Science Assessment ~ Ideas ~ A pure 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.

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

Sub-Ideas
Items & Student Performance
Misconceptions
NGSS

Students are expected to know that:

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.
If the atoms are not rearranged, then a chemical reaction has not occurred.
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:

The idea that the number of each kind of atom stays the same will be assessed under Idea H (conservation of matter).
Students are not expected to know the term “bond” or how chemical bonds are formed or broken during chemical reactions.
They are not expected to know that during chemical reactions, atoms are not turned into energy.

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
SC066005	When two white powders react to form a yellow powder, the yellow powder is made up of the same kinds of atoms as the white powders, but the atoms are combined into different molecules.	47%	57%
SC060004	Carbon atoms are not part of the products of the reaction between sulfur and oxygen. (This item uses circles to represent atoms.)	48%	52%
SC093003	During a chemical reaction, atoms stay the same but rearrange to form new molecules. (This item uses circles to represent atoms.)	39%	50%
SC070004	During a chemical reaction, atoms stay the same but rearrange to form new molecules. (This item uses circles to represent atoms.)	38%	48%

Frequency of selecting a misconception
Misconception ID Number	Student Misconception	Grades 6–8	Grades 9–12
SCM025	The reactants and products of a chemical reaction are different and independent of each other. There is no recognition of a change of one sample to the other (Johnson, 2000b).	11%	9%
SCM026	The atoms of the reactants of a chemical reaction are transformed into other atoms (Andersson, 1986).	48%	40%
SCM021	After a chemical reaction, the product is a mixture in which the old substances persist, and is not a new substance (Johnson, 2000b; Solomonidou & Stavridou, 2000).	17%	13%
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).	17%	15%
SCM015	Substances can change their characteristic properties but maintain their identity (Pfundt, 1982). The products of a chemical reaction are the same substances as the reactants but with different properties (Solomonidou et al., 2000).	25%	19%

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.

NGSS Statements
Code	Statement
PS1.B MS	Substances react chemically in characteristic ways. In a chemical process, the atoms that make up the original substances are regrouped into different molecules, and these new substances have different properties from those of the reactants.