Content Benchmark P.12.A.1
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Students know different molecular arrangements and motions account for the different physical properties of solids, liquids and gases. E/S.

Some Background about Energy
According to the Kinetic Molecular Theory (KMT), matter is composed of tiny particles (atoms, molecules, or ions) with definite and characteristic sizes that do not change. The energy and organization of these particles determines the physical state and bulk physical properties of a particular sample of matter.

For more information about the Kinetic Molecular Theory, see http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch4/kinetic4.html.

All particles are in constant, random motion. In other words, all particles possess kinetic energy. The amount of kinetic energy is directly related to Kelvin temperature. With a higher temperature, the particle possesses more kinetic energy. Kinetic energy is transferred from one particle to another through collisions.

Particles also interact with each other through attractions and repulsions because they have either permanent or temporary dipoles. Overall, molecules tend to orient themselves to align the partial positive charge on one molecule with a partial negative charge on another molecule (“opposites attract”). The physical separation of these charges results in electrostatic potential energy. The strength of the attractions between the particles (the intermolecular attractions) in a sample of matter is determined by the bonding, shape, and polarity of the molecule.

For more information about intermolecular attractions, see http://chemed.chem.purdue.edu/genchem/topicreview/bp/intermol/intermol.html.

The interaction between the particles’ kinetic and potential energies determines how the particles interact, how the particles are arranged relative to each other, and the bulk physical properties of the matter the particles compose.

States of Matter
There are different physical states of matter. Here, we focus on the three that are most common in our everyday experiences: solids, liquids, and gases.

Figure 1. Microscopic representations of the three common states of matter (From http://www.ilpi.com/msds/ref/gifs/statesofmatter.gif)

Solids. This state of matter is characterized by a dominance of potential energy over kinetic energy. In solids, there are strong intermolecular attractions that hold individual particles together. These particles do not have sufficient kinetic energy to overcome the strong intermolecular attractions. This does not mean that the particles are motionless. In fact, the particles in a solid are located close to each other (due to the strong intermolecular attractions) and vibrate about fixed sites.

Because their particles are held in fixed locations, solids have defined volumes and shapes and do not flow. Because their particles are close together, solids have high densities (a large amount of mass in a small volume) and small compressibilities (particles cannot be pushed much closer together than they already are). Because the particles are held together by strong intermolecular attractions, solids have small thermal expansions (the bulk sample does not expand because the particles do not move away from each other much when they are heated).

Liquids. This state of matter is characterized by potential and kinetic energies that are comparable. The particles in a liquid are randomly packed and close to each other. The intermolecular attractions between the particles are not as strong as they are in solids. The particles have enough kinetic energy to temporarily break the intermolecular attractions and slide over each other, but they do not have enough kinetic energy to completely separate from each other.

Because their particles are close together and can slide over each other, liquids have a definite volume but an indefinite shape (liquids take the shape of as much of their containers as they fill). They are also capable of flow. In fact, the higher the temperature of the liquid, the more kinetic energy the particles have and the more easily intermolecular attractions are broken so the particles can slide over each other (lower viscosity). The close packing of the particles gives liquids high densities (a little less than that of solids) and small compressibilities. The intermolecular attractions between particles in a liquid, though less strong than those in solids, keep particles close together, even when they are heated (small thermal expansion).

Gases. This state of matter is characterized by a dominance of kinetic energy over potential energy. The intermolecular attractions between particles in a gas are very small (they are ignored in many simple gas law calculations), so the particles have enough kinetic energy to move far apart from each other. The distance between particles is usually much greater than the size of individual gas particles. The particles are in constant, random motion, essentially independent of each other.

The particles in a gas are not limited to any specific shape or volume by intermolecular attractions. Gases take the shapes and volumes of their containers. Because their particles are so far apart from each other, gases exhibit low densities (relatively few particles in a given volume, compared to a solid or a liquid), large compressibilities (because particles are separated by a lot of empty space, they can be pushed closer together), flow (particles can move past each other because of the very low intermolecular attractions), and moderate thermal expansions (when gases are heated, the kinetic energy of their particles increases and particles can move further away from each other, causing the bulk sample to increase in volume).

Table 1. Summary of solid, liquid, and gas characteristics

Phase Changes/Transitions
Matter can change from one state to another as it is cooled or heated. The names of the different phase changes and the heat loss and gain associated with them are summarized in Figure 2.

Figure 2. Phase changes (Modified from http://www.ccrc.sr.unh.edu/~stm/AS/Common/Water_Phases.JPG)

Heating or cooling a substance changes the amount of energy its particles have; as heat is added, the energy of the particles increases. When heat is added to a solid, the vibration of the particles increases; but the particles remain locked in place (and the solid retains its shape) until enough energy is added to break the intermolecular attractions that keep the particles in place, at which point the solid melts.

