AAAS Science Assessment ^beta

Students are expected to know that:

1. Note: The term “characteristic property” is used to emphasize that these properties are defining attributes that are independent of the amount of the sample, regardless of time, location, size, or shape.
2. The term “substance” means a pure material that is made of the same matter throughout. This is in contrast to the common definition that equates substance with matter that could be made of either a single substance or a mixture of more than one substance. To make this explicit, the phrase “pure substance” is used in assessment items.
3. A substance can be a solid, a liquid, or a gas.
4. Every substance has a set of characteristic properties that are always the same for that substance, regardless of time, location, shape, or size.
5. Furthermore, characteristic properties are consistent throughout a sample of a substance.
6. Characteristic properties with which students should be familiar are boiling point, melting and freezing point, solubility (i.e. how much of the substance can dissolve in water), flammability (i.e. the ease with which a substance will catch on fire), odor, color, and density (i.e., that equal volumes of different substances have different masses).
7. Weight, mass, volume, shape, length/width, texture, and temperature are not characteristic properties of substances and may change.
8. The characteristic properties of a substance do not change when temperature and pressure remain the same.
9. No two substances can have the same set of characteristic properties under the same conditions and that if two materials have even one different characteristic property, they are different substances.

Boundaries:

1. Students are not expected to know that the properties of substance can be different at the nanoscale.
2. They are not expected to know the formula for density (density = mass/volume).
3. Students are not expected to know that the atomic mass of a substance is a characteristic property.
4. They are not expected to know whether specific materials are or are not pure substances.
5. Because some properties do change with changing conditions (e.g., changing atmospheric pressure affects boiling point) all assessment items will make comparisons between substances where it is clear that the conditions, such as temperature and pressure, are constant.

Students are expected to know that:

1. When substances react chemically one or more new substances are formed.
2. If a new substance does not appear, a chemical reaction did not occur.
3. The products of a chemical reaction can be identified as new substances because each product has different characteristic properties from the original substances under the same conditions.
4. Liquids, solids, or gases can be reactants or products in chemical reactions.
5. It is possible for a single substance to undergo a chemical reaction, such as when the substance is heated or an electrical current flows through the substance.
6. It is not true that all chemical reactions are irreversible.

Boundaries:

1. Students are not expected to know that chemical reactions involve the rearrangement of atoms into new molecules. This idea is addressed in a later idea (Idea D).
2. Students are also not expected to know that nuclear reactions are not chemical reactions nor why nuclear reactions are not chemical reactions. Nuclear reactions are addressed in later ideas (4E/H6* and 4G/H6*)
3. By “predictable ways,” we mean that the same products will be formed when the same reactants are combined regardless of location and experimental set-up. Students are not expected to predict what the products of a reaction will be.
4. Students are expected to know that the original substances in a chemical reaction are called reactants and the resulting substances are called products but they will not be assessed on these definitions.

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.

Students are expected to know that:

1. When substances mix, undergo chemical reactions, change state, or dissolve, or when objects are cut or broken into smaller pieces, the total mass of all the matter will always remain the same.
2. Regardless of the form that the products of these processes may take (for example, when a sugar cube dissolves in water or a chemical reaction produces a gas), the mass will always stay the same.
3. If it appears that the mass has changed, it is because some material has not been accounted for.
4. Because light is not matter, its presence or absence does not affect the mass of the matter.

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.
2. Note: The words “weight,” “weigh,” and “mass” are used appropriately in the assessment items. The students are not expected to know the difference between “weight” and “mass.”

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.