Topic: Atoms, Molecules, and States of Matter

Below is a list of key ideas related to Atoms, Molecules, and States of Matter. For each key idea, you will find a list of sub-ideas, a list of items, results from our field testing, and a list of student misconceptions. After clicking on a tab, click on it again to close the tab.

All matter is made up of atoms.

Students are expected to know that:

  1. Matter is anything that has mass and takes up space.
  2. Matter includes all gases, liquids, and solids, which make up all living and non-living things.
  3. Light and heat are not matter.
  4. All matter—solids, liquids, and gases—is made up of discrete particles (atoms), rather than being continuous, and that these atoms are the matter rather than contained in matter. In other words, the atoms are not floating or embedded in some other substance, such as air or a liquid.
  5. Matter can exist even when it cannot be seen. For example, gases or vapors are matter even though some of them cannot be seen.
  6. Anything made up of atoms is matter.
  7. It is because atoms take up space and have mass that all matter takes up space and has mass.

Boundaries:

  1. It is not expected that students will know about the internal structure of atoms or the existence of subatomic particles and, therefore, that these subatomic particles have mass.
Percent of students answering correctly (click on the item ID number to view the item and additional data)
Item ID
Number

Knowledge Being Assessed

Grades
6–8

Grades
9–12

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AM059002

Matter is made up of atoms.

64%

72%

AM024005

If you remove all of the atoms from a chair, nothing will remain.

57%

73%

AM023005

Air is matter because it is made up of atoms.

57%

71%

AM058001

A gas, a solid, and a cell are all made up of atoms but heat is not.

53%

66%

Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

Grades
6–8

Grades
9–12

AMM070

Cells are not made up of atoms (Herrmann-Abell & DeBoer, 2008).

27%

20%

AMM107

Air does not take up space (Driver et al., 1994).

22%

16%

AMM009

Atoms or molecules are embedded in matter (Renstrom et al., 1990; Griffiths et al., 1992; Lee et al., 1993; Johnson, 1998c).

18%

13%

AMM020

Solids are not made up of atoms; especially those without visible granularity (Johnson, 1998c; Nakhleh et al., 1999; Nakhleh et al., 2005; Nakhleh et al., 2006).

10%

7%

AMM022

Matter exists only when there is perceptual evidence of its existence (Stavy, 1990).

10%

7%

AMM137

Gases are not made up of atoms (AAAS Project 2061, n.d.).

10%

7%

AMM031

Biological materials are not matter (Stavy, 1991).

9%

6%

Frequency of selecting a misconception was calculated by dividing the total number of times a misconception was chosen by the number of times it could have been chosen, averaged over the number of students answering the questions within this particular idea.

All atoms are extremely small.

Students are expected to know that:

  1. Individual atoms are much smaller than things that can be seen and even much smaller than very small things, such as dust, germs and other microorganisms, blood cells, and plant cells.
  2. This is true for all atoms.
  3. All atoms are so small that billions of them make up these small things.

Boundaries:

  1. The comparison with very small objects can be used to test students’ understanding of the relative size of atoms in relation to these objects. Students will not, however, be expected to know the actual size of atoms.
Percent of students answering correctly (click on the item ID number to view the item and additional data)
Item ID
Number

Knowledge Being Assessed

Grades
6–8

Grades
9–12

Select This Item for My Item Bank

AM025002

A grain of sand is bigger than an atom.

65%

78%

AM060003

An atom is smaller than the width of a hair, a cell in your body, and a germ.

63%

77%

AM026001

A blood cell is bigger than an atom.

63%

76%

AM061003

It would take millions of atoms to make a line across a small dot (about one millimeter in diameter).

38%

56%

Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

Grades
6–8

Grades
9–12

AMM124

A germ is smaller than an atom (AAAS Project 2061, n.d.).

17%

9%

AMM068

Cells are smaller than atoms (Tretter et al., 2006).

12%

7%

AMM125

A grain of sand is smaller than an atom (AAAS Project 2061, n.d.).

