Chemistry ch 10 notes

Johannes Diderik van der Waals

• His work on the kinetic theory of gases led to further work on connecting liquid and gaseous states

• He received the noble prize for physics in 1910

Van der Waals

• He create a theory describe attractions between molecules

– The theory that describes the electrostatic attraction between molecules is called van der waals forces

We can see his work take place around us in God’s creation today :

• The van der Waals forces can be demonstrated by observing a gecko's climbing ability

• A gecko can hang on a glass surface using only one toe.

• Efforts continue to create a synthetic "gecko tape" that exploits this knowledge.

More on the gecko

Intermolecular forces

• Forces that play an important role in determining the physical properties of various substances

• Classified into three groups– Dipole – dipole– Hydrogen bonds– Dispersion (London) forces

Dipole to dipole interactions

• Remember the polar molecules have unevenly distributed electrical charges

• Positive charges of one molecule attract the negative charge of another molecule the stronger the polarity the stronger the force

• Usually this is a characteristic of ionic molecules – Example: SO2

Hydrogen bonds

• A hydrogen bond is a special type of attractive interaction that exists between an electronegative atom and a hydrogen atom bonded to another electronegative atom.

• This type of bond always involves a hydrogen atom, hence how it gets its name.

Dispersion (London) Forces

• The electrostatic attraction between atoms or molecules that have immediate and generated dipoles– Covalent molecules are said to have

dispersion forces– This force is not just limited to covalent

molecules, however

The three forces

• Dispersion forces work between all kinds of molecules: polar and non-polar.

• Dipole to dipole interactions are only between polar molecules

• Hydrogen bonds only exist between polar molecules that have the correct atoms (hydrogen with nitrogen, hydrogen with oxygen, or hydrogen with fluorine)

Flashback

• describe the behavior of a polar molecule. Is there equal or unequal sharing of electrons?

Sample problem:

• List the types of intermolecular forces that act between the molecules of the following compounds:

• a. O=C=O b. H:F c. Br:Cl• Solution:

__________________________________________________________________________________________________________________

Answers

• A. dispersion, this is a non-polar molecule

• B. all forces are present, hydrogen, dipole-dipole, and dispersion; this molecule is polar

• C. dipole-dipole and dispersion forces, this molecule is polar

Questions?

• Write down 1 question you have so far.

Chart of three forces

• Create your own chart of these three forces on a blank sheet of paper

• Include the force type, description, and example

• cut and paste in your notebook to refer back to later

Example Type Description Example

Dipole to dipole forces

Hydrogen forces

Dispersion forces

Bell work

• Describe one van der waals force:

Determining boiling points

• Things to consider:– Type of bond– Draw the electron dot structure– Count the electron concentrations around the

central atom and determine its shape – Identify the intermolecular forces involved;

dipole to dipole, dispersion, or hydrogen

Turn to page 261

• Table A-1 reveals boiling and melting points of different molecular types

Sample problem

• Using the table 10a-1 on page 261 solve the following

• Which pair has the higher boiling point?

• a. KF or BrF

• B. Cl2 or ICl

Bell work

• Work on the chapter review pg 285 # 2– look on pg 261 table 10A-1

Solids pg 263

• What are some basic properties of solids?

• What is the difference between table salt and carbon tetrachloride? Pg 263

• How does the kinetic theory explain why solids have the properties they do? Pg 263– Give an example:

• Why do solids resist compression?

Two types of solids

• Crystalline solids– Form regular 3 dimensional patterns with

distinct edges and sharp angles– When shattered: smaller shapes form with

similar edges

• Amorphous solids– Have no particular shape– When split or shattered: all kinds of fragments

result

Look on pg 263

• Draw the two patterns on figures 10B-1 and 10 B-2

Creating crystal structures

• Cut and tape shapes together

Bell work

• Draw a solid object

Freezing

• When does a molecule freeze?

