National Science and Education Standards
In grades 5-8, students observe and measure characteristic properties, such as boiling points, melting points, solubility and simple chemical changes of pure substances. They use those properties to distinguish and separate one substance from another.
... It can be tempting to introduce atoms and molecules or to improve students' understanding of them so that particles can be used as an explanation for the properties of elements and compounds. However, use of such terminology is premature for these students and can distract from the understanding that can be gained from focusing on the observation and description of macroscopic features of substances and of physical and chemical reactions.
Properties and changes of properties in matter
Earth and Space Science
- 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.
A major goal of science in the middle grades is that students develop an understanding of Earth and the solar system as a set of closely coupled systems. The idea of systems provides a framework in which students can investigate the four major interacting components of the Earth system -- geosphere (crust, mantle and core), hydrosphere (water), atmosphere (air), and the biosphere (the realm of all living things). In this holistic approach to studying the planet, physical, chemical and biological processes act within and among the four components on a wide range of time scales to change continuously Earth's crust, oceans, atmosphere and living organisms. Students can investigate the water and rock cycles as introductory examples of geophysical and geochemical cycles. Their study of Earth's history provides some evidence about co-evolution of the planet's main features -- the distribution of land and sea, features of the crust, the composition of the atmosphere, global climate and populations of living organisms in the biosphere.
Structure of Earth System
- Water, which covers the majority of Earth's surface, circulates through the crust, oceans and atmosphere in what is known as the "water cycle." Water evaporates from Earth's surface, rises and cools as it moves to higher elevations, condenses as rain or snow, and falls to the surface where it collects in lakes, oceans, soil, and underground rocks.
- The atmosphere is a mixture of nitrogen, oxygen and trace gases that include water vapor. The atmosphere has different properties at different elevations.
- Clouds, formed by the condensation of water vapor, affect weather and climate.
- Global patterns of atmospheric movement influence local weather. Oceans have a major effect on climate, because water in the oceans retains a large amount of heat.
High-school students develop the ability to relate the macroscopic properties of substances that they study in grades K-8 to the microscopic structure of substances. This development in understanding requires students to move among three domains of thought -- the macroscopic world of observable phenomena, the microscopic world of molecules, atoms and subatomic particles; and the symbolic and mathematical world of chemical formulas, equations and symbols. The relationship between properties of matter and its structure continues as a major component of study in 9-12 physical science.
Structures and Properties of Matter
Earth and Space Science
Energy in the Earth System
- Bonds between atoms are created when electrons are paired up by being transferred or shared. A substance composed of a single kind of atom is called an element. The atoms may be bonded together into molecules or crystalline solids. A compound is formed when two or more kinds of atoms bind together chemically.
- The physical properties of compounds reflect the nature of the interactions among its molecules. These interactions are determined by the structure of the molecule, including the constituent atoms and the distances and angles between them.
- Solids, liquids and gases differ in the distances and angles between molecules or atoms and, therefore, the energy that binds them together. In solids, the structure is nearly rigid; in liquids, molecules or atoms move around each other but do not move apart; and in gases, molecules or atoms move almost independently of each other and are mostly far apart.
Project 2061 Benchmarks
The Physical Setting (6-8)
- Global climate is determined by energy transfer from the sun at and near Earth's surface. This energy transfer is influenced by dynamic processes such as cloud cover and Earth's rotation, and by static conditions such as the position of mountain ranges and oceans.
The Earth (4B) -- Students can now consolidate their prior knowledge of the Earth (as a planet) by adding more details (especially about climate), getting a firmer grasp of the geometry involved in explaining the seasons and phases of the moon, improving their ability to handle scale, and shifting their frame of reference away from the Earth when needed.
The cause of the seasons is a subtle combination of global and orbital geometry and of the effects of radiation at different angles. Students can learn part of the story at this grade level, but a complete picture cannot be expected until later.
- Because the Earth turns daily on an axis that is tilted relative to the plane of the Earth's yearly orbit around the sun, sunlight falls more intensely on different parts of the Earth during the year. The difference in heating of the Earth's surface produces the planet's seasons and weather patterns.
- The cycling of water in and out of the atmosphere plays an important role in determining climatic patterns. Water evaporates from the surface of the Earth, rises and cools, condenses into rain or snow, and falls again to the surface. The water falling on land collects in rivers and lakes, and in soil and porous layers of rock. Much of it flows back into the ocean.
The Structure of Matter (4D)
Common Themes (6-8)
Details of the structure of the atom need not be taught at this level. Students should become familiar with characteristics of different states of matter-now including gases-and transitions between them.
- Atoms and molecules are perpetually in motion. Increased temperature means greater average energy, 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, 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 and are free of one another except during occasional collisions.
Systems (11A) -- One of the essential components of higher-order thinking is the ability to think about a whole in terms of its parts and, alternatively, about parts in terms of how they relate to one another and to the whole. … Children tend to think of the properties of a system as belonging to individual parts of it, rather than as arising from the interaction of the parts.
The Physical Setting (9-12)
- A system can include processes as well as things.
- Thinking about things as systems means looking for how every part relates to others. The output from one part of a system (which can include material, energy or information) can become the input to other parts. Such feedback can serve to control what goes on in the system as a whole.
- Any system is usually connected to other systems, both internally and externally. Thus, a system may be thought of as containing subsystems and as being a subsystem of a larger system.
The Earth (4B)
- Weather, in the short run, and climate, in the long run, involve the transfer of energy in and out of the atmosphere. Solar radiation heats the land masses, oceans and air. Transfer of heat energy at the boundaries between the atmosphere, the land masses, and the oceans results in layers of different temperatures and densities in both the ocean and atmosphere. The action of gravitational force on regions of different densities causes them to rise or fall -- and such circulation, influenced by the rotation of Earth, produces winds and ocean currents.
The Structure of Matter (4D)
- Atoms often join with one another in various combinations in distinct molecules or in repeating three-dimensional crystal patterns. An enormous variety of biological, chemical and physical phenomena can be explained by changes in the arrangement and motion of atoms and molecules.