IMFs Lesson Plan
Name: Sara Adamek
Class/Subject: AP Prep Chemistry
Date: May 5-9, 2014
Student Objectives/Student Outcomes:
Objectives
Assessment
Students will be able to
Molecular drawings will show clear differences between the density,
draw on a molecular
organization, and speed of the molecules that make up each substance.
level solids liquids and
gases.
Students will be able to
London-Dispersion: Because the electrons are moving around occasionally
describe the three types
they are not evenly distributed around the atom or molecule. This causes a
of intermolecular forces. temporary dipole (areas of neg and positive charge) which infludences other
molecules to create their own temporary dipole. This causes the molecules to
stick together like socks out of the dryer. This is the weakest IMF.
Dipole-dipole: These IMFs are caused by electronegativity differences. The
more electronegative atom ‘steals’ the electons from the less electronegative
atom. This causes one area of the molecule to be more negative and another
to be more positive. This causes the molecules to line up positive to negative
parts and sort of stick together. This force is stronger than London dispersion.
Hydergen bonds: These bonds only exist between H and O, N or F. Because
hydrogen is essentially a positive nucleus when bonded to the extremely
electronegative O, N or F it creates a very strong dipole. This is the strongest
of the IMFS.
Students will be able to
Ex. Water has a higher boiling point than other similar compounds because it
explain physical
has two hydrogen bonds. The oxygen is so electronegative that the electrons
characteristics with
spend most of their time around the oxygen. This leaves a ‘naked’ nucleus
reference to IMFs.
which is positive by itself. This means that there is a strongly negative and
two strongly positive ends to each water molecule. The positive ends of one
molecule are attracted to the negative ends of another. This positive-negative
attraction causes water molecules to stick together more than other similar
compounds. This means that more energy has to be put into the water to
break the hydrogen bonds.
Content Standards:
HS-PS1 Matter and its Interactions
Students who demonstrate understanding can:
HS-PS1-1.
Use the periodic table as a model to predict the relative properties of
elements based on the patterns of electrons in the outermost energy
level of atoms
HS-PS1-3.
Plan and conduct an investigation to gather evidence to compare the
structure of substances at the bulk scale to infer the strength of electrical
forces between particles.
Materials/Resources/Technology:
-Ppt, white boards, markers, erasers
Time (Review game for heat)
Start of Class:
Collect POGIL and other hw. Take attendance.
Introduction of Lesson:
Place students in groups. Pass out white boards, markers and erasers.
Lesson Instruction:
Present ppt. discuss as we go along. Keep track of points.
Assessment/Checks for understanding:
Informal as we go along.
Closure/Wrap-up/Review:
Remind students of quiz tomorrow. Have extra review sheets to pass out.
Materials/Resources/Technology:
Heat quiz and IMF POGIL
Time ( Heat quiz and IMF POGIL)
Start of Class:
Take attendance Pass back papers
Introduction of Lesson:
Ask for last min. questions. Give students ten minutes to study/ask questions/review
corrected HW. Have students put away their things.
Lesson Instruction:
Pass out quizzes. When the quizzes are finished pick up the POGIL and work on it.
Assessment/Checks for understanding:
Grade quiz for accuracy. Grade POGIL for completion, give feedback.
Closure/Wrap-up/Review:
IF there is time review major ideas of the POGIL.
Materials/Resources/Technology:
-POGIL packet
Time (IMF POGIL)
Start of Class:
Pass pack POGIL first part. Take attendance.
Introduction of Lesson:
Review Part one of POGIL. Focus on drawing molecules/atoms.
Lesson Instruction:
Give students time to work on part 2 of the POGIL.
Assessment/Checks for understanding:
Check POGIL for completion, provide feedback.
Closure/Wrap-up/Review:
Review Dispersion, dipole-dipole, and hydrogen bonding.
Materials/Resources/Technology:
Time (liquid nitrogen ice cream)
-sugar, milk, ½ & ½, vanilla, bowl, cups, spoons, wooden spoon, flowers, liquid nitrogen, racquet balls
Start of Class:
Take attendance
Introduction of Lesson:
Have students get out POGIL. Discuss. Emphasize electronegativity.
Lesson Instruction:
Review heat with students. Heat flows from hot to cool. Porperties of matter change based
on temperature. Molecules slow down when they cool down. Substances can have phase
changes based on temperature.
Demo freezing/shattering a flower, shattering a racquet ball. Make icecream.
