Key Idea: When substances interact to form new substances, the atoms that make up the molecules of the original substances rearrange into new molecules.
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Whenever atoms interact with each other, regardless of how they are arranged or rearranged, the total mass stays the same.

These items have been aligned to more than one key idea. To view the sub-ideas click on a key idea below.

  • When substances interact to form new substances, the atoms that make up the molecules of the original substances rearrange into new molecules.

    Students are expected to know that:

    1. During a chemical reaction the atoms that are linked together in molecules (or arranged in other patterns such as arrays and crystals) rearrange to make new molecules.
    2. If the atoms are not rearranged, then a chemical reaction has not occurred.
    3. New substances are made of the same kinds of atoms as the original substances (i.e., the atoms themselves did not change during the reaction).

    Boundaries:

    1. The idea that the number of each kind of atom stays the same will be assessed under Idea H (conservation of matter).
    2. Students are not expected to know the term “bond” or how chemical bonds are formed or broken during chemical reactions.
    3. They are not expected to know that during chemical reactions, atoms are not turned into energy.
  • Whenever atoms interact with each other, regardless of how they are arranged or rearranged, the total mass stays the same.

    Students are expected to know that:

    1. Atoms are not created or destroyed when substances mix, undergo chemical reactions, change state, or dissolve, or when objects are cut or broken into smaller pieces.
    2. The total number of each kind of atom always remains the same regardless of what happens to the matter (mixing, chemical reactions, changes of state, dissolving, or objects being cut or broken into smaller pieces).
    3. The mass of an atom does not change.
    4. If the measured mass has changed, it is because some atoms have not been accounted for.

    Boundaries:

    1. Students are not expected to know that mass is not conserved in energy-mass conversions such as nuclear reactions or other subatomic interactions.
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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Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

Grades
6–8

Grades
9–12

SCM083

New atoms are created during chemical reactions (AAAS Project 2061, n.d.).

See the THSB Project

SCM026

The atoms of the reactants of a chemical reaction are transformed into other atoms (Andersson, 1986).

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SCM016

The products of a chemical reaction, though unseen, must have somehow existed from the start in another location, such as in the air or inside the reactants (Andersson, 1986; Solomonidou et al., 2000).

See the THSB 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.