Physical Science

Pure substances can be identified by properties which are independent of the sample of the substance and the properties can be explained by a model of matter that is composed of small particles.

Benchmark: Particle Model

Explain density, dissolving, compression, diffusion and thermal expansion using the particle model of matter.


Standard in Lay Terms 

All matter is made of invisibly tiny particles, a model of how matter is made.  This particle model can explain the properties of matter.  Pure subtances can be identified by their individual properties.

Big Ideas and Essential Understandings 

Big Idea:.

All matter is composed of particles that are too tiny to be seen.  We use this model as a basis to explain why 1) some materials are more dense than others, 2) some solids can dissolve in water, 3) some matter can be compressed, 4) some matter spreads out, and 5) matter expands when heated.

Benchmark Cluster 

MN Standard Benchmarks  Explain density, dissolving, compression, diffusion, and thermal expansion using the particle model of matter.


A quote, cartoon or video clip link directly related to the standard.


NSES Standards:

A substance has characteristic properties, such as density, a boiling point, and solubility, all of which are independent of the amount of the sample. A mixture of substances often can be separated into the original substances using one or more of the characteristic properties. (p. 154)

Matter is made of minute particles called atoms, and atoms are composed of even smaller components. These components have measurable properties, such as mass and electrical charge. Each atom has a positively charged nucleus surrounded by negatively charged electrons. The electric force between the nucleus and electrons holds the atom together. (9-12 Strand, p. 178)

AAAS Atlas:

Volume 1, Structure of MatterAtoms and Molecules, p. 54-55

Benchmarks of Science Literacy

The Physical Setting: The Structure of Matter

By the end of the 8th grade, students should know that

All matter is made up of atoms, which are far too small to see directly through a microscope. 4D/M1a

The atoms of any element are like other atoms of the same element, but are different from the atoms of other elements. 4D/M1b*

Atoms may link together in well-defined molecules, or may be packed together in crystal patterns. Different arrangements of atoms into groups compose all substances and determine the characteristic properties of substances. 4D/M1cd*

Equal volumes of different materials usually have different masses. 4D/M2*

Atoms and molecules are perpetually in motion. Increased temperature means greater average energy of motion, so most substances expand when heated. 4D/M3ab

In solids, the atoms or molecules are closely locked in position and can only vibrate. In liquids, they have higher energy, are more loosely connected, and can slide past one another; some molecules may get enough energy to escape into a gas. In gases, the atoms or molecules have still more energy and are free of one another except during occasional collisions. 4D/M3cd

A substance has characteristic properties such as density, a boiling point, and solubility, all of which are independent of the amount of the substance and can be used to identify it. 4D/M10** (NSES)

Common Core Standards

6.G.2. Find the volume of a right rectangular prism with fractional edge lengths by packing it with unit cubes of the appropriate unit fraction edge lengths, and show that the volume is the same as would be found by multiplying the edge lengths of the prism. Apply the formulas V = l w h and V = b h to find volumes of right rectangular prisms with fractional edge lengths in the context of solving real-world and mathematical problems.

6.EE.2. Write, read, and evaluate expressions in which letters stand for numbers.

6.EE.9.Use variables to represent two quantities in a real-world problem that change in relationship to one another; write an equation to express one quantity, thought of as the dependent variable, in terms of the other quantity, thought of as the independent variable. Analyze the relationship between the dependent and independent variables using graphs and tables, and relate these to the equation.


Student Misconceptions 

Students of all ages show a wide range of beliefs about the nature and behavior of particles. They lack an appreciation of the very small size of particles; attribute macroscopic properties to particles; believe there must be something in the space between particles; have difficulty in appreciating the intrinsic motion of particles in solids, liquids and gases; and have problems in conceptualizing forces between particles (Children's Learning in Science, 1987).