Assessment/Checks for understanding:
Informal assessment, check POGIL for completion, provide feedback.
Closure/Wrap-up/Review:
Materials/Resources/Technology:
-IMFs cards and wks
Time
Start of Class:
Take attendance. Pass back papers
Introduction of Lesson:
Have students get out POGIL. Finish discussing. Emphasize electronegativity.
Lesson Instruction:
Review hydrogen bonding, dipole-dipole, dispersion forces.
Pass out IMF worksheet. Group students in pairs. Pass out IMF cards.
Release students to do the activity.
Collect worksheets at the end of the hour.
If there is time, have students write about the properties of water, methanol and methane.
Assessment/Checks for understanding:
Check POGIL for completion, provide feedback. Provide feedback for writing.
Closure/Wrap-up/Review:
Have students share some of their answers from the IMF wks.
Methane CH
Ethane C H
4
2
Water H O
Propane C H
6
3
8
Bromobenzene C H Br
2
6
Nitrogen N
5
Carbon monoxide CO
2
Fluorine F
2
Methanol CH OH
3
Propanone C H O
3
Hydrogen fluoride HF
6
Carbon dioxide CO
2
INTERMOLECULAR FORCES
Name:______________
1. Take the cards out of the envelope and arrange them in four groups based on the number on the
back of the card. Ex: Group 1 should have hydrogen fluoride, propanone and carbon dioxide in it.
2. Arrange the cards in their groups from least strong IMFs to most strong.
3. Do you notice any patterns? Describe two you see. Use complete sentences.
4. Record the order of the cards in group 1 here.
5. What type(s) of IMFs are found in the group? ________________________________________
a. Describe how hydrogen bonds work.
b. Describe how dipole-dipole bonds work.
c. Describe how dispersion forces work.
6. Which molecule would have the highest boiling point? _________________________________
7. Which molecule would have the lowest boiling point? __________________________________
8. How did you know the answers to # 5 and 6? Use complete sentences.
9. Record the order of the cards in group 2 here.
10. Assume all of the molecules are in their liquid state. Arrange them in order from least amount of
surface tension to most amount of surface tension.
11. Record the order of the cards in group 3 here.
12. Explain which state you would expect the molecules in group 3 to be in at room temperature.
EXPLAIN your reasoning.
a. Water
b. Bromobenzene
c. Nitrogen
13. Record the order of the cards in group 4 here.
14. What type(s) of intermolecular forces are in group 4? __________________________________
15. What influences the strength of these types of IMFs? ___________________________________
16. Given the information below, answer the following questions.
Molecule
Propane
Ethane
Methane
Methanol
Carbon dioxide
Water
Boiling point (°C)
-42
-89
-164
64.7
-57
100
a. Why is the boiling point of carbon dioxide so much less than the boiling point of water?
b. Why is the boiling point of water so much higher than the boiling point of methanol?
c. Arrange propane, methane and ethane in order of least vapor pressure to highest vapor
pressure. Remember vapor pressure is the pressure that comes from molecules that have left
the liquid state and gone into the gas state.
POGIL for states of matter
Part I:
Name: __________________
States of Matter – what atoms and molecules are doing
Purpose: Learn to draw what is happening in solids, liquids and gases.
First, we should review the anatomy of an atom. Remember that atoms have protons and
neutrons in the nucleus. They also have electrons floating around outside of the nucleus. Each of
these particles has a unique charge.
1. What are those charges?
2. Please draw an atom of lithium here.
Solids: A solid is a material that has a definite shape and definite volume. The density of a solid is usually
high – greater than 1.0 gram/mL. Because of the fixed shape, we can imagine that the molecules of the solid
are not able to move around. By other types of measurements, we find out that the molecules are just
vibrating back and forth in a fixed position.
3. Based on the high density of a solid, how do you think the molecules are arranged in a solid? Write
something about how far apart they are from each other, and how they are arranged.
Usually when we draw atoms we imagine them as spheres that contain the nucleus and any electrons the
atoms have. This is a model and it is simplified from reality but it allows us to think about and show the
interactions between atoms without getting caught up in the details.
4. Draw the molecules in a small part of a solid. Show how close they are from each other, whether they
have an organized arrangement or not, and how they are moving.
Liquids: A liquid has a definite volume, but no definite shape. The density of a liquid is
also high, around 1.0 grams/mL. Because their shape is not fixed, we can imagine the
molecules being able to move around. Liquids can be poured into a new container. We
can do experiments to measure the speed of a molecule in a liquid, by observing how food
coloring travels.
