1. Ch. 6.5 Molecular Structure
(p )

2. 6.5 Molecular Geometry
Properties of molecules depend upon:
1) Kinds of elements present & how much of each.
2) Bonding - types & strengths
3) Geometry - arrangement or structure

3. Molecular Geometry
2 Ways to predict Molecular Geometry
1) VSEPR - Valence Shell Electron Pair Repulsion
This indicates that electrostatic repulsion between valence shell electrons will cause them to be as far apart from each other as possible.
2) Hybridization –
mixing of 2 or more orbitals (usually S & P) of similar energies on the same atom to give new orbitals of equal energies.

4. A. VSEPR Theory Valence Shell Electron Pair Repulsion Theory
Electron pairs orient themselves in order to minimize repulsive forces.

5. Lone pairs repel more strongly than bonding pairs!!!
A. VSEPR Theory
Types of e- Pairs
Bonding pairs –shared pairs that form bonds
Lone pairs - nonbonding e- pairs
Lone pairs repel more strongly than bonding pairs!!!

6. A. VSEPR Theory Bond Angle
Lone pairs reduce the bond angle between atoms.
Bond Angle

7. VSEPR THEORY DEFINITION
VSEPR Theory classifies molecules using LETTERS ~{“A” FOR CENTRAL ATOM,”B” for what is bonded to central atom “a” & #’s to indicate electron pairs surrounding a central atom, whether in a bond OR as a “lone pair” of e-

8. MOLECULAR GEOMETRY

9. AB2, A is central atom, 2 B’s are the surrounding atoms, shape is linear.
AB3 , A is central atom, B are again the surrounding atoms, 3 this time, and to fully separate shape is trigonal-planar
AB4, A remains as the central atom, B again are the 4 surrounding atoms, shape to maximize distance apart becomes tetrahedral.

10. Molecular Geometry

11. Molecular Geometry
AB5, Triangular Bipyramidal
AB6, Octahedral

12. Molecular Geometry
Sometimes, molecules have lone pair(s) of electrons. These unshared pairs can cause bending (repulsion) of bonded pairs, (E stands for unshared pair). ..
AB2E - Bent shape, SnCl2 Sn
Cl Cl
AB3E - Triangular pyramidal, NH3 N
H H H
....
AB2E2 - Bent, H2O O
H H

13. B. Determining Molecular Shape
Draw the Lewis Diagram.
Tally up e- pairs on central atom.
double/triple bonds = ONE pair
Shape is determined by the # of bonding pairs and lone pairs.
Know the 8 common shapes
& their bond angles!

14. C. Common Molecular Shapes
2 total 2 bond 0 lone
BeH2
LINEAR
180°

15. C. Common Molecular Shapes
3 total 3 bond 0 lone
BF3
TRIGONAL PLANAR
120°

16. C. Common Molecular Shapes
3 total 2 bond 1 lone
SnF2
BENT
<120°

17. C. Common Molecular Shapes
4 total 4 bond 0 lone
CH4
TETRAHEDRAL
109.5°

18. C. Common Molecular Shapes
4 total 3 bond 1 lone
NH3
TRIGONAL PYRAMIDAL
107°

19. C. Common Molecular Shapes
4 total 2 bond 2 lone
H2O
BENT
104.5°

20. C. Common Molecular Shapes
5 total 5 bond 0 lone
PCl5
TRIGONAL BIPYRAMIDAL
120°/90°

21. D. Examples
F P F F
PF3
4 total
3 bond
1 lone
TRIGONAL PYRAMIDAL
107°

22. Molecular Geometry
2) Hybridization - mixing of 2 or more orbitals(usually S & P) of similar energies on the same atom to give new orbitals of equal energies.
Methane CH4 - provides a good example(1s22s22p2)
__↓ __↓ __ __ _
C 1s 2s 2px 2py 2pz
4 valence electrons(2s2 & 2p2) combine or hybridize into 4 new identical orbitals __ __ _ __
sp3

23. Molecular Geometry
Each sp3 orbital has equal energy and are 109.5o apart in a tetrahedron.
Hybridization also explains bonding & geometry in molecules formed by Group 15 & 16 elements.

24. Each sp3 orbital has equal energy and are 109
Each sp3 orbital has equal energy and are 109.5o apart in a tetrahedron.

25. D. Examples
O C O
CO2
2 total
2 bond
0 lone
LINEAR
180°

26. 6.5 MOLECULAR GEOMETRY Intermolecular Forces
Forces of attraction between molecules:
1) usually weaker than bonds
a) Dipole-dipole forces
b) Induced dipole
c) Hydrogen Bonding
d) London Dispersion Forces

27. Dipole-dipole forces
Strongest intermolecular forces are between polar molecules.
Equal but opposite charges separated by a small distance creates a dipole.
Dipole-dipole forces are the attraction between polar molecules.
Negative region of one molecule attracts positive region of the other.
Sometimes causes higher boiling pts.

28. Induced dipole
A polar molecule can induce a dipole in a nonpolar molecule by momentarily attracting electrons.
**These forces are less or weaker than true dipole-dipole forces.
These forces are responsible for O2, a nonpolar molecule to dissolve in water, a polar molecule.

29. INDUCED DIPOLE H+
O O = O-

30. Hydrogen Bonding
Type of bonding between a hydrogen atom and an unshared pair of electrons of a strongly electronegative atom of another molecule
Causes the high boiling point and surface tension of water. +H
O-----+H +H
+H O-

31. London Dispersion Forces
Weak intermolecular forces caused by constantly moving electrons and the creation of instantaneous and induced dipoles.
Present in all atoms & molecules.
The only force in noble gases & nonpolar molecules.
Increases with atomic mass, molecular mass.

32. MOLECULAR POLARITY Molecular Polarity is determined by
1) polarity of bonds - diatomic
and
2) orientation(Geometry) of atoms –
Linear, Bent, Triangular, Pyramidal, Tetrahedral

33. NONPOLAR MOLECULE
In some molecules, bond dipoles oppose one another causing zero polarity. Cl
CCl Cl-C-Cl also CO2 O=C=O

34. + - H Cl A. Dipole Moment Direction of the polar bond in a molecule.
Arrow pointing from + to –.
H Cl + -

35. B. Determining Molecular Polarity
Depends on:
bond polarity
molecular shape
Possibilities:
NP bonds  NP molecule
Polar bonds  NP molecule
Polar bonds  Polar molecule

36. B. Determining Molecular Polarity
Polar bonds  NP molecule
Dipole moments are symmetrical and cancel out.
BF3

37. B. Determining Molecular Polarity
Polar bonds  Polar molecule
Dipole moments are asymmetrical and don’t cancel .
H2O

38. B. Determining Molecular Polarity
Polar molecules have...
polar bonds AND
asymmetrical shape &/or atoms
CCl3F

41. STRUCTURAL FORMULA HCl H2O C2H6
Indicates KIND’S, NUMBERS’S & ARRANGEMENT(GEOMETRY) of bonds in a molecule ….
H - Cl O H - C - C- H H H
HCl H2O C2H6

42. MULTIPLE COVALENT BONDS
DOUBLE BOND
H H H H
C : : C or C = C

43. Triple covalent bond N2 : N ::: N : or :N = N:
C2H2 H: C ::: C :H or H - C = C - H