(Atlas, Vol. 1, p. 54)

Middle-school and high-school students are deeply committed to a theory of continuous matter (Nussbaum, 1985b). Although some students may think that substances can be divided up into small particles, they do not recognize the particles as building blocks, but as formed of basically continuous substances under certain conditions (Pfundt, 1981). (Atlas, Vol. 1, p. 54)

Students at the end of elementary school and beginning of middle school may be at different points in their conceptualization of a "theory" of matter (Carey, 1991; Smith et al., 1985; Smith, Snir, & Grosslight, 1987). Although some 3rd graders may start seeing weight as a fundamental property of all matter, many students in 6th and 7th grade still appear to think of weight simply as "felt weight"-something whose weight they can't feel is considered to have no weight at all. Accordingly, some students believe that if one keeps dividing a piece of styrofoam, one would soon obtain a piece that weighed nothing (Carey, 1991). Atlas, Vol. 1, p. 54)

"From an early age through to adulthood, conceptions about dissolving include the following: the solute "disappears," "melts away," "dissolves away," or "turns into water."  Older students imagine that as sugar dissolves, it "goes into tiny little bits," "sugar molecules fill spaces between water molecules, or sugar "mixes with water molecules."

"Students' ideas about what happens to sugar as it dissolves frequently fail to include the conservation of mass.  The gap between the proportion of students who conserved substance but not mass widened between the ages of 9 and 11 but narrowed in later years.  After age 12, many, but not all, students begin to develop a conception of weight and mass and begin to conserve mass off the solute."

"Students' ideas about solutions include thinking that sugar solutions are not a single phase but rather that invisible gross particles of sugar as suspended in the solution.  They may suggest that the particles can be filtered out or will settle out from the solution.  Others see the solute and solvent as a single substances rather than as a homogeneous mixture."

Keeley, Page, and Joyce Tugel. Uncovering Student Ideas in Science: 25 NEW Formative

Assessment Probes. 4. Arlington, VA: NSTA Press, 2009. pp 14-15. Print.


Students in Miss A's class are learning that some of the objects scientists study are too small to be seen with the human eye. 

When they arrive to class and find seats at the lab stations, students find one black box, taped shut, at each station.  Excitement rises as students wonder what is inside the box.  They begin to manipulate it, and soon realize that each box has a marble inside.  Miss A offers the students time to "play" with with lab material, and she encourages students to pass the box around the group and notice different sounds that the marble makes when it is rolled to different areas of the box.

After a few minutes, Miss A regroups the class and praises them for their interest in today's lab.  She writes "Black Box" on the board.  As she writes it, she explains that each black box is taped shut, and it cannot be opened.  She also points out that each black box has a marble that can roll freely when the box is moved.  In addition, each black box contains a series of cardboard shapes that are taped inside it.  The challenge of each group is to identify the type of each shape and its location within the box.

After some time, groups come up with sketches that depict their hypothesis of the shape inside their box.  Members from each group bring the box to Miss A and ask, "Is this right?"  Miss A smiles and says, "What do you think?"  This leaves the students looking perplexed, and returning to the lab station to retest their hypothesis, seeking confirmation. 

When all groups have formed a hypothesis, Miss A instructs a member from each team to draw their sketch on the board.  The class recognizes that no two sketches are the same, and every group is seeking Miss A's confirmation that their sketch is correct.

Miss A responds by saying, "Sometimes scientists need to study material that they cannot see.  Sometimes that material is very large, and sometimes it is very small."

The class brainstorms lists of materials that are too big and too small for scientists to hold in their hands and see with their own eyes.  As students make the "too small" list, a student adds, "What about those tiny particles that make up stuff?  Can we add that?"  Miss A praises his thinking and writes "Particles of Matter" on the board.

Class is ending and Miss A summarizes their learning by saying, "A black box represents material that scientists study, but cannot view with their own eyes.  Today you shared that there are many items scientists cannot actually see.  One of those items you listed is "Particles of Matter."  Particles of Matter are very small pieces that are grouped together to make something large."  As she says this, Miss A holds up a cup of water and says, "What's in this glass?"  The students say, "Water."  Miss A says, "What makes up water?"  Some students have heard of the formula "H20" but they say it with some hesitancy, not really certain what it means.  Miss A says, "Water is made up of very small particles.  Just like your lab station is made up of very small particles.  Even air is made up of very small particles.  In this unit, we are going to learn how we can study particles we cannot see and what we notice about their behaviors."