In liquids, there are still intermolecular attractions between particles, but they are not as strong as those in solids. They are more easily broken. As heat is added to a liquid, the particles gain energy that allows the intermolecular attractions to be broken more frequently and more easily. This allows the particles in the liquid to slide or flow over each other more easily as the temperature increases. When the kinetic energy of the particles exceeds the forces required to keep the molecules close together, the liquid boils/evaporates. Any heat added at this point simply increases the kinetic energy of the particles in the gas.

For a discussion of the difference of boiling and evaporation, see http://www.launc.tased.edu.au/online/sciences/agsci/essoil/boiling.htm.

Heating and Cooling Curves
Phase transitions occur at specific temperatures when the energy of particles exceeds that allowed for a given state. When heat is added to a substance, the solid to liquid transition occurs at the melting point, when particles have enough energy to temporarily break intermolecular attractions. The liquid to gas transition occurs at the boiling point, when particles have enough energy to completely overcome intermolecular attractions.
When a substance is cooled and energy is removed from the system, the liquid to solid transition occurs at the freezing point, which is the same temperature as the melting point. The gas to liquid transition occurs at the same temperature as the boiling point, a temperature sometimes referred to as the condensation point.

Heat added to a system can have one of two effects on a bulk sample: (1) it can increase the temperature of the sample or (2) it can cause a phase change (provide the energy needed to break intermolecular attractions). It cannot have both effects at the same time. Temperature does NOT change during a phase transition. The results of heating a substance are visualized in a heating curve (see Figure 3).

Figure 3. Generic heating curve (From http://library.thinkquest.org/C006669/media/Chem/ img/Graphs/HeatCool.gif)

The heating curve consists of a series of diagonal lines and plateaus. The diagonal lines represent changes in temperature, and the plateaus represent phase changes. A sample of matter begins as a solid when it is at a temperature lower than its melting point (segment A). As heat is added, the temperature of the substance increases. Once the temperature reaches the melting point, the solid/liquid phase transition occurs, during which there is no change in temperature (segment B). When all of the sample has melted, additional heat causes an increase in the temperature of the liquid (segment C) until the boiling point is reached. At this point, all added energy is used to break intermolecular attractions between particles (segment D). Once the attractions are broken, any heat energy added will increase the temperature of the gas (segment E).

Note: Cooling curves (starting at higher temperatures and ending at lower temperatures) can also be drawn. For an example of a cooling curve, see http://www.wpbschoolhouse.btinternet.co.uk/page03/3_52states/Image86.gif).

For more information about states of matter and phase changes, see the Visionlearning site about states of matter, which gives an excellent narrative description of the different states of matter and of phase changes. It also has links to pictures of different states of matter that can be “magnified” until representations of particles can be seen. http://www.visionlearning.com/library/module_viewer.php?mid=120

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Content Benchmark P.12.A.1

Students know different molecular arrangements and motions account for the different physical properties of solids, liquids, and gases. E/S

Common misconceptions associated with this benchmark:

1. Students incorrectly believe that gases have no mass

Many students believe that gases have no mass since they cannot usually be seen and because they seem to “disappear.” Gases do have mass, although that mass is spread out over a large area since the particles in a gas are separated from each other by large distances (giving gases small densities).

This concept is discussed in a book about chemistry misconceptions at http://www.chemsoc.org/pdf/LearnNet/rsc/miscon.pdf.

Several activities can be used to address this misconception, including one from the American Chemical Society:
http://www.chemistry.org/portal/resources/ACS/ACSContent/
education/wande/resourcechem/matter/Matter_Act_6.pdf.

2. Students incorrectly believe that the particles in a solid are motionless.

Many students believe that the particles in a solid do not move since the bulk sample does not appear to move; however, all particles (in solids, liquids, and gases) move because they have kinetic energy. Particles in solids vibrate about fixed sites. The vibrations are so small we can’t see them.

For a detailed discussion of and activity about vibrational, rotational, and translational motion, see http://academic.pgcc.edu/~ssinex/molecules_in_motion.htm.  You will need Chime (http://academic.pgcc.edu/psc/chime_guide.html) to look at the accompanying pictures.

3. Students do not understand that there is empty space between particles in a gas.

Many students have difficulty accepting the idea that there can be “empty space.” Therefore, since they know that particles in a gas are far from each other, they assume that there must be something between the particles instead of nothing.

To read a paper in which researchers examined the bulk ideas about matter that makes it hard for students to accept the idea of empty space, see
http://hi-ce.org/presentations/documents/MerrittetalNARST2007.pdf.

4. Students incorrectly believe that individual particles shrink when cooled or swell when heated.

Students might assign bulk properties to individual particles. For example, they might assume that particles expand when heated because the bulk sample expands when heated. The students do not seem to understand that the expansion of a bulk sample is the result of particles moving further apart from each other and contraction is the result of particles moving closer together.

