Intermolecular forces

p. 45

Ion-induced Dipole forces

An ion that is close to an atom or molecule, canturn the electron cloudand cause a temporary

dipole

-

Dipole-Dipole forcesSimilar to hydrogen forces,

but weaker dipoles.

Dipole-induced Dipole forces

A dipole that is close to an atom or molecule, canturn the electron cloudand cause a temporary

dipole

Induced dipole forces

(London forces) Temporary dipole.Very weak forces.

Hydrogen bondsH bond with N, O, F

NH3, H2O, HF

Relatively strong bonds

Metals Ionic crystal

structures

Molecules

• Metal bonds • Electrostatic

forces

• Hydrogen

bonds

• Van der Waals

forces(Dipole-dipole, Ion-

dipole and London

forces)

Cu Cu Cu Cu Cu Cu

Cu Cu Cu Cu Cu Cu

Cu Cu Cu Cu Cu Cu

Mg

O

Mg

O

Mg

O

Mg

O

Mg

O

Mg

O

H F

HomeworkExercise 5p. 433, 8, 11

3.1 Forces that prevent ice blocks to adopt the shape of the container?

3.2 Forces overcome when ice melts

3.3 Forces overcome when water evaporates?

3.4 Forces overcome when converting water into a gas state of hydrogen gas and oxygen gas.

3. Which type of force - between atoms or between molecules are involved in the following?

Intermolecular

Intermolecular

Intermolecular

Interatomic

11. Arrange the following in order of increasing strength of intermolecular forces in the pure matter. Ne, CH4, CO and CCl4. Give a reason for your answer.

Ne - London (weak)

CH4 - London (weak)

CO - dipole-dipole (weak)

CCl4 - London (weak)

3. Complete the following table.

Compound Intermolecular force Weak or strong

3.1 HBr

3.2 HF

3.3 SO2

3.4 CO2

3.5 H2O

Dipole-dipoleWeak

Hydrogen bonds Strong

Dipole-dipoleWeak

London forces Weak

Hydrogen bonds Strong

4. Complete the following table.

Elements Type of interatomic bonds Formula

4.1Sodium and

chlorine

4.2Magnesium and

oxygen

4.3Hydrogen and

oxygen

4.4Carbon and

oxygen

4.5 Copper atoms

Ionic bondNaCl

Ionic bond MgO

Covalent bond H2O

Covalent bond CO2

Metal bond Cu

4. Complete the following table.

Elements Type of interatomic bonds Formula

4.6 Carbon atoms

4.7Hydrogen and

fluorine

4.8One iron and one

oxygen atom

4.9Magnesium and

chlorine

4.10Calcium and

chlorine

Covalent bondC

Covalent bond HF

Ionic bond FeO

Ionic bond MgCl2

Ionic bond CaCl2

Phases of molecules p 47Solid – strong forces

Phases of molecules Solid - heated

Phases of molecules Solid - melting

Phases of molecules Liquid – start to flow

Phases of molecules Gas – weak forces between particles

Size of molecules

F Cl Br I

• More electrons• Stronger dipole• Stronger intermolecular forces(Size of molecule only influences Van der Waals forces)

DensityDensity decreases when strength of intermolecular forces decreases

Water is an exception

Boiling and melting pointsStronger intermolecular forces --> more energy is needed to overcome the intermolecular forces.Boiling and melting points increase.

Cl

H

ViscosityViscosity is an indication of the fluidity of a substance(NB. it is not the fluidity of the substance!)

Thermal expansionExpansion when material is heated.E.g. train tracks, thermometers...

HomeworkExercise 6p. 595, 6, 8.1, 8.2, 13

5.1

5.2

5.3

6.1

6.2

8.1

8.2

13

5. Choose from the following list the substance that best matches the description.

Br2, I2, F2, N2, O2, Cl25.1 Highest boiling point

5. Choose from the following list the substance that best matches the description.

Br2, I2, F2, N2, O2, Cl25.2 Highest melting point

5. Choose from the following list the substance that best matches the description.

Br2, I2, F2, N2, O2, Cl25.3 Greatest intermolecular force

5. Choose from the following list the substance that best matches the description.

Br2, I2, F2, N2, O2, Cl25.4 Largest molecule

5. Choose from the following list the substance that best matches the description.

Br2, I2, F2, N2, O2, Cl25.5 Arrange according to decreasing size of atom

I2, Br2, Cl2, F2, O2, N2

5. Choose from the following list the substance that best matches the description.

Br2, I2, F2, N2, O2, Cl25.5 Arrange according to increasing strength of intermolecular forces

N2, O2, F2, Cl2, Br2, I2

6. Consider the following substances.

Cu, S, NH3, NaBr6.1 Which of the substances is the best conductor of electricity at room temperature?

6. Consider the following substances.

Cu, S, NH3, NaBr6.2 Which of the substances has the lowest boiling point?

6. Consider the following substances.

Cu, S, NH3, NaBr6.3 Which of the substances has hydrogen bonds between molecules?

7. Study the following graph showing the melting points of hydrogen halides.

7.1 Explain why HF has a higher melting point than HCl.

The intermolecular forces in HF are stronghydrogen bonds.The intermolecular forces in HCl are weak Van der Waals forces.Hydrogen bonds are stronger than Van der Waals forces. Therefore HF has a higher boiling point, because more energy is needed to break the intermolecular forces.

7. Study the following graph showing the melting points of hydrogen halides.

7.2 Give a reason for the tendency of increasing melting points after HCℓ, moving down in the group.

The intermolecular forces in HCℓ, HBr and HI are Van der Waals forces which increase with increasing molar mass. The melting points increase with increasing strength in intermolecular forces. Stronger forces need more energy to be broken.