Instructional Notes 

Instructional suggestions/options:

Students need models that they can manipulate to explain phenomena they are witnessing in their investigations.  These can be desk top models or computer based models, but they should be easily accessible and easy to manipulate for students.  Other options are models where students are particles of matter and teacher guides them through a simulation to explain phenomena.

Selected activities:  Use this online simulation to explore concepts that impact the density of an object:

PhEt Density Simulation  This animation demonstrates how diffusion works in a solution.

McGraw Hill "Diffusion" Animation  Ask the students to find out what they can about expansion joints used in bridge construction, sidewalk construction, and other areas. How do power lines illustrate thermal expansion and contraction?  Consider arranging a set of stations within the classroom for students to experience the scientific vocabulary terms.  For example, at a density station, students might be provided with beakers of mystery liquids, labeled A, B, and C.  The teacher could provide the students with a list of three densities, one for each liquid.  The students could engage in a lab that requires them to layer the liquids and match the appropriate density label to each liquid.  At another station, students might be provided with various one-inch cubes, made of different materials, but all the same color.  Again, a list of densities should be provided, along with the material of the cube that coincides with each density.  Students should measure the mass and volume of each cube to determine the "mystery material."

At a dissolving station, students might be challenged to determine if a substance dissolves fastest in warm water, or very cold water. 

At a compression station, the teacher might demonstrate the concept with a small "marshmallow launcher."  Use a narrow tube, and place a marshmallow in one end.  Using a small plunger, compress the air inside of the tube until the marshmallow "launches." 

**In many cases, it is most feasible to illustrate compression with balloons.  However, many schools no longer allow the use of balloons in science labs.  Review your district policy as you consider balloon-related activities.

At a diffusion station, teach students how to waft the scent from an essential oil.  Place a few drops of oil, such as peppermint, on a cotton ball.  Demonstrate the proper way to waft a scent, and explain that it is a safe procedure when trying to smell a new chemical.  Use the lab to illustrate diffusion.

Instructional Resources 

Additional resources or links:

GEMS, Discovering Density

Students "stack" liquids on top of each other using straws stuck in slices of potatoes for inexpensive density tubes. They create mystery salt solutions for each other to test for comparitive density, and examine real life connections at the end.

New Vocabulary 


  • density--the mass per unit volume of a material
  • dissolving--breaking down a solute into a solvent to create a solution
  • compression--pushing the same number of particles into a smaller space
  • diffusion--the spread of particles from an area of high concentration to an area of low concentration until both areas are balanced
  • thermal expansion--the tendency of matter to change in volume in response to a change in temperature
Technology Connections 

States of Matter 

This is a web-based model where students can adjust pressure and temperature to three different materials and see how it effects the movement of the particles.

Use Microworlds or Scratch to have students develop their own simulations of what is happening to particles of matter as they heat up, cool down, diffuse, compress, dissolve, etc.

Cross Curricular Connections 

Personify a particle of matter and write journal entries for a week of it's "life."   Have the particle go through changes involving density, compression, diffusion, dissolving or thermal expansion each day and have the particle explain what those changes are like from its perspective in these journal pages.



These are written assessment questions that students should read and respond to after students have participated in learning activities.

1.  A student has two beakers with 50 ml of room temperature water in each.  In beaker A he adds 10 ml of salt.  In beaker B he adds 30 ml of salt.  He stirs both beakers.  All of the salt in beaker A seems to have disappeared, and most of the salt in beaker B did the same.  Use words and diagrams to explain what happened to the salt and water in both beakers.  Your drawings should show what are happening to the particles that cannot be seen.