12%

8%

AMM001

Atoms/molecules are similar in size to cells, dust, or germs/bacteria (Lee et al., 1993; Nakhleh et al., 1999).

9%

8%

AMM104

The width of a hair is smaller than an atom (Tretter et al., 2006).

8%

6%

Frequency of selecting a misconception was calculated by dividing the total number of times a misconception was chosen by the number of times it could have been chosen, averaged over the number of students answering the questions within this particular idea.

All atoms and molecules are in constant motion.

Students are expected to know that:

  1. Atoms and molecules of all matter are always moving.
  2. This is true for atoms or molecules of solids, liquids, and gases.
  3. Even when objects that are made up of these atoms and molecules appear not to be moving, the atoms and molecules that make up those objects are nonetheless themselves in constant motion.
  4. The motion of atoms or molecules can include moving back and forth with respect to a fixed point, around a fixed point, and/or past each other from one fixed point to another.
  5. The motion (speed and direction) of an atom or molecule can change when it undergoes collision with another atom or molecule resulting in one speeding up and the other slowing down.
  6. Because atoms and molecules are continually colliding with each other, the atoms/molecules of the substance do not have the same speed.

Boundaries:

  1. Students are not expected to know the terms rotation, translation, and vibration.
  2. They are also not expected to know that atoms and molecules of different substances move at different speeds at the same temperature.
  3. Students are not expected to know the special case of absolute zero temperature where, according to kinetic theory, there should be no motion.

There are differences in the spacing, motion, and interaction of atoms and molecules that make up solids, liquids, and gases.

Students are expected to know that:

  1. The particles of a gas (atoms or molecules) are much farther apart than the atoms or molecules of a liquid or a solid. Because atoms or molecules of a gas are so far apart they rarely come in contact with each other. In solids and liquids, the atoms or molecules are packed closely together.
  2. Although the motion of atoms or molecules of a solid is severely restricted, the atoms or molecules are constantly moving back and forth in all directions with respect to a fixed position. In liquids, the motion of the atoms or molecules is limited but the atoms or molecules can still move rapidly back and forth with respect to a fixed point, around a fixed point, and past each other from one fixed point to another. Atoms or molecules of a gas move freely and spread out throughout the container they occupy.
  3. Similar to the pushes and pulls between magnets, atoms or molecules also push and pull on each other.
    1. In solids, the atoms or molecules pull strongly on each other and are linked together in rigid structures.
    2. In liquids, the atoms or molecules pull less strongly on each other, are more loosely connected, and form less rigid structures.
    3. In gases, the pull between atoms or molecules is so weak that they do not form structures.
  4. Hardness, flow, and compressibility are macroscopic properties for which students are expected to know the molecular reason.
    1. Solids are hard because the atoms or molecules are linked together tightly in rigid structures, not because the individual atoms or molecules are hard.
    2. The atoms or molecules of liquids can easily move past each other from one fixed point to another but do not move apart from one another and that this is why liquids flow and take the shape of their container but solids do not.
    3. Gases can be compressed because the atoms or molecules are not as close together as they could be, not because the individual atoms or molecules are soft.

Boundaries:

  1. Students are not expected to know the nature of the bonds between atoms or between molecules.
  2. They are not expected to know that atoms or molecules of a solid can sometimes move past each other.
  3. Students are not expected to know the terms rotation, translation, and vibration.
  4. They are not expected to know that plasma is a distinct state of matter, and they are not expected to know the properties of a plasma.

For any single state of matter, increasing the temperature typically increases the distance between atoms or molecules. Therefore, most substances expand when heated.

Students are expected to know that:

  1. As the temperature of a substance increases, the average distance between the atoms/molecules of the substance typically increases, causing the substance to expand.
  2. As the temperature of a substance decreases, the average distance between the atoms/molecules typically decreases, causing the substance to contract.
  3. This expansion or contraction can happen to solids, liquids, and gases.
  4. Expansion or contraction due to changes in temperature can also happen to mixtures of substances.
  5. Expansion or contraction due to changes in temperature is not permanent (e.g., objects that expand when heated then contract when cooled).
  6. The number of atoms and the mass of the atoms do not change with changes in temperature.
  7. Different substances expand and contract differently.

