Key Idea: 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.
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

AM051005

When a sealed plastic bottle filled with air is placed in the refrigerator, the bottle becomees dented because molecules of air inside the bottle get closer together.

See the Original Project

AM073002

The molecules of hot air are farther apart than the molecules of cold air.

See the Original Project

AM045004

The molecules of cold water are closer together than the molecules of hot water.

See the Original Project

AM052005

When an iron frying pan cools, the distance between the iron atoms decreases.

See the Original Project

AM049003

The distance between water molecules increases when a cup of cold water warms up to room temperature.

See the Original Project

AM039004

The distance between water molecules increases as a cup of water is warmed.

See the Original Project

AM042005

When a glass thermometer is placed in hot water, the level of liquid rises because the molecules get farther apart.

See the Original Project

AM052004

When an iron frying pan heats up, the distance between the iron atoms increases, so the pan gets a tiny bit larger.

See the Original Project

AM046006

During a hot day in the summer, the spaces between the concrete sections of a sidewalk get narrower because the concrete sections expand.

See the Original Project

AM052003

When an iron frying pan cools, the distance between the iron atoms decreases, so the pan gets a tiny bit smaller.

See the Original Project

Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

Grades
6–8
Grades
9–12

AMM129

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

See the Original Project

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.).

See the Original Project

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.).

See the Original Project

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).

See the Original Project

AMM089

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

See the Original Project

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).

See the Original Project

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).

See the Original Project

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.).

See the Original Project

AMM038

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

See the Original Project

AMM037

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

See the Original Project

AMM019

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

See the Original Project

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.