intermolecular forces
DESCRIPTION
Intermolecular Forces. Intermolecular Forces. Van der Waals Forces—the two weakest attractions between molecules. Dipole interaction—polar molecules are attracted to one another (kind of like magnets). Intermolecular Forces. Van der Waals Forces—the two weakest attractions between molecules. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/1.jpg)
Intermolecular Forces
![Page 2: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/2.jpg)
Intermolecular Forces• Van der Waals Forces—the two weakest
attractions between molecules.– Dipole interaction—polar molecules are
attracted to one another (kind of like magnets)
![Page 3: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/3.jpg)
Intermolecular Forces• Van der Waals Forces—the two weakest attractions
between molecules.– Dispersion forces—when an atom’s electrons are
concentrated in one place, it causes its neighbor’s electrons to move
![Page 4: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/4.jpg)
Intermolecular Forces• Hydrogen Bonding—when hydrogen is bonded
to an electronegative atom(O,N,F), it creates polarity. This polarity creates an attraction between molecules. Much stronger than the other two, but NOT a true bond.
![Page 5: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/5.jpg)
Kinetic Molecular Theory (KMT)• Solid, liquid or gas, the particles that
make up matter are in constant motion.
• Particles in a liquid or a solid are attracted to each other.
![Page 6: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/6.jpg)
Liquids• The disruptive motion of particles
of a liquid versus the attractive forces between them causes the liquid to flow and have volume.
![Page 7: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/7.jpg)
All liquids possess the following:
• Vapor Pressure• Boiling Point• Viscosity• Surface Tension• The amount of each that a liquid
possesses is due to the attractive forces between the particles of that liquid.
![Page 8: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/8.jpg)
Vapor Pressure• Vaporization-conversion of a liquid to a gas.• Evaporation is the conversion to a gas at the
surface of a liquid (NOT boiling).DEMO
• Vapor pressure is the pressure caused by the evaporated particles above the surface of a liquid.
![Page 9: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/9.jpg)
Atmospheric Pressure
• The air is ~7 miles high.
• That air piled upon you exerts a pressure.
• That pressure is 14.7 lb/in2
![Page 10: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/10.jpg)
Atmospheric Pressure
• This air pressure has a HUGE effect on what things on this planet look like and how they work.
![Page 11: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/11.jpg)
Would These Things Work the Same At Zero Atmospheric
Pressure?suction cup parachute drinking straw
candle pogo stick broom
match swing alarm clock
flashlight automobile shotgun
vacuum cleaner air bag radio
paper airplane balloon bow and arrow
helicopter paint star
rocket blow dryer bicycle pump
aerosol spray can Frisbee flag
baseball and bat TNT golf
plant siphon refrigerator
syringe smoke detector magnet
![Page 12: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/12.jpg)
Boiling Point• When a liquid is heated enough (at a particular
atmospheric pressure), particles everywhere in the liquid start to vaporize. This is the boiling point of that liquid.
• At this point, vapor pressure = atmospheric pressure. DEMO
• Every pure liquid has its own bp.
![Page 13: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/13.jpg)
Viscosity• Resistance to flow.DEMO
• Again, every pure liquid has its own.
![Page 14: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/14.jpg)
Surface Tension• Results from an imbalance of
attraction between liquid particles at the surface of the liquid.
• Liquid acts as if it has a skin.
![Page 15: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/15.jpg)
Surface Tension
• Allows things like this:
![Page 16: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/16.jpg)
Water• As a result of water’s polarity, it
exhibits hydrogen bonding.
• Hydrogen bonding is the cause of almost all of water’s unique and important properties.
![Page 17: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/17.jpg)
Hydrogen Bonding in Water• Gives water a high surface tension.DEMO
• Give it a low vapor pressure/high boiling point.• Make it denser as a liquid than as a solid.DEMO
![Page 18: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/18.jpg)
• #1. Using the rule of LIKE DISSOLVES LIKE, which of the following left outside would get dissolved by rain and end up in your well water.
• Candle waxSugarSalt (sodium chloride)Drywall (CaSO4) (hint Ca=+2 charge, SO4=-2 charge)Lead ChlorideSodium FluoridePlastic bottlesGlass bottlesAlcohol
![Page 19: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/19.jpg)
#2: Soap is made from a chain of carbon and hydrogen atoms (zig-zag line) connected to a
charged group of atoms like SO4. The chains of carbons have no charge so they are ignored by
water as they migrate through the water
![Page 20: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/20.jpg)
The oil in the oil droplet has no charge and blends nicely with the long carbon chain end of
soap, which also has no charge. The water molecules, however, are attracted to the charged
end of the soap molecule.
![Page 21: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/21.jpg)
Eventually, the soap molecules will align themselves so the non-charged end will stay dissolved in the oil drop, but the charged SO4 end well be held on to by water.
Instead of the oil drop getting squeezed out of the way of water, it gets attracted by water because it has these
charged SO4 groups sticking out of it. So in essence, the soap allows water to dissolve oil. Question: Is the plus or
negative side of water attracted to the SO4 groups?
![Page 22: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/22.jpg)
3. Since water has a partially charged plus and minus ends, it aligns itself like a crosslinked net (or skin) at the surface of water. They call this
surface tension. Mosquito larva take advantage of the strength of surface tension by suspending
themselves from the water's surface.
![Page 23: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/23.jpg)
This represents what water molecules would do at the surface. They line up + to -, which gives it
strength. However, if soap is added to the water...
![Page 24: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/24.jpg)
...the alignment of water is disrupted. This soap molecule has a chain of carbons and hydrogens that water ignores, and a
negatively charged SO4 group that attracts the positive end of water molecules. This disrupts the previous chain of water
molecules (the net) but the water still locks onto the negative SO4 group. The long chain of carbons and hydrogens have no charge
so water is not attracted to these chains. This weakens the
surface tension. Why?
![Page 25: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/25.jpg)
Soap added to water causes the mosquito larvae to sink thereby dooming the adult mosquito from
ever making it to the air. As this remarkable picture shows, with water surface tension intact,
the adult mosquito can escape into the air.
![Page 26: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/26.jpg)
Solids• If the particles of all liquids are
attracted to each other, then the particles of solids are even more so.
• Particles of most solids are closely & orderly packed and have vibration as their only form of motion.
![Page 27: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/27.jpg)
Amorphous Solids
• Some solids, when they form, do not have their particles in an orderly arrangement. These are called amorphous solids.
• Examples: rubber, glass
![Page 28: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/28.jpg)
Motion of Particles
• The particles of a substance have three types of motion, depending on the phase they are in:
–Translational
–Rotational
–Vibrational
![Page 29: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/29.jpg)
Phase Diagrams• A phase diagram lets you work out exactly what
phases are present at any given temperature and pressure.
• Here is the phase diagram for water:
![Page 30: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/30.jpg)
![Page 31: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/31.jpg)
Here’s one for CO2:
![Page 32: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/32.jpg)
Heating Curves• The graph of temperature against time is called a heating
curve. Here’s one for water:
Notice that, in general, the temperature goes up the longer the heating continues. However, there are two horizontal flat parts to the graph. These happen when there is a change of state.
![Page 33: Intermolecular Forces](https://reader035.vdocuments.net/reader035/viewer/2022062422/56813af7550346895da37e9a/html5/thumbnails/33.jpg)
• Here is a heating curve for iron:
• At what temp. does iron melt?• At what temp. does iron boil?• These heating curves are accurate,
assuming what state of conditions?