To see a unit about states of matter that was specifically designed to address this misconception, please see http://cps.bu.edu/education/vmdl/workshops/projects/2003/session2/phasechanges/word_document.doc.

5. Students incorrectly believe that particles decompose during boiling.

Several studies have shown that students believe that the bubbles in boiling water contain air, oxygen or hydrogen (or some combination of these) instead of steam. This indicates that students incorrectly believe that intramolecular bonds (those within the molecule) are broken during the liquid/gas phase change. However, intermolecular attractions are much weaker than intramolecular bonds. During a phase transition, the intermolecular attractions are broken, but the intramolecular bonds remain intact.

This misconception is addressed in question #6 of the Chemical Concepts Inventory and can be found at http://jchemed.chem.wisc.edu/JCEDLib/QBank/collection/
CQandChP/CQs/ConceptsInventory/Concepts_Inventory.html

To listen to an Orange County Department of Education podcast about this misconception, go to
http://science.ocde.us/audio/BOILINGWATER.MP3.

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Content Benchmark P.12.A.1

Students know different molecular arrangements and motions account for the different physical properties of solids, liquids, and gases. E/S

Sample Test Questions

1^st Item Specification: Given a diagram, choose the molecular arrangement that best describes a solid, liquid, or gas.

Depth of Knowledge Level 1

1. Use the following diagrams to answer the question below.

Diagram 1	Diagram 2
Diagram 3	Diagram 4

Which of the diagrams best describes the molecular arrangement of oxygen?

1. Diagram 1
2. Diagram 2
3. Diagram 3
4. Diagram 4

2. Use the following diagrams to answer the question below.

Diagram 1	Diagram 2
Diagram 3	Diagram 4

Which of the diagrams best describes the molecular arrangement of a mineral?

1. Diagram 1
2. Diagram 2
3. Diagram 3
4. Diagram 4

Depth of Knowledge Level 2

3. What is the molecular arrangement like in a liquid such as rubbing alcohol and why?
1. The molecules are close together because of their strong intermolecular attractions and low kinetic energy.
2. The molecules are randomly packed together, but the molecules can slip and slide over each other.
3. The molecules are close together because the kinetic energy is dominant over the potential energy within the molecules.
4. The molecules are far apart because of their weal intermolecular attractions and high kinetic energy.

4. What is the molecular arrangement like in wood and why?
1. The molecules are close together because of their strong intermolecular attractions.
2. The molecules are randomly packed together because the molecules can slip and slide over each other.
3. The molecules are close together because the kinetic energy is dominant over the potential energy within the molecules.
4. The molecules are far apart because of their small intermolecular attractions.

2^nd Item Specification: Recognize the differences between solids, liquids, and gases.

Depth of Knowledge Level 1

5. Which of the following describes the differences between solids and liquids?
1. Both have a definite shape, but only solids have a definite volume.
2. Both have a definite volume, but only liquids have a definite shape.
3. Solids have definite volume and shape, but liquids only have a definite volume.
4. Liquids have a definite volume and shape, but solids only have a definite shape.

6. Which of the following best describes the differences between liquids and gases?
1. Both have a definite volume, but only liquids have a definite shape.
2. Both have a definite shape, but only gases have a definite volume.
3. Gases have a definite volume only and liquids do not have either.
4. Liquids have definite volume only and gases do not have either.

Depth of Knowledge Level 2

7. A student wants to test a mystery substance to find out what state of matter it is. Which characteristics can be used to determine its state?
1. Volume, density, compressibility, and flow.
2. Volume, density, compressibility, and mass.
3. Shape, flow, and temperature.
4. Shape, density, and temperature.

8. A student has run tests on a mystery substance and has found that is has a definite volume, high density, and flows easily. Which state of matter is it and why?
1. It is a solid because it has a definite volume and high density.
2. It is a liquid because it has a definite volume and high density.
3. It is a solid because it has a definite volume and flows easily.
4. It is a liquid because it has a definite volume and flows easily.

3^rd Item Specification: Analyze the motion of particles in solids, liquids, and gases.

Depth of Knowledge Level 1

9. Which of the following correctly describes the motion of particles in a solid?
1. They do not move at all.
2. They move rapidly around in random patterns.
3. They vibrate in a set pattern.
4. They flow easily, but slowly around each other.

10. Which of the following correctly describes the motion of particles in a gas?
1. They do not move at all.
2. They move rapidly around in random patterns.
3. They vibrate in a set pattern.
4. They flow easily, but slowly around each other.