Boundaries:

  1. Students are not expected to know the details of the relationship between the speed of the atoms or molecules and thermal expansion.
  2. They are also not expected to know the substances that violate this rule and shrink when heated or that water will shrink when heated anywhere between 0°C and 4°C.
  3. Students are not expected to know or apply gas law equations.
  4. Because the definition of the size of an atom is varied and complex, we only expect students to know that the size of an atom or molecule does not decrease when the temperature increases and that the size does not increase when temperature decreases.
Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

Grades
6–8

Grades
9–12

AMM089

Solid substances do not expand or contract with changes in temperature (Herrmann-Abell & DeBoer, 2007, 2008).

34%

25%

AMM096

The mass of the atoms or molecules of a substance increases when the temperature increases and decreases when the temperature decreases (AAAS Project 2061, n.d.).

25%

22%

AMM122

The average distance between the atoms or molecules of a substance remains the same when the temperature of the substance changes (AAAS Project 2061, n.d.).

25%

18%

AMM038

Heat is made of "heat molecules" (Berkheimer et al., 1988).

24%

16%

AMM086

The number of atoms or molecules of a substance increases when the temperature increases and decreases when the temperature decreases (Herrmann-Abell & DeBoer, 2008).

21%

13%

AMM019

Water molecules break down when heated (Griffiths et al., 1992).

19%

14%

AMM091

The mass of the atoms or molecules of a substance increases when the temperature decreases and decreases when the temperature increases (Herrmann-Abell & DeBoer, 2007, 2008).

19%

15%

AMM129

The molecules of air break down when the air is cooled (AAAS Project 2061, n.d.).

19%

12%

AMM037

Substances shrink when heated (especially solids) (Lee et al., 1993).

15%

12%

AMM087

The number of atoms or molecules of a substance increases when the temperature decreases and decreases when the temperature increases (Herrmann-Abell & DeBoer, 2007).

16%

9%

AMM076

The size of the atoms or molecules of a substance increases when the temperature decreases and decreases when the temperature increases (AAAS Project 2061, n.d.).

14%

11%

Frequency of selecting a misconception was calculated by dividing the total number of times a misconception was chosen by the number of times it could have been chosen, averaged over the number of students answering the questions within this particular idea.

When heated, solids can change into liquids and liquids can change into gases. When cooled, gases can change into liquids and liquids can change into solids. These changes of state can be explained in terms of changes in the proximity, motion, and interaction of atoms and molecules.

Students are expected to know that:

  1. When the temperature of a liquid decreases, the average speed of the atoms or molecules decreases and, as a result, the pull that exists between the atoms or molecules is strong enough to link them together as a solid.
  2. When the temperature of a solid increases, the average speed of the atoms or molecules increases and the pull between the atoms or molecules is no longer strong enough to hold them together as a solid; the atoms or molecules are now more loosely connected as a liquid.
  3. When the temperature of a gas decreases, the average speed of the atoms or molecules decreases and, as a result, the pull that exists between the atoms or molecules is strong enough to loosely connect them together as a liquid.
  4. When the temperature of a liquid increases, the average speed of the atoms or molecules increases and the pull between the atoms or molecules is no longer strong enough to hold them together as a liquid. In this case, the pull between atoms or molecules is so weak that they are no longer connected to each other, but rather they exist as a gas.
  5. At the boiling point and freezing point, atoms or molecules from anywhere in the substance can enter the gas state and solid state, respectively. Because of this, the bubbles that form when the substance is boiling are atoms or molecules of that substance in the gaseous state.
  6. Evaporation or condensation can also occur independent of temperature; i.e., at any temperature there are some atoms or molecules that may move from one state to another at the surface of a substance. This also includes atoms or molecules on the surface of a solid that can enter the gas state.
  7. A substance is made up of the same type of atom or molecule regardless of whether it is in the solid, liquid, or gas state. There is no change in the identity of the atoms or molecules during a change of state; only the arrangement, motion, and interaction of the atoms or molecules change.
  8. Atoms or molecules are not destroyed during a change of state.
  9. Any change of state is reversible.

