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Kinetic Theory. 1.) All matter is composed of small particles. 2.) These particles are in constant motion. Kinetic Theory. 3.) Collisions between particles are perfectly elastic (no change in total kinetic energy of the system). Physical States. States of Matter Solid Liquid Gaseous

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Kinetic theory
Kinetic Theory

  • 1.) All matter is composed of small particles.

  • 2.) These particles are in constant motion.

Kinetic theory1
Kinetic Theory

  • 3.) Collisions between particles are perfectly elastic (no change in total kinetic energy of the system).

Physical states
Physical States

  • States of Matter

    • Solid

    • Liquid

    • Gaseous

    • Plasma

Liquids solids

  • Molecular Substances:

  • 1.)General Properties- nonconductors of electricity, often insoluble in water, low melting and boiling points.

Molecular substances
Molecular Substances

  • Molecules are relatively easy to separate from each other because intermolecular forces are weak.

Molecular substances1
Molecular Substances

  • 2.) Dispersion Forces - result from temporary dipoles formed in adjacent molecules.

Molecular substances2
Molecular Substances

  • Their strength depends on how readily electrons are dispersed and increase with increasing molecular size and mass.

Molecular substances3
Molecular Substances

  • Ex. Ordinarily the boiling points of molecular substances will increase with increasing molar mass.

Molecular substances4
Molecular Substances

  • Ex. F2 < Cl2 < Br2 < I2.

  • B.P. (in degrees Celsius) are: -188, -34, 59, 184

Molecular substances5
Molecular Substances

  • 3.) Dipole forces- electrical attractive forces between the + end of a polar molecule and the - end of an adjacent molecule.

Kinetic theory

Molecular substances6
Molecular Substances

  • Ex. Compare the boiling pts of NO (bp = -151oC), N2 (bp = -196oC), and O2(bp = - 183oC).

Molecular substances7
Molecular Substances

  • 4.) Hydrogen bonds - are unusually strong dipole forces. The H atom is very small and differs greatly in electronegativity from F, O or N.

Molecular substances8
Molecular Substances

  • Compare the boiling points of Group 16 hydrides -

  • H2O = 100oC

  • H2S = -61oC

  • H2Se = -42oC

  • H2Te = -2oC

Molecular substances9
Molecular Substances

  • Note that water has many unusual properties in addition to high boiling point. The open structure of ice, a result of hydrogen bonding, accounts for its low density.

Nonmolecular solids
Nonmolecular Solids

  • Network Covalent Solids - ex. C, SiC, SiO2 (see. P. 246, 247)

    • High melting pts (covalent bonds must be broken)

    • Nonconducting

    • Insoluble in water and other common solvents.

Nonmolecular solids1
Nonmolecular Solids

  • Network Covalent Solids- ex. Compare the properties of diamond and graphite (allotropes)

Nonmolecular solids2
Nonmolecular Solids

  • Ionic Solids- ex. NaCl, KNO3

    • High melting points (due to strong attractive forces between oppositely charged ions).

Nonmolecular solids3
Nonmolecular Solids

  • Ionic Solids-

    • Nonconducting as solids, conducting when molten

    • Often water soluble (depends on between attractive forces for each other versus for water)

Nonmolecular solids4
Nonmolecular Solids

  • Ionic Bond Strength-

    • Remember Coulomb’s Law - ex. CaO melts at 2927oC vs NaCl at 801oC

    • Ex NaCl slightly higher than KBr (internuclear distance)

Nonmolecular solids5
Nonmolecular Solids

  • Metallic Crystal/Solids-

    • “Electron-sea” model (d-orbital overlap); cations in mobile sea of electrons.

    • Conduct electricity, heat

Nonmolecular solids6
Nonmolecular Solids

  • Metallic Crystal/Solids-

    • Electrical conductivity is enhanced by the mobility of electrons

    • Heat is carried by the collision of electrons (which is frequent in metals)

Nonmolecular solids7
Nonmolecular Solids

  • Metallic Crystal/Solids-

    • Ductile, maleable.

    • Wide range of melting points, depending on the number of valence electrons.

Nonmolecular solids8
Nonmolecular Solids

  • Metallic Crystal/Solids-

    • Electrons act as a flexible glue holding the atomic nuclei together

    • Lowest melting pt from +1 cations

Nonmolecular solids9
Nonmolecular Solids

  • Metallic Crystal/Solids-

    • Insoluble in water and other common solvents

    • Cations cannot dissolve by themselves

Crystal structures
Crystal Structures

  • Unit Cells in Metals-

    • Unit Cell: smallest unit which, repeated over and over again, generates the crystal.

Crystal structures1
Crystal Structures

  • Simple Cubic - unit cell consists of eight atoms at the corners of a cube.