5.
Based on the high density of a liquid, how do you think the molecules are arranged in a liquid? Write
something about how far apart they are from each other, and how they are arranged.
6. Draw the molecules in a small part of a liquid. Show how close they are from each other, whether they
have an organized arrangement or not, and how they are moving.
Gases: A gas does not have a definite volume, or a definite shape. The density of a gas is
very low, less than about 0.1 grams/mL. Because their shape is not fixed, we can imagine
the molecules being able to move around. Gases have another property that liquids do not
– they expand to fill their container. We can do experiments to measure the speed of a
molecule in a gas, by observing how room spray or perfume travels.
7.
Based on the low density of a gas, how do you think the molecules are arranged in
a gas? Write something about how far apart they are from each other, and how
they are arranged.
8. Write something else you know about a gas, based on personal experience. Write about the
observations you have made.
9. Draw the molecules in a small part of a gas. Show how close they are from each other, whether they
have an organized arrangement or not, and how they are moving.
Part II. Forces holding matter together.
Name:______________
You may have asked the question – why are some things gases, others liquids, and others solids? There
are some simple explanations for this, based on the idea of molecules having charge.
Remember that opposite charges (+ and -) attract each other. If a particle of a solid has a (+) charge, and
its neighbor has a (-) charge, they will attract each other.
Now think about ionic compounds. In an ionic compound such as NaCl, there are electrons stolen from
the sodium by the chlorine, so that each sodium is Na+1 and each chlorine is Cl –1. These have a very
strong attraction for each other.
10. Thinking about salt (NaCl), is it normally a solid, liquid or gas? _________________________
11. Thinking about the charges and the attraction between Na+1 and Cl –1, do you think the atoms
can move? Why or why not?
12. As a general answer, do you think ionic substances are solids, liquids or gases?
So we can propose that ionic substances have atoms locked in place because they form a grid of
negative and positive charges that hold the individual atoms in place. But not everything is ionic, there
are many, many covalent compounds. (Remember a covalent compound is formed by two or more non
metals.) Why are some of them gases, some liquids and some solids?
Ans: It depends on how strongly the molecules are held together. We will look at three types of forces.
These are all called intermolecular forces because they are between molecules. They are based on the
weak charges that exist in molecules. NOTE: these are all much weaker than ionic bonds.
A. Some molecules are held together by fairly strong, but still weaker than ionic, forces. These
molecules have a Hydrogen atom attached to either; Nitrogen, Oxygen or Fluorine. We would look for
H-N, H-O or H-F in the structure of the molecule. In this combination of atoms, the hydrogen has a small
positive charge, and the other atom has a small negative charge. This is called a hydrogen bond.
13. Why does the hydrogen have a positive charge, when attached to N, O or F? Look where N, O
and F are on the periodic table. Hint: Think about electronegativity.
14. Draw a hydrogen atom and an oxygen atom bonded together. Show their nucleuses and
valence electrons. Based on the difference in electronegativity, predict where the electrons
would spend the most time.
15. Molecules with hydrogen bonds are attracted to each other. Which part of one molecule is
attracted to which part of the other molecule? Think about where the charges are on the H and
the N, O or F.
16. Hydrogen bonds are much weaker than ionic bonds. What does this say about the amount of
charge on the Hydrogen?
B. There is another type of intermolecular force that is weaker than hydrogen bonds. Some molecules
have an electron thief that causes the charge to be unbalanced. If a molecule has a slightly positive
end and a slightly negative end, it is called a dipole. Molecules with dipoles are attracted to each other,
and we call the attraction dipole-dipole force – an example is hydrogen chloride (HCl). The positive end
(H) is attracted to the negative end (Cl)
17. Why is the Cl the negative end? _________________________________________
18. Based on the two descriptions, do you think hydrogen bonds could be called dipole-dipole
forces? Explain why or why not.
19. Why do you think dipole-dipole forces are weaker than hydrogen bonds? Think about the
charge.
C. The weakest of the all intermolecular forces are dispersion forces. Suppose you have a molecule
where the charge is evenly balanced all over the molecule – it is not a dipole, and doesn’t have hydrogen
bonds. Does it attract its neighbor, or not? Before you look at the answer, put your guess here:
Answer: Every molecule is attracted to its neighbor by dispersion forces. This is why even helium atoms
can stick together (if it is cold enough, -268° C). In any atom or molecule, there are electrons moving
around quickly and randomly.