Boundaries:

  1. Although changes of state can be caused by changes in either temperature or pressure, students are only expected to know the effects of changes in temperature.
Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

Grades
6–8

Grades
9–12

AMM061

The molecules of a substance break down into individual atoms when the substance evaporates. During evaporation, water breaks down into hydrogen and oxygen (Bar et al., 1991; Bar et al., 1994).

39%

37%

AMM049

The molecules of a substance break down into individual atoms when the substance boils. For example, molecules of water become atoms of hydrogen and oxygen when water boils (Osborne et al., 1983; Renstrom et al., 1990).

36%

34%

AMM051

When water boils, the bubbles formed during boiling contain air, not water in the gas state (Osborne et al., 1983; Renstrom et al., 1990; Bar et al., 1991; Johnson, 1998a; Chang, 1999).

29%

26%

AMM038

Heat is made of "heat molecules" (Berkheimer et al., 1988).

25%

17%

AMM043

Molecules change shape during a phase change (Novak et al., 1991; Griffiths et al., 1992).

19%

19%

AMM015

Observable properties of the state are attributed to the individual molecules (e.g., molecules in a solid are hard; molecules move in gases and liquids, but not in solids; or the molecules of the substance change from soft to hard when a liquid freezes) (Lee et al., 1993).

23%

12%

AMM047

The identity of the molecules of a substance changes during a phase change (Lee et al., 1993).

21%

14%

AMM045

Molecules change weight/mass during a phase change (Griffiths et al., 1992).

19%

14%

AMM133

Matter is destroyed during melting (AAAS Project 2061, n.d.).

15%

10%

AMM044

Molecules change size during a phase change (Novak et al., 1991; Griffiths et al., 1992).

11%

9%

AMM132

Matter is destroyed during boiling (AAAS Project 2061, n.d.).

11%

7%

AMM131

Matter is destroyed during evaporation (Bar & Galili, 1994; Bar & Travis, 1991; Lee et al., 1993; Osborne & Cosgrove, 1983)

11%

7%

AMM063

When water evaporates from an object, that water is absorbed into the object (Osborne et al., 1983; Bar et al., 1991; Bar et al., 1994).

7%

7%

Frequency of selecting a misconception was calculated by dividing the total number of times a misconception was chosen by the number of times it could have been chosen, averaged over the number of students answering the questions within this particular idea.

For any single state of matter, the average speed of the atoms or molecules increases as the temperature of a substance increases and decreases as the temperature of a substance decreases.

Students are expected to know that:

  1. The temperature of a substance is directly related to the average speed of its atoms/molecules.
  2. Therefore, as matter in any particular state is heated, stirred, shaken, etc., the average speed of its atoms/molecules increases, which is reflected in an increase in its temperature.
  3. As matter in any particular state cools, the average speed of its atoms/molecules decreases, which is reflected in a decrease in its temperature.
  4. When the temperature of matter in any particular state remains constant, the average speed of its atoms/molecules remains constant, and when the average speed of the atoms/molecules of matter in any particular state remains constant, the temperature of the matter remains constant.

Boundaries:

  1. Students are not expected to know that temperature remains constant during a change of state, which is a later idea.
  2. They are not expected to know the term kinetic energy or that kinetic energy is a function of mass and velocity.
  3. Students are also not expected to know that atoms and molecules of different substances move at different speeds at the same temperature.
  4. They are not expected to know that increasing pressure will increase the temperature or any other application of the gas law equations.
  5. Students are also not expected to know the special case of absolute zero temperature where, according to kinetic theory, there should be no motion.