Alaska Science
Key Element A2

A student who meets the content standard should understand the physical, chemical, and nuclear changes and interactions that result in observable changes in the properties of matter (Changes and Interactions of Matter).

Performance Standard Level 3, Ages 11–14

Students will explain changes that occur in physical and chemical properties of matter using a qualitative description of changes on a molecular level, including conservation of matter.

Sample Assessment Ideas

• Students identify the characteristics of matter that go into a campfire (logs, sticks, fuel, oxygen); observe the characteristics of the final matter (ashes, smoke, carbon dioxide); use chemical symbols and models to write the equation and demonstrate conservation of atoms for a simple combustion reaction of natural gas (CH4 methane).

• Students predict and explain the flexibility, expansion or contraction of materials (such as snow machine tracks, sled runners, windshield materials, or mercury in a thermometer) under different extreme temperature conditions.

Standards Cross-References
( Alaska Department of Education & Early Development Standards)

National Science Education Standards

A substance has characteristic properties, such as density, a boiling point, and solubility, all of which are independent of the amount of the sample. A mixture of substances often can be separated into the original substances using one or more of the characteristic properties. (Page 154)

Substances react chemically in characteristic ways with other substances to form new substances (compounds) with different characteristic properties. In chemical reactions, the total mass is conserved. Substances often are placed in categories or groups if they react in similar ways; metals is an example of such a group. (Page 154)

Chemical elements do not break down during normal laboratory reactions involving such treatments as heating, exposure to electric current, or reaction with acids. There are more than 100 known elements that combine in a multitude of ways to produce compounds, which account for the living and nonliving substances that we encounter. (Page 154)

Benchmarks

Atoms and molecules are perpetually in motion. Increased temperature means greater average energy of motion, so most substances expand when heated. In solids, the atoms are closely locked in position and can only vibrate. In liquids, the atoms or molecules have higher energy of motion, are more loosely connected, and can slide past one another; some molecules may get enough energy to escape into a gas. In gases, the atoms or molecules have still more energy of motion and are free of one another except during occasional collisions. (Page 78)

The temperature and acidity of a solution influence reaction rates. Many substances dissolve in water, which may greatly facilitate reactions between them. (Page 78)

Scientific ideas about elements were borrowed from some Greek philosophers of 2000 years earlier, who believed that everything was made from four basic substance: air, earth, fire, and water. It was the combinations of these “elements” in different proportions that gave other substances their observable properties. The Greeks were wrong about those four, but now over 100 different elements have been identified, some rare and some plentiful, out of which everything is made. Because most elements tend to combine with others, few elements are found in their pure form. (Page 78)

There are groups of elements that have similar properties, including highly reactive metals, less reactive metals, highly reactive nonmetals (such as chlorine, fluorine, and oxygen), and some almost completely nonreactive gases (such as helium and neon). An especially important kind of reaction between substances involves combinations of oxygen with something else—as in burning or rusting. Some elements don’t fit into any of the categories; among them are carbon and hydrogen, essential elements of living matter. (Page 78)

No matter how substances within a closed system interact with one another, or how they combine or break apart, the total weight of the system remains the same. The idea of atoms explains the conservation of matter: if the number of atoms stays the same no matter how they are rearranged, then their total mass stays the same. (Page 79)