Content Benchmark P.8.A.1
Students know particles are arranged differently in solids, liquids, and gases of the same substance. E/S
Matter makes up every object, material, and substance in the universe and is composed of building blocks known as atoms. A more careful definition of matter is anything that has both mass and volume. Mass is the quantity of matter in an object, while volume is the amount of space the object occupies. Mass and volume are physical properties, but both physical and chemical properties identify matter. For example, all materials exist in various states.
Figure 1.Boiling liquid water is thrown into the extremely cold air creating clouds of steam and a shower of ice crystals. On Earth, water can exist as a solid, liquid and gas at the same time.
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These different states are determined by the amount of energy present in the system. Energy is the ability to do work or cause change, and is found in several forms, but kinetic energy is the form that is most valuable in terms of explaining what happens to a state of matter as it is changed from one to another. Within the various states of matter particles are in a constant motion. In liquids and gases, this motion is known as the Brownian motion, where particles move randomly while suspended in a fluid. Even in solids, molecules continually move. Generally, the movement in solids is a vibration around a fixed point and not the more free flowing movement of Brownian motion found in liquids and gases.
To learn more about Brownian motion and the states of matter, go to
It then is essentially the rate of movement of particles that determines the state of a substance. Energy must then be added (or removed) for a substance to change state. Increasing or decreasing the amount of kinetic energy present in the substance determines whether or not it is referred to as a solid, liquid, gas, or plasma. Water is one substance on Earth that commonly exists as a solid (commonly called ice), liquid (commonly referred to as water), and gas (commonly called water vapor). Each individual state will be discussed in more detail below.
Figure 2. Phases of Matter represented by the type of molecular motion found at different temperatures.
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Figure 3.Example of a phase diagram–a plot that illustrates the phases of a
substance in relation to the pressure and temperature.
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Solids have a definite shape and fixed volume. Within a solid, the molecules are tightly packed, held in relatively fixed positions, and have little kinetic energy. The intermolecular forces and strength of bonds within a solid are what enable particles to be held in relatively fixed positions.
To view an example of a solid retaining its shape and volume, go to the link below which shows the molecular structure of water ice crystals.
(scroll down to the visualization that shows water ice.)
Liquidshave weaker molecular bonds than those of solids and allow molecules to move more freely within the substance. Similar to solids, liquids have a fixed volume. However, because the intermolecular forces are weaker than solids, liquids will take the shape of their container, assuming the liquid is under the influence of gravity. Television is a great source to see the physical properties of liquids with all of the commercials demonstrating the absorbent ability of certain materials, such as paper towels. Usually in these commercials, liquids freely flow across a surface, and continue to do so, until the liquid reaches a barrier. Liquids flow because they lack a definite shape. For a given substance, the internal molecular motion is greater in a liquid than a solid, and therefore, the average molecular kinetic energy is greater in a liquid than in a solid.
In the example animation below, we see that liquid water is made up of molecules that move relatively freely, yet remain relatively close in distance to each other.
(scroll down to the simulation that shows liquid water.)
Gases are a third state of matter, and compared to solids and liquids, have weak intermolecular forces.Because of their relatively weak molecular forces, gases move rapidly through space and have a relatively high average molecular kinetic energy. Gases have no definite volume or shape, and therefore,fill a container and take the shape and volume of that container. In order for liquid water to become water vapor—a gas—energy must be transferred into the liquid, raising the average kinetic of the water molecules, allowing the water to boil, and change its state to a gas. Similar to water vapor, steam is also water in the gaseous state, but unlike water vapor, the temperature of steam is greater than the boiling point.
To view an example simulation of the behavior of water molecules entering the gas state, go to the link below
(scroll down to the visualization showing steam.)
The following table is good summary of the differences between solids, liquids, and gases when examined at the microscopic level.
Some Characteristics of Gases, Liquids and Solids and the Microscopic Explanation for the Behavior(From:
gas / Liquid / Solid
assumes the shape and volume of its container
particles can move past one another / assumes the shape of the part of the container which it occupies
particles can move/slide past one another / retains a fixed volume and shape
rigid - particles locked into place
compressible
lots of free space between particles / not easily compressible
little free space between particles / not easily compressible
little free space between particles
flows easily
particles can move past one another / flows easily
particles can move/slide past one another / does not flow easily
rigid - particles cannot move/slide past one another
To learn more about the states of matter, including the particle arrangements within each state, relative kinetic energy quantities between the states, and how matter changes state, go to
Content Benchmark P.8.A.1
Students know particles are arranged differently in solids, liquids, and gases of the same substance. E/S
Common misconceptions associated with this benchmark
1. Students incorrectly believe that materials can only exhibit properties of one state of matter.
Water is unique in that it is the only natural substance that is found in all three states— liquid, solid (ice) and gas (water vapor and steam) –at the temperatures normally found on Earth’s surface. Earth's water is constantly interacting, changing, and in movement. However, students think of water only in its liquid form, and fail to understand that water can also be a solid (ice) or gas (water vapor and steam). Students can work through this misconception, by doing investigations with water as the substance changes temperatures. For example, students may measure the temperature of ice, where the ice is located on a beaker and hot plate. As energy is transferred from the hot plate to the water, they can continue to measure temperature of the water as it changes phase. When the water begins to boil, they can they take the beaker off of the hot plate and measure the temperature decease. When the water become cooler, the students can place the beaker in a freezer, again taking temperatures and noticing changes in state as the water freezes. If the students mass the ice at the beginning and end of the experiment, they can postulate that some of the water mass was lost to the environment as steam and water vapor.
