Intermolecular Forces Solids & Liquids

Warm-Up If 8 g of hydrogen and 32 g of methane (CH4) are injected into an empty, rigid 100 L container at a temperature of 100oC, determine the following: The partial pressure of each gas. The total pressure in the container. The mole fraction of each gas. How many times faster hydrogen would effuse than methane.

Liquids and Solids Intermolecular Forces (IMF) Force of attraction between molecules in liquids and solids Intramolecular forces (chemical bonds) are about 10x stronger than intermolecular

London-Dispersion Forces: He

Dipole-Dipole Forces: HCl

Hydrogen Bonds:

London Dispersion Only Which IM Forces? YES NO Nonpolar Is it polar? Dipole-Dipole London Dispersion Only H-F, H-N or H-O? Hydrogen Bonds Weakest Low BP, MP Stronger Higher BP, MP

Examples: CH4 HF NH3

Warm-up Which type(s) of IM forces are in the following liquids: HCl CO2 CF4 H2O

IMF BP MP IMF BP MP

London Dispersion Forces Another helium nearby, then, would have a dipole induced in it, as the electrons on the left side of helium atom 2 repel the electrons in the cloud on helium atom 1.

London Dispersion Forces London dispersion forces, or dispersion forces, are attractions between an instantaneous dipole and an induced dipole.

London Dispersion Forces These forces are present in all molecules, whether they are polar or nonpolar. The tendency of an electron cloud to distort in this way is called polarizability.

Factors Affecting London Forces The shape of the molecule affects the strength of dispersion forces: long, skinny molecules (like n-pentane tend to have stronger dispersion forces than short, fat ones (like neopentane). This is due to the increased surface area in n-pentane.

Factors Affecting London Forces The strength of dispersion forces tends to increase with increased molecular weight. Larger atoms have larger electron clouds, which are easier to polarize.

Which Have a Greater Effect: Dipole-Dipole Interactions or Dispersion Forces? If two molecules are of comparable size and shape, dipole-dipole interactions will likely be the dominating force. If one molecule is much larger than another, dispersion forces will likely determine its physical properties.

How Do We Explain This? The nonpolar series (SnH4 to CH4) follow the expected trend. The polar series follows the trend from H2Te through H2S, but water is quite an anomaly.

Hydrogen Bonding The dipole-dipole interactions experienced when H is bonded to N, O, or F are unusually strong. We call these interactions hydrogen bonds.

Hydrogen Bonding Hydrogen bonding arises in part from the high electronegativity of nitrogen, oxygen, and fluorine. Also, when hydrogen is bonded to one of those very electronegative elements, the hydrogen nucleus is exposed.

Heating & Cooling Curves Phase Diagrams

Warm-up: Identify the Intermolecular Forces found in the following substances: HCl CO2 NH3 SO3 2. Cl2 is a gas at room temperature, whereas Br2 is a solid. Explain: H2S is a gas at room temperature. Water is much lighter but is a liquid at room temperature. Explain:

Phase Changes

Energy Changes Associated with Changes of State Heat of Fusion: Energy required to change a solid at its melting point to a liquid.

Energy Changes Associated with Changes of State Heat of Vaporization: Energy required to change a liquid at its boiling point to a gas.

Heating/Cooling Curves (Water) T (oC) 0o During a phase change Temperature does not change!!!! Heat Added (kJ)

Energy needed to BOIL: q = nDHVAP Energy needed to MELT: q = nDHFUS Energy needed to HEAT: q = mcpDT During a phase change Temperature does not change!!!!

Energy Changes Associated with Changes of State The heat added to the system at the melting and boiling points goes into pulling the molecules farther apart from each other. The temperature of the substance does not rise during the phase change.

Warm-up:

2. How much energy does it take to melt 1. How much energy does it take to boil 100 g of water? (DHVAP = 41 kJ/mole) 2. How much energy does it take to melt 100 g of water? (DHFUS = 6 kJ/mole)

Heating/Cooling Curve T (oC) 20o Heat Added (kJ)

When water boils are chemical bonds being broken? Explain:

Phase Diagrams The phase of a substance depends on T and P Critical Point Impossible to Liquefy Triple Point

Normal Pressure

What is the phase when T = -90 oC and P = 6 atm? What is T at the triple point? What is the critical temperature? What happens if CO2 at -90 oC and 1 atm is heated at constant P?

Vapor Pressure & Boiling & Freezing Points

What is the phase when T = 20 oC and P = 50 atm? What is P at the triple point? What is the critical temperature? 4. Can liquid CO2 exist above 32oC? 5. What happens if CO2 at -90 oC and 8 atm is heated at constant P?

Vapor Pressure(VP,PVAP): Pressure exerted by a gas above the liquid PVAP depends only on TEMPERATURE!!!!

T VP Weak IMF Strong IMF

When does a substance boil?

Intermolecular Forces IMF BP MP HVAP HFUS VP

Bonding in Solids

Types of Bonding in Crystalline Solids

Bonding in Crystalline Solids Particles arranged in a orderly repeating pattern Molecular: LD, DD, H-bonds- MP varies Ionic: Ions, very strong forces, Lattice Energy (charge, size of ion)-High MP Covalent Network: held together by very strong COVALENT bonds, very high melting points Diamond [C] and Quartz [SiO2] Metallic: Mostly high MP, “Delocalized Electrons)

Ionic Solids: ELat MP MP = 2852oC MP = 801oC

Amorphous Solids

DIAMOND (C) GRAPHITE (C) MP = 3550oC !!!

QUARTZ (SiO2) MP = 1670oC !!!

Metallic Solids Al 660oC Hg -38oC W 3440oC Metals are not covalently bonded, but the attractions between atoms are too strong to be van der Waals forces. In metals, valence electrons are delocalized throughout the solid. Al 660oC Hg -38oC W 3440oC

What IM Forces are in these Solids? CO2 7. C (diamond) H2O 8. NaCl MgO Au SiO2 Ar

Viscosity: measure of resistance to flow

Surface tension: cohesiveness of molecules

Capillary Action: movement of liquids up surfaces Ex) Paper towel in water water up roots

Give examples of : Viscosity in a molecule Capillary action in a molecule Surface Tension in a molecule

“Like-Dissolves-Like” Polar dissolves in polar Nonpolar dissolves in nonpolar Oil = nonpolar Water = polar

Why did the polar bear disappear in water?

Which IMF are in the following: Test Review: Which IMF are in the following: NaCl has a M.P of 801oC and MgO has a M.P. of 2852oC. Why is MgO so much higher. Which would you expect to have a higher BP, F2 or Cl2? What is the vapor pressure of water when it boils? Vapor pressure depends only on ______________ Ar (l) CO2 (s) H2O (l) SiO2 (s) Ag (s) Br2 (l) C (diamond) MgO (s)

Heating/Cooling Curve T (oC) 20o Heat Added (kJ)

Natural Logarithm Calculating Vapor Pressure using Natural Logarithm and the Clausius-Clapeyron Equation (Appendix 1.2)

Wet Dry Ice Lab

What is DRY ICE?

In order to observe liquid CO2 what is the lowest pressure you would need?

Look for the liquid CO2!!!!!!!