1. Molecular Geometry & Bonding Theories
Chapter 9
Molecular Geometry & Bonding Theories

2. Overview Molecular Shapes VSEPR Model Polarity of Molecules
Predicting Shapes
Effect of Nonbonding Electrons
Polarity of Molecules
Covalent Bonding

3. Hybrid Orbitals Multiple Bonds Molecular Orbitals sp, sp2, sp3
hybrids containing d orbitals
Multiple Bonds
sigma (s) & pi (p)
localized & delocalized
Molecular Orbitals
electron configurations & bond order
diamagnetism & paramagnetism

4. Molecular Shapes & VSEPR
Shapes defined by bond angles
linear, 180° angles
trigonal planar, 120° angles
tetrahedral, 109.5° angles
VSEPR
Valence Shell Electron Pair Repulsion theory
electron pairs are arranged symmetrically with maximum separation

5. Two electron pairs
180° apart
linear geometry
180° •

6. Three electron pairs
120° apart
trigonal planar geometry •
120°

7. Four electron pairs
109.5° apart
tetrahedral geometry •
109.5°

8. Five electron pairs • angles of 90° and 120°
trigonal bipyramidal (TBP) geometry
90° •
120°

9. Six electron pairs
angles of 90°
octahedral geometry
90° •

10. Geometries Electron pair geometry Molecular Geometry
arrangement of electron pairs around a central atom
Molecular Geometry
arrangement of atoms around a central atom
When all electron pairs are bonding pairs
electron pair geometry = molecular geometry
When there are unshared electron pairs
electron pair geometry ¹ molecular geometry

11. To determine electron pair geometry
draw Lewis dot structure
count shared & unshared electron pairs around central atom
a multiple bond is counted as only one bonding pair when predicting geometry
determine electron pair geometry based on the number of electron pairs
2 pair = linear
3 pair = trigonal planar
4 pair = tetrahedral
5 pair = trigonal bipyramidal
6 pair = octahedral

12. Molecular Geometries with One or More Unshared Pairs
Two Pairs
electron pair geometry linear
bonding pairs
non-bonding pairs
molecular geometry linear

13. Two electron pairs
molecular geometry
electron pair geometry
180° •

14. Three Pairs electron pair geometry trigonal planar bonding pairs 3 2
non-bonding pairs
molecular geometry trig. pl bent

15. Three electron pairs • molecular geometry electron pair geometry
trigonal planar
trigonal planar • •
bent
120°

16. Four Pairs electron pair geometry tetrahedral bonding pairs 4 3 2
non-bonding pairs
molecular geometry tet trig. pyr. bent

17. Four electron pairs • tetrahedral molecular geometry
electron pair geometry •
trigonal pyramid •
109.5° •
bent •

18. Five Pairs electron pair geometry trigonal bipyramid
bonding pairs
non-bonding pairs
molecular geometry tbp seesaw T-shp. Lin.

19. Five electron pair • 90° electron pair geometry molecular geometry TBP
seesaw
120° • • • •
T-shaped •
linear

20. Six Pairs electron pair geometry octahedral bonding pairs 6 5 4 2
non-bonding pairs
molecular geometry oct sq.pyr. sq. pl. lin.

21. Six electron pairs • electron pair geometry 90° molecular geometry
octahedral •
square pyramid • • •
square planar • •
linear

22. Molecular Polarity
Molecules are always non-polar if all covalent bonds are non-polar
N2, P4, Cl2
Molecules with polar bonds can be polar or non-polar
H - Cl polar bond, polar molecular
O=C=O two polar bonds but total molecule is non-polar

23. H Cl O C O equal but opposite forces cancel out Þ non-polar moleculed+ d-
H Cl
equal but opposite forces cancel out Þ non-polar molecule d+ d- d-
O C O

24. O H no yes are these dipole moments equal & opposite?
is this molecule polar?

25. Cl Cl C Cl Cl yes no are these bond dipole moments equal & opposite?
is this molecule polar?

26. H H C Cl Cl no yes are these bond dipole moments equal & opposite?
is this molecule polar?

27. Single and Multiple Bonds
s (sigma) bonds
always the first bond between two atoms
single bonds are localized between two atoms
orbitals from two atoms overlap, allowing electrons to be shared
electron density is on the internuclear axis C •
localized electrons

28. C C p (pi) bonds • • the second & third bonds between two atoms
p bond electrons can be delocalized over several atoms to form resonance structures
electron density is above & below the internuclear axis
electron density can move or delocalize C • •
electron density above & below--p bond
internuclear axis C

29. Hybridization allows for greater number of bonds
types of hybridization
sp mixing of one s orbital & one p orbital
­¯ ­ ­ ­ ­ ­ ­ 2s p sp p
sp2 mixing of one s orbital & two p orbitals
­¯ ­ ­ ­ ­ ­ ­ 2s p sp p
sp3 mixing of one s orbital & three p orbitals
­¯ ­ ­ ­ ­ ­ ­ 2s p sp3

30. in sp hybridization in sp2 hybridization in sp3 hybridization
the two sp hybrid orbitals form two s bonds with linear geometry
remaining two p orbitals form p bonds
in sp2 hybridization
the three hybrid orbitals form three s bonds with trigonal planar geometry
the remaining one p orbital forms a p bond
in sp3 hybridization
the four hybrid orbitals form four s bonds with tetrahedral geometry
sp3 hybrid atoms can form no p bonds as they have no unhybridized p orbitals

31. Molecular Orbitals mathematical combinations of atomic orbitals
delocalized over whole molecule
n atomic orbitals produce n molecular orbitals
½ are bonding orbitals and ½ are antibonding orbitals
bond order
# bonding electrons - # antibonding electron

32. electron configuration of diatomic, homonuclear molecules s. p. p s s
electron configuration of diatomic, homonuclear molecules s * p * p s s * s
MO’s from p orbital combination
MO’s from s orbital combination

33. electron configuration of diatomic, homonuclear molecules with interaction of the 2s and 2p orbitals s * p * s p s * s
relative positions switched

34. s * p * s p s * s s * p * s p s * s H2 N2 B.O. = 1 B.O. = 3
2 electrons
10 electrons

35. s * p * s p s * s s * p * p s s * s He2 O2 B.O. = 0 B.O. = 2
4 electrons
12 electrons