Electrons can be anywhere in the atom or molecule, and they don’t always balance out –
once in a while they can all “pile up” on one side of the atom or molecule. In the picture
to the right, we have 5 electrons on the left side of the atom, but only 3 on the right.
Ne
This gives the atom a temporary (-) charge on the side with the electrons (the left), and a temporary (+)
charge on the other (the right). So it is like a dipole, but only for an instant.
20. Why does the phrase “temporary dipole” sound like a good description of these forces?
21. Would you expect these dispersion forces to be stronger or weaker than dipole-dipole forces?.
Explain.
22. Now make a list of the four forces or attractions, in order, from weakest to strongest. Go back
and look at the descriptions if you need help.
23. Water molecules have hydrogen bonds. Do water molecules attract each other strongly or
weakly? Explain:
24. Water has a high surface tension – think of the experiments with drops on a penny
or floating a paper clip. How could you use hydrogen bonding to explain this?
25. What other properties of solids, liquids or gases can be explained by the strength or weakness of
the intermolecular forces?
Applying what you learn:
Look at the table of the boiling points of noble gases. Notice that all these boiling points are way below
zero. Room temperature is about 25 °C, so any substance with a boiling point below 25 °C will be a gas
at room temperature.
Element
Helium
Neon
Argon
Krypton
Boiling point
-268 °C
-246 °C
-186 °C
-153 °C
Expected State of Matter
Gas
Gas
Gas
Gas
26. The boiling points of these noble gases are all very low. Do you think the intermolecular forces
between the atoms are strong? Or weak ? (underline one answer)
27. What type of forces do you think are between the atoms in a noble gas? Dispersion forces,
dipole-diole forces or hydrogen bond? (underline or circle all that apply)
28. Explain your answer in 24 – think about whether an atom of helium or neon should have
lopsided electrons (a dipole).
29. Predict the boiling point of Xenon, which is the next noble gas below Krypton in the periodic
table.
30. Why is Xenon also a gas – refer to the type of intermolecular forces that it has.
31. Draw two atoms of Neon, next to each other, and show how they can attract each other.
Remember drawing Lewis structures.
Comparing substances with different types of intermolecular forces.
Here is a table showing the boiling points of some other substances. Only one of these has only
dispersion forces. See if you can figure out which one. Fill in the boxes on the table.
Substance
Methane, CH4
HCl
Ammonia, NH3
Water, H2O
Boiling point
-164 °C
- 85 °C
- 33 °C
100 °C
State of Matter
Gas
Gas
Gas
Liquid
IMF(s)
32. Which one of these do you think has only dispersion forces?
33. Explain why:
______________
34. Which of these four substances do you think has dipole-dipole forces? Explain.
35. Which of these four substances do you think has hydrogen bonds?
36. You should have noticed that some molecules can have more than one type of IMF. Which IMF
is the most important if a molecule has more than one?
37. Why does water have such a high boiling point?
Comparison of Chemical bonds vs. Intermolecular forces
Let’s look at a few other materials, and compare the type of intermolecular forces. We already said
that salt is a solid. We will look at the melting points of several materials that are liquids or solids at
room temperature.
Substance
Water
Glucose, C6H12O6
LiCl
Salt, NaCl
Melting point
0 °C
150 °C
605 °C
801 °C
State of Matter
Liquid
Solid
Solid
Solid
The bond between Na+1 and Cl –1 in sodium chloride is very strong. This force or attraction keeps all the
atoms in NaCl locked in place, because each atom has a strong chemical bond to all its neighbors.
With covalent substances like water or glucose, each molecule is independent, but is attracted to its
neighbors by the intermolecular forces we have been describing. If we look at the structure of water
and glucose, we find that they both have O-H bonds.
38. Based on their elements and picture, what type(s) of IMFs do water and glucose have?
39. Based on the data in the table, which are stronger, ionic bonds or hydrogen bonds?
______________
40. Explain your answer in #39, based on what you know about intermolecular forces and charges.
Application question:
41. Explain why water should have a very high surface tension, based on intermolecular forces.
42. Why do substances with low boiling points have high vapor pressures? Also why do substances
with high boiling points have low vapor pressures? Remember vapor pressure is the pressure
caused by gas above its liquid or solid form. For example, when you have a puddle of water
some of the water molecules leave the liquid form and go into the gaseous form. The pressure
that comes from these gas molecules is called vapor pressure.