shapes of and bond angles in simple molecules
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- 1. Shapes of and Bond Angles in Simple Molecules
2. Introduction
- In molecules there are 2 types of electron
- 1. Bonding Pairs
- 2. Non-bonding or lone pairs
3.
- pi - bonds have a very limited impact on shape. sigma-bonds have a much more important effect.
4.
- Ionic bonds - non-directional
- Covalent bonds have preferred direction in space
- All covalent compounds have a particular shape
- As a result of spatial distribution of orbitals.
5. VSEPR Theory
- Predict the shapes and bond angles of molecules and molecular ions
- pairs of electrons that surround the central atom of a molecule or ion are arranged as far apart as possible to minimize electron-electron repulsion.
6. VSEPR Theory
- The idea can be used to predict the shapes of molecules by following a simple procedure:
7. VSEPR Theory
- Decide which is the central atom in a molecule.
- In cases of ambiguity, pick the least electronegative atom as this atom will be better able to share its electrons with the other atoms in the molecule.
8. VSEPR Theory
- Count up the valence (outer shell) electrons on the central atom.
- Count up the electrons used by the outer atoms to make bonds with the cental atom.
9. VSEPR Theory
- The sum of ( 2 ) + ( 3 ) divided by two gives the Valence Shell Electron Pair (VSEP) count.
- The predicted geometry of the molecule is based on the number of VSEP.
- i.e. the arrangement of EP around the central atom (both lone pair and bonded pair).
10. VSEPR Theory
- Electrostatic force of repulsion between electron pair.
- Repulsion- to attain most comfortable arrangement.
- Each atom wants an octet of electrons.
11. Types of Repulsion
- Bonding pair- Bonding pair
- Lone pair-bond pair
- Lone pair- lone pair
12. Strength of Repulsion
- Depends on proximity of electron pairs to central atom
- Lone pairs closer to central atom- they are delocalized- have no other nucleus to attract them
- Bond pairs attracted to another nucleus
13. Strength of Repulsion
- Lone pair- Lone pair repulsion > Lone pair- Bond pair repulsion > Bond pair- Bond pair repulsion
14. Effect of Strength
- Lone pairs push bond pairs closer
- Smaller angles result
15. Shapes of Molecules 16. Linear
- 2 bonded pairs
- 0 lone pairs
- Bond angle of 180
- Examples;BeCl2, CO2, HCN, C2H2
17. 18. Trigonal Planar
- 3 bonding pairs
- 0lone pairs
- Bond angle of 120
- Examples; BF3, SO3, NO3-, CO32-, C2H4
19. 20. 21. Tetrahedral
- 4 bonding pairs
- 0 lone pairs
- Bond angle of 109.5
- Examples; NH4+, SO42-, PO43-, Ni(CO)4, CH4
22. 23. 24. Trigonal Pyramidal
- 3 bonding pairs
- 1 lone pair
- Bond angle of 107
- Examples; PH3, SO32-, NH3
25. 26. Bent/ Non-linear
- 2 bonding pairs
- 2 lone pairs
- Bond angle of 105
- Example; H2S, SO2, H2O
27. 28. Trigonal Bipyramidal
- 5 bonding pairs of electrons
- 0 lone pair
- Bond angles of 120 and 90
- Example ; PCl5
29. 30. Octahedral
- 6 bonding pairs
- 0 lone pair
- Bond angle of 90
- Example; SF6
31. 32. 33. Shapes and Bond Anglesof Simple Organic Compounds 34.
- Organic Compounds- consisting of carbon and hydrogen mostly
35. 36. 37. 38. 39. 40. 41. Sp2 Hybridization 42. 43.