  • 2r = s

  • r = atomic radius, s = edge length

Crystal structures2
Crystal Structures

  • Face centered cubic - atoms at the corners of a cube and in the center of each face. Atoms touch along the face diagonally.

  • 4r = s(2)1/2

Crystal structures3
Crystal Structures

  • Body-centered cubic: atoms at corner of cube and at center. Atoms touch along the body diagonally.

    • 4r = s(3)1/2

Crystal structure
Crystal Structure

Sodium crystallizes into a BCC structure; the unit cell has a length of 0.429nm. What is the atomic radius?

r = s(3)1/2/4 = 0.186nm

Liq vap equilibria
Liq-Vap Equilibria

  • Vapor Pressure - when a liquid is introduced into a closed container, it establishes a dynamic equilibrium with its vapor.

  • Liquid <--> vapor

Liq vap equilibria1
Liq-Vap Equilibria

  • The pressure of the vapor at equilibrium is referred to as the vapor pressure of the liquid.

Liq vap equilibria2
Liq-Vap Equilibria

  • Vapor Pressure is independent of the volume of the container.

Liq vap equilibria3
Liq-Vap Equilibria

  • Add 0.0100 mol of liquid benzene to 1.00L flask at 25oC (vp benzene = 92 mm Hg). How much of the benzene vaporizes?

  • n vap = 0.0050 mol, n liq = 0.0050 mol

Liq vap equilibria4
Liq-Vap Equilibria

  • Add 0.0100 mol of liquid benzene to 2.00L flask at 25oC (vp benzene = 92 mm Hg). How much of the benzene vaporizes?

  • all; no equilibrium is established

Liq vap equilibria5
Liq-Vap Equilibria

  • Temperature dependence of vapor pressure: the vapor pressure of a liquid is always increases as temperature does.

Kinetic theory

Vapor pressure



(degrees C)

Log VP vs

1/T (K)

Liq vap equilibria6
Liq-Vap Equilibria

  • Water evaporates most readily on hot, dry days.

  • Stoppers pop out of bottle of volatile liquids as temperature rises.

Liq vap equilibria7
Liq-Vap Equilibria

  • (to get a linear relationship) Use the Clausius-Clapeyron equation:

  • ln P2/P1 = Hvap (1/T1 - 1/T2)/R

  • Hvap = heat of vaporization in joules per mole

  • R = 8.31 J/mol*K

Liq vap equilibria8
Liq-Vap Equilibria

  • Vapor pressure of water:

Liq vap equilibria9
Liq-Vap Equilibria

Take the heat of vaporization of benzene to be 30.8 kJ/mol, vp benzene at 25oC = 92 mm Hg. What is the vapor pressure of benzene at 50oC?

241 mm Hg

Liq vap equilibria10
Liq-Vap Equilibria

  • NOTE: the pressure more than doubles when T rises from 25 to 50oC, reflecting the fact that more benzene vaporizes.

  • The pressure of an ideal gas only increases by 10%.

Liq vap equilibria11
Liq-Vap Equilibria

  • Boiling Point = temperature at which vapor bubbles form in liquid. Hence, boiling point varies with applied pressure.

  • When the pressure is 760 mm Hg, water boils at 100oC, at 1075 mm Hg, it boils at 110oC, at 5 mm Hg, it boils at 0oC.

Kinetic theory



Liq vap equilibria12
Liq-Vap Equilibria

  • Critical temperature: temperature above which liquid cannot exist.

  • Critical pressure: vapor pressure at critical T.

Liq vap equilibria13
Liq-Vap Equilibria

  • Ex. Since critical T of oxygen is -119oC, liquid oxygen cannot exist at room temperature, regardless of pressure.

  • Critical T of propane is 97oC; propane is stored as a liquid under pressure at room T.

Phase diagrams
Phase Diagrams

  • Phase diagram - a graph showing temperatures and pressures at which liquid, solid, and vapor phases of a substance can exist.

Kinetic theory





Phase diagrams1
Phase Diagrams

  • AB = vp curve, liquid - b p line

  • AC = vp curve, solid - sublimation

  • AD = melting point line

  • A = triple point

  • B = normal BP

Phase diagrams2
Phase Diagrams

  • If AD slopes toward the P axis, mp decreases as P increases. This is true for water, where the liquid is the denser phase.

  • More often the solid is denser. AD slopes away from P axis & mp increases with pressure.

Kinetic theory

Liquid more dense

- water

Solid more dense

Liq vap equilibria14
Liq-Vap Equilibria

  • NOTE: solid sublimes below the triple point

  • If the line AD slopes toward P axis, melting point decreases as P increases. This behavior is observed for water, where the liquid is the more dense phase. More often, AD tilts away from the P axis, and the melting point increases with pressure.