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	Pre-Test	Post-Test
SB057001	When nitric acid and copper react, the atoms detach from one another and then link together in different ways to make the molecules of the red gas and green liquid.	40%	75%
SC035004	During a chemical reaction, atoms stay the same but rearrange to form new molecules.	36%	71%
SB004003	After a chemical reaction occurs, some of the atoms are connected to different atoms than they were in the starting molecules. (This item uses circles to represent atoms.)	18%	51%

Frequency of selecting a misconception
Misconception ID Number	Student Misconception	Pre-Test	Post-Test
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).	40%	75%
M002	During a chemical reaction, the molecules of any ending substance must always include every type of atom from the starting molecules.	35%	33%
SCM026	The atoms of the reactants of a chemical reaction are transformed into other atoms (Andersson, 1986).	29%	11%
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).	8%	4%
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).	5%	3%

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.