• Can a molecule freeze in warm temperatures? Explain. – Salt melts and freezes at temperatures above

800ºC– This is due to its intermolecular forces

between the molecules

Heat • There are two types of heat: sensible and

latent heat

• What is sensible heat? – This type of heat results in a change in

temperature

• Latent heat: when a phase change occurs – the temperature remains constant

• Look on page 264 graphs

Example

• Ice can be heated until it reaches a temperature of zero degrees sensible heat

• The addition of heat at this point will not raise the temperature; it will supply the energy needed for breaking its intermolecular bonds – This is known as latent heat

Differences

• What is the difference between crystal lattice and unit cell – Look on pg 266-267

Answer

• Crystal lattice is a crystals pattern/shape and a crystals unit cell is the smallest part of the crystal

Polymorphs

• Substances that can form more than one type of crystal lattice/pattern

• Allotropic: name give to polymorphous elements

• Allotropes: name give to different forms of allotropic elements – Examples: sulfur, phosphorus, and arsenic

Answer the following in your notes

• What makes strong crystals?

• Explain lattice energy

• Look on pg 269

• Video (diamonds)

• Work on chapter review pg 286 # 12-13

Lab today

• cathedrals

Start working on chapter review

• Pg 286 3-15

Bell work

• Name one crystalline solid shape pg 267

Kinetic description of liquids

• Molecules in liquids are bound together by intermolecular forces that balance out the kinetic energy of the molecule

• Liquid molecules have movement but it is limited unlike gases that have free movement

• They flow and match the shape of the container

Effects of intermolecular attractions

• Surface tension can be demonstrated in liquids such as water, a drop of oil, and a water spider skating across the surface of a pond

• Surface tension is the result of molecules forming an elastic “skin” over the surface of liquids

• The skin forms due to the intermolecular forces of all molecules pointing in the same direction at the surface

Surfactants and Meniscus

• Surfactants– These are detergents known as self-active

agents– They are able to decrease the natural surface

tension

• Meniscus– Is the result of intermolecular attractions

within the liquid as well as between the liquid and the container, the liquid climbs the walls of the container

Capillary rise

• Occurs when the adhesive intermolecular forces between the liquid and a substance are stronger than the cohesive intermolecular forces inside the liquid. – Definition: the movement of a liquid up a narrow tube

caused by the attraction of the molecules in the walls of the tube for the molecules of the liquid

– Capillary action, capillarity, or capillary motion is the ability of a substance to draw another substance into it.

More on capillary rise

• The effect causes a concave meniscus to form where the substance is touching a vertical surface.

• The same effect is what causes porous materials to soak up liquids.

Viscosity

• A liquids ability to resist flowing• This is revealed in how strong the intermolecular

attraction between molecules are• The stronger the attraction the more viscous the

fluid • Temperature affects these forces

– The colder the temperature the more viscous the substance

– The warmer the temperature the less viscous the substance

Problems

• Work on chapter review

pg 287 # 16, 20-21

• Surface tension lab today

Work on problems

• Turn to pg 286 work on 3-15

•

Bell work

• What are surfactants? Given an example of one.

Distillation

• The process of vaporization and condensation

• The process are combined together and are used to separate mixtures

• Describe the difference between critical temperature and critical pressure

Answer

• Critical temperature and critical pressure both bring a gas to its liquid state, critical temperature involves the amount of temperature needed to bring a gas to its liquid state while critical pressure is the pressure exerted on the gas

Specific heat

• The amount of heat required to raise the temperature of one gram of the substance 1 degree Celsius

Sample problem

• What is the boiling point of methanol that is subjected to an atmospheric pressure of 300 torr. Use the graph on page 275 figure 10C-3

• Solution: look across at the vapor pressure of 300 torr (on the side of the graph) find methanol, go straight down and find the temperature in degrees celcius– This is the boiling point

Answer

• 40 degrees Celsius

Sample problem

• If 225 cal of heat energy is added to 50.0 g of water at 25.1°C, what is the final temperature of the water?

Solution

• First determine the temperature change that occurred

• Take 225 cal over 50.0 grams multiply it times the specific heat of water:

• 225 cal x 1.0 g x ºC = 4.50 ºC

50.0g 1.00 cal

Next add 4.5 to the starting temperature, 25.1 ºC = 29.6 ºC ( your answer)

Sample problem

• A 28 g mass of silver is heated from 15ºC to 85ºC. How many joules were added to the sample?

• First determine the rise in temp: 85-15=70ºC• Next use the specific heat determined from table

10C-4 as the conversion factor• Then multiply the specific heat of sliver times

the grams of silver, times the temp change of silver

Solution

• 28 g x 70ºC x 0.23 J = 450J

1.00 g x ºC

↑

from table 10C-4

Questions

• Work on section review 10C

page 285 # 1-3

• When finished: work on crystalline shape cut outs

Bell work

• Answer prelab questions on page 65