Chapter 11 – Intermolecular Forces, Liquids, and Solids

Chapter 11 – Intermolecular Forces, Liquids, and Solids

Which factor(s) affect the physical properties of a substance? Why does water boil at 100°C and freeze at 0°C? Why does high pressure and low temperature solidify most gasses? Why can’t hydrogen be solidified? In this unit we will look at the factors that affect the physical properties of liquids and solids.

Intermolecular Forces, Liquids, and Solids

• Intermolecular Forces– Forces of attraction between 2 or more other

molecules in a substance.


• Intermolecular Forces– 3 types: London Dispersion Forces (weakest),

Dipole-Dipole, and Hydrogen Bonding (strongest).


• Intermolecular Forces– London Dispersion Forces: Weak forces of

attractions caused by the attraction between the protons in one molecules and the electrons in another molecule.


• Intermolecular ForcesoLondon Dispersion Forces: • Generally, substances that only have

LDF’s have low melting and vaporization points. • But substances with higher molecular

weights can have so many LDF’s that they will have high melting and vaporization points.


• Intermolecular Forceso London Dispersion Forces:

Halogen Molecular Weight

(amu)Boiling Point (K)

F2 38.0 85.1

Cl2 71.0 238.6

Br2 159.8 332.0

I2 253.8 457.6


• Intermolecular Forceso London Dispersion Forces:

Noble Gas Molecular Weight

(amu)Boiling Point (K)

He 4.0 4.6

Ne 20.2 27.3

Ar 39.9 87.5

Kr 83.8 120.9


• Intermolecular Forceso Dipole - Dipole Forces: Weak forces of attractions

caused by the attraction between the oppositely charged poles of two or more molecules.


• Intermolecular Forceso Dipole - Dipole Forces: Therefore, dipole-dipole

interactions only develop within polar substances.


• Intermolecular Forceso Hydrogen Bonding: Forces of attractions between a

hydrogen atom of one molecule and a fluorine, oxygen, or nitrogen, of another molecule.


• Intermolecular Forceso Hydrogen Bonding: Ammonia’s trigonal pyramidal

shape allows the hydrogen atoms of one molecule to be attracted to the nitrogen on another.


• Intermolecular Forceso Hydrogen Bonding:


• Intermolecular Forceso Hydrogen Bonding:

o Ice is less dense than liquid water due to hydrogen bonding.

oWhen H-Bonding is maximized in the formation of ice, large open spaces are created.


• Intermolecular Forces

Interacting Molecules or ion

Polar Molecules? Ions Present? Polar Molecules and Ions Present?

LDF’s Diplole H-Bonding Ion-Dipole Ionic Bonding Dipole

Weakest IMF’s -------------------------------> Strongest IMF’s


• Properties of Liquidso Viscosity – The measure of the resistance of a liquid to

flow.


• Properties of Liquidso Viscosity – Affect by temperature and molecular weight.

Temperature – IMF’s are overcome with higher temperature.Molecular Weight – The larger the molecule, the more

‘tangled’ it becomes, thus resisting flow.


• Properties of Liquidso Surface Tension – A measure of the inward forces that

must be exerted to overcome to expand the surface of a liquid.


• Properties of Liquidso Surface Tension – Cohesive vs Adhesive Forces

Cohesive Forces – Forces among molecules in a liquid due to IMF’s.

Adhesive Forces – Forces between the molecules of a substance and the surface of a material.


• Phase Changes


• Phase Changeso Heat of Fusion (ΔHfus): The amount of energy to melt 1 mole of a

substance. o What patter do you see in the heat of fusion of these substances?

ΔHfus H2O = 6.01 kJ / mol

ΔHfus C4H10 = 5.00 kJ / mol

ΔHfus Hg = 23.0 kJ / mol


• Phase Changeso Heat of Vaporization (ΔHvap): The amount of energy to vaporize 1

mole of a substance.oWhat pattern do you see in the heat of vaporization of these

substances?

ΔHvap H2O = 40.7 kJ / mol

ΔHvap C4H10 = 24.0 kJ / mol

ΔHvap Hg = 58.0 kJ / mol


• Heating curves and Cooling Curves


• Cooling Curve for Solutions


• Phase Diagrams

Phase Diagrams for Carbon Dioxide


• Phase Diagrams


• Phase Diagrams• Triple Point – The combination of temperature

and pressure that a substance exists as a solid, liquid, and a gas at the same time.

• Critical point – The maximum temperature by which a substance can not longer be liquified


• Vapor Pressure• The pressure exerted by the gas above a liquid once

dynamic equilibrium has been established between the liquid molecules and gas molecules.


• Vapor Pressure• Dynamic Equilibrium – The rate of evaporation equals

the rate of condensation.


• Vapor Pressure vs Intermolecular Forces• The stronger the IMF’s, the more difficult it is for a

molecule to escape to the gas phase. Therefore its vapor pressure will be lower.

• The weaker the IMF’s, the higher the vapor pressure.


• Vapor Pressure


• Solids• Amorphous Solids: Solids that lack any molecular

organization.

Intermolecular Forces, Liquids, and Solids• Solids• Crystalline Solids:

– Solids that have a high degree of molecular organization.– Crystals are three-dimensional shapes that have flat surfaces and

angled corners.

Intermolecular Forces, Liquids, and Solids• Solids• Crystalline Solids: Geodes

Intermolecular Forces, Liquids, and Solids• Solids• Crystalline Solids: – Unit Cells: The repeating three-dimensional shape of a

crystalline solid.– Crystal Lattice: Many unit cells making an overall crystal.


• Solids• Crystalline Solids: –All ionic compounds can be explained with 7 different

types of unit cells.

–We will take a close look at 3 common types; primitive cubic, body-centered cubic, and face-centered cubic.


• Crystalline Solids• Primitive Cubic


• Crystalline Solids• Body-Centered Cubic


• Crystalline Solids


• Crystalline SolidsClose Packing Spheres


• Crystalline SolidsCoordination Number – The number of

particles that surround one specific particle in solid.


• Crystalline SolidsCoordination Number – What is the

coordination numbers for the following examples?


• Crystalline SolidsHollow Spheres

Rice University (1985): A 60-Carbon hollow ball of carbon is discovered.



These structures were called buckminsterfullerenes or ‘buckyballs’.

Buckminster Fuller: Architect who created geodome shapes.



These structures were called ‘buckyballs’.Buckminster Fuller: Architect who created

geodome shapes.



Buckyballs are found in nature and even been identified in deep outer space in clouds surrounding stars.



Buckyballs have potential uses in medicine, lubricants, and computers.


• Crystalline SolidsBuckminsterfullerenes

Nanotubes


• Covalent Network SolidsMolecular substances in which all of the atoms

are connected by a network of covalent bonds.


• Covalent Network SolidsDiamonds versus graphite


• Summary of Crystalline solids

Type of Solid Particles Forces Properties Examples

Molecular Atoms or Molecules

LDF, dipole-dipole, H-Bonding

Soft, low melting points

Ar, CH4, CO2, ice

Covalent Network

Atoms connected by

covalent bonds

Covalent Bonds Very hard, very high metltng

points

Diamonds, quartz, graphite,

glass (SiO2)

Ionic Cations and anions

Electrostatic Interactions

Hard, brittle, high melting

points

NaCl, Ca(NO3)2

Metallic atoms Metallic Bonds Soft or hard, low or high melting

points

Cu, Fe, Al

Chapter 11 – Intermolecular Forces, Liquids, and Solids

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