Links between Dynamic Representations of Atomic-Scale Phenomena

and Molecular Reasoning

February 2008, CHAIS conference

Dalit Levy, Robert TinkerThe Concord Consortium

The work is supported by the NSF under the TELS grant.

Today’s Presentation Outline

1. The need for a TELS project on Phase Change

2. The goals of the project

3. Research goals and questions

4. Participants and data

5. The need for a Molecular Reasoning scale

6. Results of analyzing the data using the MR scale

1. Why did we design the “Phases of Matter and Phase Change” Project?

Traditional instruction of phase change in high school chemistry classes might leave too many students with a little understanding of underlying concepts and processes. For example, in TELS 2004 benchmark assessment:• only half of the students knew that when phase change occurs the temperature stays constant • 42% of the students didn’t know that the temperature is a measure of the average kinetic energy of the molecules

In spite of prior knowledge that students have after dealing (macroscopically) with states of matter in the elementary and the middle school, many of them lack the ability to integrate the molecular (microscopic) aspect they are exposed to in their high school chemistry lessons into an elaborated conceptual account of processes of phase change (Smith, Reiser, Anderson, & Krajcik, 2006).

Goal 1 - Knowledge Integration (KI)Develop the learners’ ability to integrate knowledgeabout macroscopic and molecular properties of the three phases of matter

Goal 2 - Molecular Reasoning (MR)Enable the creation of higher level explanations ofphase change related phenomena

Instructional Technology

2-a. The goals of the “Phases of Matter and Phase Change” Project

The Phase Change project2-b. Static vs. Dynamic visualizations

Static Molecular Models (From Pearson Prentice Hall Chemistry, 2005)

Static models only partially represent atomic-scale properties. The static representation is just one specific frame of the ever-changing dynamic molecular world. In spite of prior

Students have difficulties understanding that atoms are in constant motion in solid, liquid and gas (Pallant & Tinker, 2004).

The Phase Change project2-c. Static vs. Dynamic visualizations

Dynamic Molecular ModelsThe TELS model of solid The TELS model of liquid The TELS model of Gas

Molecular Workbench models use a computing engine that lets users observe and interact directly with a sophisticated representation of the molecular world.

In TELS, these dynamic models are embedded within an inquiry activity that enables the recording of predictions before, and reflections after, the interaction with the models.

3. Research Goals and Questions

Research Goals

•Examine the level of molecular reasoning in students explanations of phase change phenomena

•Trace the changes in students’ level of molecular reasoning and their level of knowledge integration

Research Quaestion

What are the changes in the students ability to useMolecular Reasoning (MR) in their explanations of phase change phenomena?

4-a. Participants and Data

Data SourcesStudents’ answers to four pre- and post- test items, designed toassess the learners ability to employ a molecular point of view while explaining a familiar phenomenon. Overall, more than 2000 answers were examined.

Participants

• 5 TELS high schools in MA, NC, WI

• 8 teachers (7 chemistry, 1 biology)

• 313 pairs of students, grades 9-12 (diverse background)

Sample assessment itemIf you want something to dissolve fast, you should mix it with:(a) Hot water. (b) Cold water.

Explain why, referring to molecular motion.

Examples of post-test responses

Student #5: “hot water. EXPLANATION: when adding heat the molecules tend to break down faster”.

Student #18: “hot water. EXPLANATION: The hot water will break the intermolecular forces faster than the cold water will. Which will make the molecules have a less restricted range of motion”.

Examples of pre-test responsesStudent #10: “hot water. EXPLANATION: Sugar

dissolves faster in a cup of hot milk than in a cup of cold milk.”

Student #18: “hot water. EXPLANATION: the molecules move faster”.

4-b. Participants and Data

Example - item 7 in the pre/post test: What happens to water molecules when a cube of ice is takenout of the freezer and left at room temperature?

173 pre: “The molecules are heated up, and begin to move faster and the ice will melt because of the increased speed of the water molecules”

173 post: “The water molecules begin to move faster, and break apart more, therefore a smaller intermolecularforce, and it causes the ice to melt, and become wateragain.”

