intermolecular forces and liquids and solids · intermolecular forces hydrogen bond 11.2 the...

Chemistry for Engineers, SCS126

Intermolecular Forces andLiquids and Solids

Chapter 11


Reading Assignments:

Chapter 11 inR. Chang, Chemistry, 9th Ed., McGraw-Hill, 2006. or previous editions.

Or related topics in other textbooks.

Consultation outside lecture room:Office Hours:

Tuesday & Thursday 10 AM -12 noon, Wednesday 1-4 PM

@Room 313-3 or by appointment


Intermolecular Forces

11.2

molecular forces are attractive forces between molecules.

molecular forces hold atoms together in a molecule.

Intermolecular vs Intramolecular

• 41 kJ to vaporize 1 mole of water (inter)

• 930 kJ to break all O-H bonds in 1 mole of water (intra)

Generally, intermolecular forces are much weaker than intramolecularforces.

“Measure” of intermolecular forceboiling pointmelting point

∆Hvap

∆Hfus

∆Hsub Chemistry for Engineers, SCS126


Dipole-Dipole Forces

Attractive forces between

Orientation of Polar Molecules in a Solid

11.2



Ion-Dipole Forces

Attractive forces between an ion and a polar molecule

11.2 Chemistry for Engineers, SCS126 11.2


Intermolecular ForcesDispersion Forces

Attractive forces that arise as a result of dipoles induced in atoms or molecules

11.2

ion-induced dipole interaction

dipole-induced dipole interaction


Induced Dipoles Interacting With Each Other

11.2


Intermolecular ForcesDispersion Forces Continued

11.2

Polarizability is the ease with which the electron distribution in the atom or molecule can be distorted.

Polarizability increases with:

• greater number of electrons

• more diffuse electron cloud

Dispersion forces usually increase with molar mass.


SO O

What type(s) of intermolecular forces exist between each of the following molecules?

HBr

CH4

SO2

11.2


Intermolecular ForcesHydrogen Bond

11.2

The hydrogen bond is a special dipole-dipole interaction between they hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom.

A H…B A H…Aor

A & B are N, O, or F


Hydrogen Bond

11.2


Why is the hydrogen bond considered a “special” dipole-dipole interaction?

Decreasing molar massDecreasing boiling point

11.2 Chemistry for Engineers, SCS126

Properties of Liquids

Surface tension is the amount of energy required to stretch or increase the surface of a liquid by a unit area.

Strong intermolecular

forces

11.3



Cohesion is the intermolecular attraction between like molecules

11.3

Adhesion is an attraction between unlike molecules



Viscosity is a measure of a fluid’s resistance to flow.

11.3

Strong intermolecular

forces

High viscosity


Maximum Density40C

Ice is less dense than water

Density of Water

11.3

Water is a Unique Substance


A crystalline solid possesses rigid and long-range order. In a crystalline solid, atoms, molecules or ions occupy specific (predictable) positions.An amorphous solid does not possess a well-defined arrangement and long-range molecular order.

A unit cell is the basic repeating structural unit of a crystalline solid.

Unit Cell

latticepoint

Unit cells in 3 dimensions 11.4

At lattice points:

• Atoms

• Molecules

• Ions

Chemistry for Engineers, SCS126 11.4 Chemistry for Engineers, SCS126 11.4

Chemistry for Engineers, SCS126 11.4 Chemistry for Engineers, SCS126 11.4


Shared by 8unit cells

Shared by 2unit cells

11.4 Chemistry for Engineers, SCS126 11.4

1 atom/unit cell(8 x 1/8 = 1)

2 atoms/unit cell(8 x 1/8 + 1 = 2)

4 atoms/unit cell(8 x 1/8 + 6 x 1/2 = 4)

Chemistry for Engineers, SCS126 11.4 Chemistry for Engineers, SCS126

When silver crystallizes, it forms face-centered cubic cells. The unit cell edge length is 409 pm. Calculate the density of silver.

d = mV V = a3

4 atoms/unit cell in a face-centered cubic cell

m = 4 Ag atoms 107.9 gmole Ag

x1 mole Ag

6.022 x 1023 atomsx = 7.17 x 10-22 g

d = mV

7.17 x 10-22 g6.83 x 10-23 cm3=

11.4

Chemistry for Engineers, SCS126 11.5 Chemistry for Engineers, SCS126Extra distance = BC + CD = (Bragg Equation)

11.5


X rays of wavelength 0.154 nm are diffracted from a crystal at an angle of 14.170. Assuming that n = 1, what is the distance (in pm) between layers in the crystal?

nλ = 2d sin θ n = 1 θ = 14.170 λ = 0.154 nm = 154 pm

d =nλ

2sinθ=

1 x 154 pm2 x sin14.17


Types of CrystalsIonic Crystals• Lattice points occupied by cations and anions• Held together by electrostatic attraction• Hard, brittle, high melting point• Poor conductor of heat and electricity

CsCl ZnS CaF211.6


Types of CrystalsCovalent Crystals• Lattice points occupied by atoms• Held together by covalent bonds• Hard, high melting point• Poor conductor of heat and electricity

11.6diamond graphite

carbonatoms


Fullerenes, “Buckyballs”• Buckminsterfullerene ( C60 )

– sp2 hybridized and has bonds to 3 other carbons


Carbon nanotube• Nano wire• Molecular cage


Types of CrystalsMolecular Crystals• Lattice points occupied by molecules• Held together by intermolecular forces• Soft, low melting point• Poor conductor of heat and electricity

11.6


Types of CrystalsMetallic Crystals• Lattice points occupied by metal atoms• Held together by metallic bonds• Soft to hard, low to high melting point• Good conductors of heat and electricity

11.6

Cross Section of a Metallic Crystalnucleus &

inner shell e-

mobile “sea”of e-


Types of Crystals

11.6


An amorphous solid does not possess a well-defined arrangement and long-range molecular order.

A glass is an optically transparent fusion product of inorganic materials that has cooled to a rigid state without crystallizing


Chemistry In Action: High-Temperature Superconductors

intermolecular forces and liquids and solids · intermolecular forces hydrogen bond 11.2 the...

Documents