Later the student puts 5 drops of red food coloring in beaker A and 5 drops of blue in beaker B.  The beakers' salt water in perfectly still.  What might the food coloring do if it is carefully placed on the still salt water?  How might it act differently in the two beakers?  Again, use drawings and words to explain.

2.  A student takes a small disposable plastic water bottle and dips the open end into bubble solution.  She then takes the lower end of the bottle and submerges it into a sink of hot water, being careful not to squeeze the bottle or allow the open end to go under the water surface.  After about 20 seconds a bubble starts to grow out of the mouth of the bottle.  Explain what is happening to the air particles to cause that to happen?  Explain why the bubble gets "sucked" back into the bottle when she puts it in cold water.

3.  Yet another student takes two beakers and fills one with 50 ml of ice cold water and the other with 70 ml of hot water.  A drop of food coloring is placed into each.  How do the particles of hot and cold water interact differently with the particles of food coloring and why?


Questions could be used as self-reflection or in professional development sessions.

Compare the density of coins (pennies, nickels, dimes, quarters) to the density of known metals (copper, zinc).  Use the information to determine what the coins are mostly made of.

Consider the following Paige Keeley probe.  How might you use it in your classroom.  What responses would you expect from sixth graders?  How would you expect this response to change when students reach high school?

Keeley, Page, & Tugel, Joyce. (2009). Uncovering student ideas in science: 25 new formative assessment probes, vol. 4. Arlington, VA: NSTA Press.


If observing a lesson on this standard what might they expect to see.

Think about what you look for in a math lesson where a teacher is transitioning from concrete base-10 blocks to abstract algorithms.  These lessons should be allowing students to experience these phenomena at work and struggle with explaining them.  The particle models should be introduced as a way to explain and clarify what the students are wrestling with.  The students should be working with physical models and conceptual (on paper) models.  Students should be provided numerous opportunities to use the models themselves to explain actual phenomena with matter that they are witnessing.  At this level, the details of the parts of an atom and molecules are not as important as know that matter is made of small particles that move.


Struggling Learners 

Struggling and At-Risk:

Work on at kinesthetic level.  Students should have opportunities to act out these models.  For instance:  students are moving on the carpet and are told they are particles of water moving around at room temperature.  As they are heated up they move faster.  After about thirty seconds have everyone stop where they are.  You can see that students have exceeded the boundaries of the carpet.  They have expanded their area due to their faster movement.  They can move slower and see how they need less room for that.  A hula hoop works well for sample areas, so when students are in room temperature, hot, and cold scenarios you can have everyone stop and show how many

English Language Learners 

ELL students need to have diagrams of the vocabulary available for reference in their notebooks or on the classroom walls.  They will also benefit from hearing about and seeing multiple examples of the phenomena listed in the benchmark.  Students should have ample amount of time to talk with other ELL and non-ELL students about examples from their own lives.  Investigations should occur with step-by-step directions, frequently rephrasing unclear statement and summarizing.

Digital Commons

Use your ELL students in demonstrations of labs before having students begin.

Extending the Learning 


Challenge students to go beyond the term "particle" and research atoms and molecules.  Students can construct models of simple molecules and present to class.


Have students and teachers bring in various ethnic beverages or deserts and compare their densities by taking the same volume of each and weighing.  With beverages, this could be done by stacking.  Have students examine the recipies or ingredients and discuss why some were more dense than others.

Special Education 

Work on at kinesthetic level.  Students should have opportunities to act out these models.  For instance:  students are moving on the carpet and are told they are particles of water moving around at room temperature.  As they are heated up they move faster.  After about thirty seconds have everyone stop where they are.  You can see that students have exceeded the boundaries of the carpet.  They have expanded their area due to their faster movement.  They can move slower and see how they need less room for that.  A hula hoop works well for sample areas, so when students are in room temperature, hot, and cold scenarios you can have everyone stop and show how many "particles" are fitting in a given space.



Look for examples of thermal expansion in the construction of your home with your student-- expansion joints concrete, spaces in siding to allow for expansion, etc. and discuss the importance of awareness of thermal expansion in construction.