31 pre: “The cube of ice will melt. The warm molecules in the air go to the ice and slowly mix with the cold molecules making the ice cube melt”.

5-a. The Molecular Reasoning Scoring Rubric

Student responses were coded using a new rubric, titled the

Molecular Reasoning scaleScore Description

3 Dynamic molecular reasoning, includingcorrect description of the weakening ofintermolecular forces

2 Dynamic molecular reasoning (speakingabout molecular motion) OR understanding ofthe role of intermolecular forces in melting theice

1 Static molecular reasoning: speaking aboutmolecules, but not about their motion.Molecules separate, molecules break, andalso just including the term "molecules" in theexplanation

0 No molecular reasoning

Historical ReferencePauling (1944 Nobel prize winner) “worked from crystallographic data, and his bonds were static,

stable, and enduring”. Zewail (1999 Nobel prize winner) “has set those

bonds in motion, making them as alive and dynamic as chemistry itself” (Smith,1999)

5-b. A scale for measuring Molecular Reasoning (MR)

Keywords

3

Bond +

2

Speeding

1

Expand

Some MR scoring issues

167 pre: The arrangenment of the balls determines the phase of the matter, a tight arrangenment wouldIndicate a solid matter.Static image, scored 1.

176 pre: gas bonds are weak since the atoms are morespread out then liquid, and liquid is a weaker bond then a solidbecause solids are close together and used all togetherStatic image, but speaks of bonds - scored 2.

98 pre: In a solid the intermolecular bonds are close, in a liquid the intermolecular bonds are spread apart but don't move that fast. In a gas the intermolecular are spread far apart and mover slow.Dynamic image, scored 2.

6-a. Results

Improved ability of Molecular Reasoning (MR)

The MR score improved from pre- to post for 76% of the students.

Changes in MR from pre to post

76%

14%

10%

Positive gainNo gain Negative gain

The positive gain group started the learning with an average MR score below the static MR level and finished closer to a dynamic MR level. The other two groups were already above the static level in the pre-test.

6-b. Results

Significant change from pre to post

Within the positive gain group, the average MR level improved from 0.91 (pre) to 1.67 (post). The pairs of students in this group (76% of the pairs) clearly climbed above the static level of molecular reasoning, employing a more dynamic point of view after learning with the TELS project.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Average Pre-test MR score Average Post-test MR score

All Positive No gain Negative gain gain

6-c. Results

Distributions of MR scores in the positive gain group

Only 3 pairs showed a dynamic MR in the pre-test, and no pair expressed the highest intermolecular level. Students start the TELS Phase Change project with a little prior knowledge about molecular dynamic, and without any knowledge about intermolecular forces.

In the post-test, 18% scored 2 or higher, presenting the highest level of understanding.

Pre-test MR scores

1819

22

28

21

3332

13

3

0

5

10

15

20

25

30

35

Post-test MR scores

01

7

12

1617

19

29

27 27

10

2

4

0

5

10

15

20

25

30

35

0 .25 .50 .75 1 1.25 1.5 1.75 2 0 .25 .50 .75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3

6-d. Results

Qualitative Results

1. Pre-test responses tend to be a mix: “the molecules melt” (mixing macroscopic and molecular

aspects)“the bonds separate” (mixing molecules and bonds).

2. Pre-test responses show a clear lack of knowledge about intermolecular

forces. When using the term, it is often very wrong.

3. When is a certain phase of matter stronger than the other?Six categories were found:Harder to break is stronger; Stable is stronger;Heavier is stronger; Harder to separate is stronger.Denser is stronger; Faster is stronger;The 3 left categories reflect non-MR; the 3 right categories

reflect MR.

Thanks for listening!

1. The need for a TELS project on Phase Change

2. The goals of the project

3. Research goals and questions

4. Participants and data

5. The need for a Molecular Reasoning scale

6. Results of analyzing the data using the MR scale