Depth of Knowledge Level 2

11. What is happening to the particles of a solid as it changes phase into a liquid?
1. They slow down and spread apart because energy is being added.
2. They slow down and become closer because energy is being removed.
3. They speed up and spread apart because energy is being added.
4. They speed up and become closer because energy is being removed.

12. What is happening to the particles of a gas as it changes phase into a liquid?
1. They slow down and spread apart because energy is being added.
2. They slow down and become closer because energy is being removed.
3. They speed up and spread apart because energy is being added.
4. They speed up and become closer because energy is being removed.

4^th Item Specification: Explain properties of the states of matter using kinetic-molecular theory.

Depth of Knowledge Level 1

13. Which of the following describes a state of matter that has a fixed molecular arrangement and particles that are close together?
1. A substance that has a strong attraction between particles and low kinetic energy.
2. A substance that has a strong attraction between particles and high kinetic energy.
3. A substance that has little attraction between particles and high kinetic energy.
4. A substance that has little attraction between particles and low kinetic energy.

14. Which of the following describes a state of matter that has a random molecular arrangement and particles that are far apart?
1. A substance that takes the shape of its container and is NOT easily compressed.
2. A substance that has a definite shape and is easily compressed.
3. A substance that takes the shape of its container and is easily compressed.
4. A substance that has a definite shape and is NOT easily compressed.

Depth of Knowledge Level 2

15. According to the kinetic-molecular theory, the particles in Ideal gases
1. behave like tiny discrete particles in a state of constant, random motion.
2. behave like hard, spherical objects in a state of constant, patterned motion.
3. lose some energy when they collide with each other or with the walls of the container.
4. have a strong force of attraction between the particles and the walls of the container.

16. Which of the following is not part of the kinetic molecular theory of gases?
1. Attractive and repulsive forces between gas molecules are negligible.
2. Gases consist of molecules in continuous random motion.
3. Collisions between gas molecules do not result in loss of energy.
4. Matter is conserved in ordinary chemical reactions.

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Content Benchmark P.12.A.1

Students know different molecular arrangements and motions account for the different physical properties of solids, liquids, and gases. E/S

Answers to Sample Test Questions

1. B, DOK level 1
2. A, DOK level 1
3. B, DOK level 2
4. A, DOK level 2
5. C, DOK level 1
6. D, DOK level 1
7. A, DOK level 2
8. D, DOK level 2
9. C, DOK level 1
10. B, DOK level 1
11. C, DOK level 2
12. B, DOK level 2
13. A, DOK level 1
14. C, DOK level 1
15. A, DOK level 2
16. D, DOK level 2

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Content Benchmark P.12.A.1

Students know different molecular arrangements and motions account for the different physical properties of solids, liquids and gases. E/S.

Intervention Strategies and Resources

The following is a list of intervention strategies and resources that will facilitate student understanding of this benchmark.

1. Interactive Animation of Phase Changes
This interactive animation allows students to “melt” or “boil” a sample and then look at the result of the phase transition at a microscopic level.

http://www.harcourtschool.com/activity/states_of_matter/

2. Simulation of Molecular Movement within Solid, Liquid, and Gas state.
This site is managed by Visionlearning, a company supported by the National Science Foundation and US Department of Education. This site provides a fine overview of the states of matter and the Kinetic Molecular Theory of Matter.

To access this background information and Flash simulations, go to
http://www.visionlearning.com/library/module_viewer.php?mid=120

3. Interactive Animation of Heating Curve
This interactive animation allows students to visualize what happens to particles as heat is added to a substance. The animation is tied to a heating curve.

http://www.footprints-science.co.uk/states.htm

4. Assessment about Students’ Understanding of the Particulate Nature of Matter
This diagnostic test was designed to assess students’ understanding of the particulate nature of matter.

http://jchemed.chem.wisc.edu/JCEDlib/QBank/collection/ CCInventory/JCE2006
p0954QB/JCE2006p0954W.pdf

5. States of Matter Mini-Module
This mini-module about states of matter is well-grounded in the literature. Molecular Workbench software allows students to visualize the particles in different states of matter. Activities help students connect macroscopic properties to microscopic arrangements of particles.

http://workbench.concord.org/web_content/states_of_matter/index.html (mini- module)

http://mw.concord.org/modeler/index.html (Molecular Workbench software)

6. States of Matter Unit
This module about states of matter also covers intermolecular attractions, temperature and states of matter, and boiling and freezing points. The unit includes assessments, a list of words for creation of a concept map, and grading rubrics. Virtual Molecular Dynamics Laboratory (VMDL) software allows students to visualize the particles in different states of matter.

http://cps.bu.edu/education/vmdl/workshops/projects/
2004/session1/3._states_of_matter_and_phase_change/activity.doc (units)

http://cps.bu.edu/education/vmdl/software/vmdl.html)
(Virtual Molecular Dynamics Laboratory software)

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