To learn more about this misconception, go to
2. Students inaccurately assume that gases are not matter because most are invisible.
Oxygen is a gas found in our atmosphere that is colorless and odorless. But oxygen is required for us to live. Indeed, all the gases comprising a pollution-free atmosphere are colorless and odorless. Because atmospheric gases are colorless and odorless, students believe that gases are just empty space (e.g., a vacuum) and are not matter. However, students can become aware that gas is matter by having them conduct experiments and view demonstrations showing that gases have mass and take up space (i.e., fill a volume). If this is the basic definition of all matter, then students can begin to understand that matter is not just empty space.
Further support concerning this misconception can be found at
3. Students have difficulty understanding that particles of solids have motion.
Solids are formed when the attractive forces between individual molecules are greater than the energy causing them to move apart. Individual molecules are locked in position near each other, and cannot move past one another. The atoms or molecules of solids remain in motion. However, that motion is essentially limited to vibrational energy; individual molecules stay fixed in place and vibrate next to each other. As the temperature of a solid is increased, the amount of vibration increases, but the solid retains its shape and volume because the molecules are locked in place relative to each other. Students should be allowed to view microscopic images that demonstrating particle movement within solids. Other experiments with solids can reinforce that molecular movement occurs in solids, specifically by looking at substances that have some solid properties and some liquid properties (e.g., silly putty or “oobleck”)
More information about this misconception can be found at
4. Students have difficulty understanding that mass and volume, both describing an "amount of matter,” are not the same property.
Mass is a measure of the quantity of matter present in an object. Volume is a measure of how much space it occupies. Mass can be measured on an instrument called a balance—that is, the object whose mass is sought is placed on one side of a see-saw like device and smaller reference masses (objects) are placed on the other side until the balance swings freely at equilibrium. The volume of an object can sometimes be determined by measurement of its various dimensions followed by a calculation of its volume based on a suitable formula. For example, a box has a volume that is the product of its length, width, and height, V = L×W×H. Volume of irregular solid objects can also be measured by the amount of water displaced by the object. It would be incorrect to assume that any small object is of low mass—and just as incorrect to assume that any large object is of high mass. The concept of density is at the heart of this issue.
For more details about this misconception, go to
Content Benchmark P.8.A.1
Students know particles are arranged differently in solids, liquids, and gases of the same substance. E/S
Sample Test Questions
Questions and Answers to follow on separate document
Content Benchmark P.8.A.1
Students know particles are arranged differently in solids, liquids, and gases of the same substance. E/S
Answers to Sample Test Questions
Questions and Answers to follow on separate document
Content Benchmark P.8.A.1
Students know particles are arranged differently in solids, liquids, and gases of the same substance. 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. Solid, Liquid, Gas Interactive Applets
The British Broadcasting Corporationhas produced “KS2 Bitesize Revision.” This site includes curriculum content, interactive simulations, and classroom lessons, which present a perspective on the states of matter.
This site is found at
The matter unit has two modules that relate to (1) gases, liquids and solids and (2) solids and liquids, both which specifically relate to this benchmark. The direct links to these two interactive applets are:
- Gases, Liquids, and Solids
- Solids and Liquids
2. The Atoms Family
The Science Learning Network and the Museum of Science, Inc. have developed a web page devoted to educational activities relating to different forms of energy, presented by famous gothic horror characters. The site contains a section focused on principles of atoms and matter. This area allows the student to work through an interactive activity, whichtests the student’s knowledge of how the element or molecule changes phases at different temperatures in a chamber.
The site can be found at
3. States of Matter and Flight
NASA’s GlennResearchCenter has an excellent site covering the physics of flight, called the Beginner’s Guide to Aeronautics. Included at the site, is a concise discussion and interactive Java™ applets, where students can do virtual experiments. This site also has excellent information on force and motion and would be an appropriate resource for long-term review of several physical science concepts in a single setting. To use this site, students will need access to computers with Java™.
To access the states of matter section of this website, go to
4. States of Matter Investigations
The University of California, San Francisco has created a series of hands-on, inquiry-based investigations covering the states of matter. These lessons go over the basics of the properties of matter, as well as investigations about the change of state. Each lesson has a listing of the required resources needed to conduct the investigations, with background information for teachers and students.
To download these lessons, go to
5. Chemistry Visualizations
The MoreChemistry.com site has several visualizations that can be used to understand fundamental chemistry better. Included are states of matter visualizations that students can use to see how particle motion differs in each state for a given substance. One excellent visualization shows what happens under very high temperature and high pressure situations that cannot be simulated in a normal middle school classroom. In this way, students can relate these two important properties to solids, liquids, and gases. To use this site, students will need access to computers with Java™.
This site can be found at (make sure you scroll down to the states of matter link).