsion. 

Q15. During a molecular model-making activity, your team builds models of various molecules using balloons or plastic balls.

(a) You use two balloons to represent BeCl₂. What shape do they form? Why is the bond angle 180°?

(b) You add a third balloon for BF₃. What shape results? What happens when you replace one bond pair with a lone pair (as in SO₂)?

(c) With four balloons, you get a tetrahedron for CH₄. But when one balloon represents a lone pair (NH₃), the shape changes. Why does the lone pair push the bonds closer together?

(d) Your team attempts to build SF₆ using six balloons. What shape emerges? Why is this shape possible for sulphur but not for oxygen?

Q16. Complete the following table using VSEPR theory:

Q17. The following molecules have the indicated number of electron pairs around the central atom. Predict their shapes and bond angles:

(a) XeF₂: 5 electron pairs (3 lone pairs, 2 bond pairs)

(b) XeF₄: 6 electron pairs (2 lone pairs, 4 bond pairs)

(c) XeF₆: 7 electron pairs (1 lone pair, 6 bond pairs)

(d) ICl₄⁻: 6 electron pairs (2 lone pairs, 4 bond pairs)

For each, draw a rough sketch showing the positions of lone pairs and bond pairs.

Q18. Consider the following series of molecules: CH₄, NH₃, H₂O, HF.

(a) All have 8 valence electrons around the central atom (or the only atom). Predict the shape of each.

(b) The bond angles decrease from CH₄ (109.5°) to NH₃ (107°) to H₂O (104.5°). Calculate the total decrease in bond angle from CH₄ to H₂O.

(c) Explain this trend in terms of lone pair repulsion using VSEPR theory.

(d) HF has no bond angle to measure (it's diatomic). But if you consider the "lone pair space" around fluorine, how many lone pairs does F have? What would be the approximate angle between any two lone pairs?