NSS chemistry Book 3 chapter_25

Chapter 25 Simple molecular substances with non-octet structures and shapes of simple molecules

Class Practice

A25.1

(a) BCl3

NCl3

IF3

(b) BCl3. The central boron atom has only six outermost shell electrons. IF3. The central iodine atom has 10 outermost shell electrons.

A25.2 Molecule No. of Spatial No. of lone No. of Shape electron arrangement pairs bond pairs pairs of electron pairs 4 Tetrahedral CH4 0 4 Tetrahedral 3 NH3 4 Trigonal Tetrahedral 1 pyramidal 4 V-shaped H2O 2 Tetrahedral 2 © Aristo Educational Press Ltd. 2010 1

HKDSE CHEMISTRY  A Modern View (Chemistry) Coursebook 3

Chapter 25 Simple molecular substances with non-octet structures and shapes of simple molecules

Chapter Exercise

1. eight 2. eight 3. six 4. 10 5. 12

6. non-octet 7. linear, 180°

8. trigonal planar, 120° 9. tetrahedral, 109.5°

10. trigonal bipyramidal, 90°, 120° 11. octahedral, 90° 12. 2, 2 13. 1, 3 14. shapes 15. D 16. B 17. C 18. A 19. D 20. A

21. 22.

(a) (b) (c) (a) (b) (c)

A: ; B: A: WZ3 B: YZ3

A. The central atom (W) has only six electrons in its outermost shell. X: Trigonal pyramidal Y: Trigonal bipyramidal 107° 90°(for Cl(axial) PCl(equatorial) bond angles) and 120° (for ClPCl bond angles within the plane of triangle)

23. (a)

(b)

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HKDSE CHEMISTRY  A Modern View (Chemistry) Coursebook 3

24. (a) SO2:

(b) (c)

SO3: SO2: V-shaped

SO3: Trigonal planar

Since there are three groups of electrons around the central atoms (sulphur) in both SO2 and SO3, all the O=S=O bond angles are about 120°.

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