1. Ch. 6.5b Hybrid Orbitals and Intermolecular Forces
Chemical Bonding

2. POINT > Describe the concept of hybrid orbitals
POINT > Describe 4 types of intermolecular forces
POINT > Review polar covalent bonding
POINT > Relate intermolecular forces to changes of state

3. POINT > Describe the concept of hybrid orbitals
Previously you learned that methane (CH4) has a tetrahedral geometry with all bond angles = 109.5ᵒ
You have also learned that the four valence e- of a carbon atom have a 2s22p2 arrangement
This is a problem. How can 4 e- in different sublevels, with different energies, result in four identical bonding orbitals?

4. Linus Pauling (1916 – 1994) TWO Introduced: Hybrid orbitals
Nobel Prizes!!
Introduced:
Hybrid orbitals
Concept of electronegativity
Idea that most covalent bonds have some ionic character
Resonance structures

5. POINT > Describe the concept of hybrid orbitals
Orbital hybridization: Several (different) atomic orbitals combine to form the same number of equivalent hybrid bonding orbitals
Carbon 
2s22p2
2s12p3 
Mix to form four equal sp3 hybrid orbitals

6. POINT > Describe the concept of hybrid orbitals
Methane (CH4)

7. WB CHECK:
When a carbon atom is bonded to four atoms, as in carbon tetrachloride CCl4
the s and p orbitals of C each get 2 Cl
the s and p orbitals of C form two hybrid orbitals
the s and p orbitals of C form 4 hybrid orbitals
the s and p orbitals of C overlap

8. Linus Pauling won his first Nobel Prize for his work
WB CHECK:
Linus Pauling won his first Nobel Prize for his work
on DNA structure
on chemical bonding
on atomic structure
on opposition to nuclear bomb testing

9. Linus Pauling won his second Nobel Prize for his work
WB CHECK:
Linus Pauling won his second Nobel Prize for his work
on DNA structure
on chemical bonding
on atomic structure
on opposition to nuclear bomb testing

10. POINT > Describe 4 types of intermolecular forces
Covered so far:
Ionic bonding in ionic compounds
Metallic bonding in metals and alloys
Covalent bonding that holds atoms together in molecules
A variety of weaker forces exist between molecules and affect the properties of molecular compounds

11. POINT > Review polar covalent bonding
Polar covalent bonds: atoms share electrons unequally due to electronegativity (EN) differences
More EN atom: stronger pull on e- = slight (-) charge
Less EN atom: slight (+) charge

12. POINT > Review polar covalent bonding
We use delta (δ) to denote atoms that acquire partial charges in polar molecules

13. POINT > Review polar covalent bonding
Ex. Hydrogen Chloride (HCl) δ+ δ- H Cl
EN = 2.1
EN = 3.0

14. POINT > Review polar covalent bonding
Hydrogen Chloride (HCl) H Cl
EN = 2.1
EN = 3.0

15. POINT > Review polar covalent bonding
Polar bonds result in a dipole: Any bond having two poles (charged regions)

16. POINT > Review polar covalent bonding
Ex. Water (H2O) δ-
EN = 3.5 O δ+ δ+ H H
EN = 2.1
EN = 2.1

17. POINT > Review polar covalent bonding
Ex. Water (H2O)
EN = 3.5 O H H
EN = 2.1
EN = 2.1

18. POINT > Review polar covalent bonding
One end of a dipole is slightly negative, the other end slightly positive
Dependent on shape of molecule

19. POINT > Review polar covalent bonding
Ex. Carbon dioxide (CO2) vs. water (H2O) H O
EN = 2.1
EN = 3.5
Dipoles Cancel O C
Nonpolar Molecule
Polar Molecule
EN = 3.5
EN = 2.5
EN = 3.5

21. POINT > Describe 4 types of intermolecular forces
Forces between molecules (from strongest to weakest)
Ion-dipole forces: Ion-dipole forces occur when ionic compounds are dissolved in water
The charged ions interact with the dipoles of the water molecules

22. Ion-dipole interactions
POINT > Describe 4 types of intermolecular forces
Ion-dipole interactions

23. POINT > Describe 4 types of intermolecular forces
2. Hydrogen bonding*: Compounds with O-H, N-H and F-H bonds can form hydrogen bonds
The polarity of these bonds and the small size of hydrogen atoms causes strong attractions
Hydrogen bonds create surface tension in water
They hold molecules, like the two strands of DNA, together
* These are not bonds. They are intermolecular forces

24. POINT > Describe 4 types of intermolecular forces
Hydrogen bonding

25. WB CHECK:
What type of intermolecular force would occur between H2O and MgCl2?
What type of intermolecular force would occur between H2O and NH3?

26. Ex. HCl, HBr, H2S POINT > Describe 4 types of intermolecular forces
3. Dipole-dipole forces: These are interactions between polar molecules with out O-H, N-H or F-H bonds
Ex. HCl, HBr, H2S

28. POINT > Describe 4 types of intermolecular forces
4. London dispersion forces (LDF): These are the weakest intermolecular forces
LDFs occur when a polar molecule induces a temporary dipole in an otherwise nonpolar molecule

30. CHECK:
Rank order the intermolecular forces, from strongest to weakest: (LDF = London dispersion force)
a) dipole-dipole, H bonding, LDF, ion-dipole
b) ion-dipole, dipole-dipole, H bonding, LDF
c) LDF, ion-dipole, dipole-dipole, H bonding
d) ion-dipole, dipole-dipole, H bonding, LDF
e) ion-dipole, H bonding, dipole-dipole, LDFWB

31. POINT > Relate intermolecular forces to changes of state
Intermolecular forces govern properties of substances (like boiling point)
Interactions that tend to hold molecules together result in higher boiling and melting points

33. Bonding and intermolecular forces overview
Strongest
Weakest
Metallic bonding
Covalent bonding
Ionic bonding
Ion-dipole
Hydrogen bonding
Dipole-dipole
London dispersion
intermolecular forces

34. WB CHECK:
What is the strongest intermolecular force that would be present in CH4?
ion-dipole
hydrogen bonding
dipole-dipole
LDF

35. WB CHECK:
What is the strongest intermolecular force that would be present in Br2?
ion-dipole
hydrogen bonding
dipole-dipole
LDF

36. WB CHECK:
What is the strongest intermolecular force that would be present in H2O?
ion-dipole
hydrogen bonding
dipole-dipole
LDF

37. WB CHECK:
What is the strongest intermolecular force that would be present in HCl?
ion-dipole
hydrogen bonding
dipole-dipole
LDF

38. WB CHECK:
What is the strongest intermolecular force that would be present in a mixture of ethanol (C2H5OH) and water?
ion-dipole
hydrogen bonding
dipole-dipole
LDF

39. Homework:
Read and re-read 6.5 pages
F.A. #4-6 page 197