1. Intermolecular Forces
Understanding the Reason behind the physical and Chemical Behavior of Covalent Molecules

2. The electronegativity of an atom can create a dipole, or polar molecule.
electron rich
region
electron poor
region d+ d-
Polar covalent bond or polar bond :
covalent bond with greater electron density around one of the two atoms

3. Intermolecular forces: attractive forces between molecules.
Intramolecular forces: hold atoms together, attractive forces within a molecule.
Generally, intermolecular forces are much weaker than intramolecular forces.

4. Intermolecular vs Intramolecular
41 kJ to vaporize 1 mole of water (inter)
930 kJ to break all O-H bonds in 1 mole of water (intra)
“Measure” of intermolecular force
boiling point
melting point

5. Dipole-Dipole Forces Attractive forces between polar molecules
Partially + end of one dipole is attracted to the partially -- end of another dipole H F H F H F H F H F

6. Hydrogen Bonding
The hydrogen bond is a special dipole-dipole interaction between they hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom.

7. Decreasing boiling point
Why is the hydrogen bond considered a “special” dipole-dipole interaction?
Decreasing molar mass
Decreasing boiling point

8. Hydrogen Bonding in Water

9. Induced-Dipole Forces
Attractive forces when a polar molecule causes a nonpolar molecule to temporarily have a dipole
induced dipole interaction by polar molecule
induced dipole interaction (by an ion)

10. London Dispersion Forces
Attractive forces between two nonpolar molecules
In polar or nonpolar atoms, electrons are in continuous motion.
At any instant the electron distribution may be uneven. A momentary uneven charge can create a positive pole at one end of an atom of molecule and a negative pole at the other.

11. CH4 is nonpolar: dispersion forces.
What type(s) of intermolecular forces exist between each of the following molecules?
HBr
HBr is a polar molecule: dipole-dipole forces. There are also dispersion forces between HBr molecules.
CH4
CH4 is nonpolar: dispersion forces. S O
SO2
SO2 is a polar molecule: dipole-dipole forces. There are also dispersion forces between SO2 molecules.

12. Properties of Covalent Compounds
Usually soft and squishy
Not soluble in water (usually nonpolar)
Does not conduct electricity
Low melting points
Low boiling points

13. Properties of Ionic Compounds
Combination of ions (cation/anion)
Hard and Brittle
Tightly packed solids in a crystal lattice
Usually soluble in water
Conducts electricity only when dissolved
High melting points

14. Metallic Bonding
Chemical bonding is different in metals than it is in ionic, molecular.
In ionic bonding, a metal and nonmetal(s) are held together by electrostatic forces
In covalent bonding, nonmetals are held together by shared pairs of electrons.
Metallic bonding, however, is the attraction between metal atoms and the surrounding sea of electrons.

15. Metallic Bonding
In a metal, the vacant orbitals in the atoms’ outer energy levels overlap, which allows the outer electrons of the atoms to roam freely throughout the entire metal.
These mobile electrons form a sea of electrons around the metal atoms, which are packed together in a crystal lattice.
I.E. The sea of electrons are delocalized, valence electrons that do not belong to any one atom but move freely about the metal’s network of empty atomic orbitals.

17. Metallic Bonding
The unique characteristics of metallic bonding gives metals their characteristic properties, listed here:
electrical conductivity
thermal conductivity
malleability
ductility
shiny appearance (luster - absorb a wide range of light frequencies )