intermolecular forces: liquids, and solids -...

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Intermolecular Forces:

Liquids, and Solids

Chapter 11

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Review Practice

Excited Na atoms may emit radiation having a wavelength of 589 nm.

a) What is the wavelength in meters?

b) What is the frequency of this light?

c) What region of the spectrum is this in?

d) What is the energy of this light?

A radio station has a frequency of 96.5 MHz. Find the wavelength and

E.

Microwaves have a frequency of around 2.5 GHz. What is the

wavelength? (1 GHz = 109 Hz)

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Review Practice What is the energy associated with 688 nm light? What

color light is this?

A certain photon of radiation has energy of 4.65 x 10-15 J. What is the wavelength of this light, in nm?

A certain light has an energy of 4.56 x 10-19 J. What color is this light? (Hint: find wavelength in nm.)

The density of NO2 gas at STP is…

Reading Strategies for Free

Response questions

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The Five Analytical Moves

1. Suspend Your Judgment

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Try not to jump to conclusions and evaluate what

is being asked without knowing all the parts.

Ex. What is the molecular geometry of XeF4?

I hope you did not guess tetrahedral because you see

four(4) atoms around the central

2. Define significant parts and how

they are related

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Identify what is needed to find the solution to the

questions.

What are all of the pieces

Are there any special rules of circumstances I

should remember

Ex. What is the molecular geometry of XeF4?

What are the pieces:

Are there any special rules of circumstances I

should remember:

6 e- domains: 4 bonding and 2 none

bonding

Violation of octet rule allowed because

Xe is high than 3d

3. Look for patterns of repetition and

contrast and for anomaly

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Are there any key words that might be a hint to go

in a specific direction?

Are the examples extremely familiar to you because

they were used in your text or in class

4. Make the Implicit Explicit

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Explicit (overtly stated)

Implicit (suggested but not directly stated)

Process of converting suggestions into direct statements is ESSENTIAL to analysis.

Looking for key words that will help you in decision making of how to solve a problem.

Steps, justify, analyze, explain, etc.

5. Keep reformulating questions and

explanations

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What details/ data seem significant? Why?

• What does the detail/data mean?

• What else might it mean?

How do the details/ data fit together? What do they have in common?

What details do not fit? How might they be connected with other details to form a different pattern?

Fortunately most if not all free response questions will be strait forward a VERY clear.

Lets Try One

Expectations:

At each part of the questions you will go

through steps 1-5 AND incorporate them with

the problem solving method we use in here –

time should not be a factor right now.

Remember keep your answers to the point

and simple.

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2008 AP Free Response Question:

Part A question2 Answer the following questions relating to

gravimetric analysis. In the first of two

experiments, a student is assigned the task of

determining the number of moles of water in

one mole of MgCl2 ⋅ n H2O. The student collects

the data shown in the following table.

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Mass of empty container 22.347 g

Initial mass of sample and container 25.825 g

Mass of sample and container after first heating 23.982 g

Mass of sample and container after second heating 23.976 g

Mass of sample and container after third heating 23.977 g

2008 AP Free Response Question

(a) Explain why the student can correctly conclude that

the hydrate was heated a sufficient number of times

in the experiment.

(b) Use the data above to

(i) calculate the total number of moles of water lost

when the sample was heated, and

(ii) determine the formula of the hydrated

compound.

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(c) A different student heats the hydrate in an

uncovered crucible, and some of the solid spatters

out of the crucible. This spattering will have what

effect on the calculated mass of the water lost by the

hydrate?

Justify your answer.

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In the second experiment, a student is given 2.94 g of a

mixture containing anhydrous MgCl2 and KNO3 . To

determine the percentage by mass of MgCl2 in the

mixture, the student uses excess AgNO3 (aq) to

precipitate the chloride ion as AgCl(s).

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(d) Starting with the 2.94 g sample of the mixture

dissolved in water, briefly describe the steps

necessary to quantitatively determine the mass of the

AgCl precipitate.

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(e) The student determines the mass of the AgCl

precipitate to be 5.48 g. On the basis of this

information, calculate each of the following.

(i) The number of moles of MgCl2 in the original

mixture

(ii) The percent by mass of MgCl2 in the original

mixture

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A Molecular Comparison of Liquids and

Solids

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Intermolecular Forces

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Ion-Dipole Forces

- Interaction between an ion (Na+)

and a dipole (water).

- Strongest of all intermolecular

forces

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Na+, Cl- and H2O

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Dipole-Dipole Forces

- Interaction between a _______ on

one molecule and a ________ on an

adjacent molecule.

- ________ forces exist between

neutral polar molecules.

- Weaker than ion-dipole forces

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Intermolecular Forces London Dispersion Forces

Induced Dipole – Induced Dipole

- _________ of all intermolecular forces.

- It is possible for two adjacent nonpolar

molecules to affect each other.

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London Dispersion Forces Induced Dipole – Induced Dipole

- The nucleus of one molecule (or atom)

_____________of the adjacent molecule

(or atom).

