LiquidsForces Between Liquid Molecules and their Effect on the Properties of Liquids

Types of ForcesIntramolecular-forces within a molecule-bonding typesexamples: ionic and covalentIntermolecular-forces between moleculesexamples: ionic, dispersion, dipole-dipole, and hydrogen bonding

Ionic ForcesExist between molecules that contain ionic bonds.Result from the electrostatic charges within thecompound.Opposite charges attract.Strongest type of intermolecular force.

London Dispersion ForcesExist between noble gas atoms and nonpolar moleculesWeakestTemporary-as electrons move around the nucleus, a momentary asymmetrical distribution of electrons can occur (provides a temporary dipole)The instantaneous dipole can induce a similar dipole in a neighboring atom

London Dispersion Forces (continued)Large atoms with many electrons have stronger London Dispersion ForcesLarger nonpolar molecules have stronger LD forces

Which has the stronger LD force?Cl2Br2

12345678910111213

Which has the stronger LD force?CH4C2H6C4H10

12345678910111213

Which has the stronger LD force

HeNeArXe

12345678910111213

Dipole-Dipole ForcesExist between polar moleculesPermanentStronger than London Dispersion Forces (1% as strong as ionic/covalent bonds)Created through an unequal sharing of electrons which results in a partial negative and positive chargePositive end of one molecule attracts the negative end of another molecule

Which of the following molecules have dipole-dipole forces present?NH3CH4Both

12345678910111213

Which of the following molecules have dipole-dipole forces?CO2H20Both

12345678910111213

Which of the following molecules have dipole-dipole forces present?SF4SF6Both

12345678910111213

Hydrogen BondingA specific type of dipole-dipole forceOccurs when hydrogen atoms are bonded to highly electronegative atoms such as N, O, or F.Created because of high levels of polarity and small size of hydrogen atoms (especially strong dipole-dipole attraction occurs)

Which of the following compounds has hydrogen bonding present?CH4CH3OHBoth

12345678910111213

Which of the following compounds has hydrogen bonding present?H2SH2OBoth

12345678910111213

Which of the following compounds has hydrogen bonding present?HClHFBoth

12345678910111213

Review of Intermolecular ForcesIdentify the most important type of interparticle forces present in each of the following substances. Ar HCl HF CaCl2 CH4 CO NaNO3

What is the most importance type of interparticle force present in Ar?IonicLondon DispersionDipole-DipoleHydrogen Bonding

123456789101112131415161718192021222324252627282930

What is the most important type of interparticle force present in HCl?IonicLondon DispersionDipole-DipoleHydrogen Bonding

123456789101112131415161718192021222324252627282930

What is the most important type of interparticle force present in HF?IonicLondon DispersionDipole-DipoleHydrogen Bonding

123456789101112131415161718192021222324252627282930

What is the most important type of interparticle force present in CaCl2?IonicLondon DispersionDipole-DipoleHydrogen Bonding

123456789101112131415161718192021222324252627282930

What is the most important type of interparticle force present in CH4?IonicLondon DispersionDipole-DipoleHydrogen Bonding

123456789101112131415161718192021222324252627282930

What is the most important type of interparticle force present in CO?IonicLondon DispersionDipole-DipoleHydrogen Bonding

123456789101112131415161718192021222324252627282930

What is the most important type of interparticle force present in NaNO3?IonicLondon DispersionDipole-DipoleHydrogen Bonding

123456789101112131415161718192021222324252627282930

Arrange the following molecules in order of decreasing intermolecular interaction:SO2, Cl2, CH3OH, CH3NH2CH3OH > CH3NH2>SO2>Cl2Cl2>SO2>CH3OH>CH3NH2SO2>CH3NH2>CH3OH>Cl2CH3NH2>CH3OH>SO2>Cl2

123456789101112131415161718192021222324252627282930

Properties of Liquids

Surface TensionResistance of a liquid to increase in surface areaMeasure of the inward forcesLiquids with high intermolecular forces have high surface tensions

Capillary ActionSpontaneous rising of a liquid in a narrow tubeCaused by cohesive and adhesive forcescohesive forces-intermolecular forces among liquid molecules adhesive forces- force between the liquid molecules and the container; occur when the container is made of a polar substance

Example of Capillary ActionWhen water is placed in a glass graduated cylinder, the meniscus is concaveadhesive forces > cohesive forces (glass is polar)When mercury is placed in the same graduated cylinder, the meniscus is convexcohesive forces > adhesive forces (mercury contains only dispersion forces-nonpolar)

ViscosityA resistance to flowStrong intermolecular forces result in high viscosityLarge molecules also have high viscosity due to greater LD forcesAs temperature increases, viscosity decreases

Vapor PressurePressure of vapor above the surface of a liquidCaused when the molecules on the surface break away and go into the gas phaseIn order to break away, the molecules must possess a minimum amount of kinetic energyHigh intermolecular forces result in low vapor pressuresVolatile liquids are liquids that evaporate rapidly resulting in high vapor pressures

Vapor Pressure (continued)Substances with weak intermolecular forces tend to be volatileAs temperature increases, vapor pressure increases (more molecules possess the minimum kinetic energy and the rate of evaporation increases)See the diagram on page 487.

Calculating Vapor PressureThe equation used to calculate the vapor pressure is: ln (PvapT1) = Hvap(1 - 1) (PvapT2) = R (T2 - T1)

H is the heat of vaporization in J/mol, T is Kelvin temperature, R is 8.314 J/Kmol, and Pvap is vapor pressure

Practice ProblemIn Breckenridge , Colorado, the typical atmospheric pressure is 520. torr. What is the boiling point of water (Hvap = 40.7 kJ/mol) in Breckenridge?

Melting Point and Boiling PointsMelting point- temperature at which the solid and liquid have the same vapor pressureBoiling point-temperature at which the vapor pressure is equal to 1 atm (atmospheric pressure)Melting and boiling points are higher when the intermolecular forces are stronger

Which of the following has the highest boiling point?H2OHFHIHBr

12345678910111213

Which of the following liquids will be the most viscous?C3H8C6H6CH4C2H6

12345678910111213

Arrange the following liquids, A, B, C, with vapor pressures at room temperature of 88, 680, and 155, respectively, in order of decreasing boiling points.B>C>AA>B>CA>C>BC>A>B

12345678910111213

Knowing that solutes with a certain polarity are best dissolved in solutions with similar polarity, which of the following solvents would be optimal for the solvation of CH3COOH?CH4CH3OHC2H6C6H6

12345678910111213