- This attraction causes the electron clouds

become distorted.

- In that instant a polar molecule (_____)

is formed (called an instantaneous

dipole).

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London Dispersion Forces

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Hydrogen Bonding

- A special case of dipole-dipole forces.

- This intermolecular force is very strong.

- ___________ of the three Van der

Waal’s forces (Hydrogen bonding,

Dipole-dipole, London forces,)

- H-bonding requires H bonded to an

electronegative element (most important

for compounds of F, O, and N).

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Hydrogen Bonding

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Some Properties of Liquids

Viscosity

- Viscosity

- A liquid flows by sliding molecules over

each other.

- The stronger the intermolecular forces,

the _________ the viscosity.

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Surface Tension

- The surface of a liquid behaves as a

____________________________.

- This is due to the unequal attractive

forces on molecules at the surface.

- Surface molecules are only attracted

_________ towards the bulk molecules.

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Surface Tension

- Cohesive forces

- Adhesive forces

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Surface Tension

- Meniscus is the shape of the liquid surface.

– If adhesive forces are greater than cohesive

forces, the liquid surface is __________to its

container more than the bulk molecules.

Therefore, the meniscus is U-shaped (e.g.

water in glass).

– If cohesive forces are greater than adhesive

forces, the meniscus is curved downwards.

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Surface Tension

________________- When a narrow glass tube is

placed in water, the meniscus pulls the water

up the tube.

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.

Recall

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Properties of Liquids Vaporization

Also called evaporation

– _

Standard molar enthalpy of vaporization (DHovap)

The resulting gas will exert a pressure on a

system.

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Properties of Liquids Vapor Pressure

• This is the pressure exerted by a substance in

the gas phase.

• As a liquid’s temperature increases, its vapor

pressure increases.

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Properties of Liquids

Vapor Pressure

Volatile –

Or

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Vapor Pressure and Boiling Point

- Liquids boil when the external pressure

_______ the vapor pressure.

- Two ways to get a liquid to boil: _______

temperature or __________ pressure.

- Normal boiling point is the boiling point

at 760 mmHg (1 atm).

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Try to draw a picture representing the gas

and liquid molecules and what they are

doing during boiling of a liquid.

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- Vapor pressure, temperature and

enthalpy of vaporization can be related

to each other using:

Clausius-Clapeyron equation:

D

211

2 11ln

TTR

H

P

Po

vapP = __________

T = ___________

R = _____________

DHovap = ___________________

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The Clausius-Clapeyron equation makes

more sense when it is rearranged into the

slope intercept form.

CRT

HP

o

vap

Dln

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Structures of Solids Unit Cells

- Crystalline solid: well-ordered, definite

arrangements of molecules, atoms or ions.

- Crystals have an ordered, repeated

structure.

- The smallest repeating unit in a crystal is a

________.

- Three-dimensional stacking of unit cells is

the crystal lattice.

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Review

Name the intermolecular forces that must

be overcome to convert each of the

following from a liquid to a gas:

a) Br2; b) CH3OH; c) H2S

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Structures of Solids

Unit Cells

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Unit Cells

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Cell Occupancy

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Cell Occupancy

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Cell Occupancy

Site Occupancy

Corner 1/8

Edge 1/4

Face 1/2

Center 1

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Cell Occupancy

Zinc (grey) 4 Center 4 atoms

Sulfur (yellow) 8 corners

6 faces

1 atom

3 atoms

Zn4S4 ZnS

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Close Packing of Spheres

- A crystal is built up by placing close

packed layers of spheres on top of each

other.

- There is only one place for the second

layer of spheres.

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Structures of Solids Close Packing of Spheres

- There are two choices for the third layer

of spheres:

- Third layer eclipses the first (ABAB

arrangement). This is called hexagonal

close packing (hcp).

- Third layer is in a different position

relative to the first (ABCABC

arrangement). This is called cubic close

packing (ccp).

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- Each sphere is surrounded by 12 other

spheres (6 in one plane, 3 above and 3

below).

- Coordination number: the number of

spheres directly surrounding a central

sphere.

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Other Kinds of Solid Materials

Molecular Solids

These are crystalline substances in

which the “building blocks” are

composed of molecules in place of

ions.

Example: Table Sugar

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Other Kinds of Solid Materials

Network Solids

These are crystalline substances in which

the “building blocks” are atoms and all

the atoms are connected by covalent

bonds.

Example: Diamond

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Phase Diagrams

Phase diagram: plot of pressure vs.

temperature summarizing all equilibria

between phases.

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Phase Diagrams

Triple point - Temperature and

pressure at which all three phases

are in equilibrium.

Critical point – Point above which

the liquid and gas phases are

indistinguishable.

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Phase Diagrams

Critical temperature - The minimum

temperature for liquefaction of a gas

using pressure

Critical pressure -

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Ch. 11:

11, 13, 15, 19, 23, 27, 29, 33, 39, 47, 55, 69, 76

Homework

intermolecular forces: liquids, and solids -...

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