Essentials of Ecology

CONCEPT 2-3 39

Matter Occurs in Various

Physical Forms

The atoms, ions, and molecules that make up matter

are found in three physical states: solid, liquid, and gas.

For example, water exists as ice, liquid water, or wa-

ter vapor depending on its temperature and the sur-

rounding air pressure. The three physical states of any

sample of matter differ in the spacing and orderliness

of its atoms, ions, or molecules. A solid has the most

compact and orderly arrangement, and a gas the least

compact and orderly arrangement. Liquids are some-

where in between.

Some Forms of Matter Are

More Useful than Others

Matter quality is a measure of how useful a form of

matter is to humans as a resource, based on its availabil-

ity and concentration, or amount of it that is contained

in a given area or volume. High-quality matter is

highly concentrated, is typically found near the earth’s

surface, and has great potential for use as a resource.

Low-quality matter is not highly concentrated, is often

located deep underground or dispersed in the ocean or

atmosphere, and usually has little potential for use as a

resource. See Figure 2-6 for examples illustrating dif-

ferences in matter quality.

High Quality Low Quality

Salt

Coal

Gasoline

Aluminum can

Solution of salt in water

Coal-fired power

plant emissions

Automobile emissions

Aluminum ore

Solid Gas

Figure 2-6 Examples of differences in matter quality. High-quality

matter (left column) is fairly easy to extract and is highly concentrated;

low-quality matter (right column) is not highly concentrated and is more

difficult to extract than high-quality matter.

2-3 How Can Matter Change?

CONCEPT 2-3 When matter undergoes a physical or chemical change, no atoms are

created or destroyed (the law of conservation of matter).

▲

Matter Undergoes Physical,

Chemical, and Nuclear Changes

When a sample of matter undergoes a physical

change, its chemical composition, or the arrangement of

its atoms or ions within molecules does not change.

A piece of aluminum foil cut into small pieces is still

aluminum foil. When solid water (ice) melts or liquid

water boils, none of the H 2 O molecules are changed.

The molecules are simply arranged in different spatial

(physical) patterns.

THINKING ABOUT

Controlled Experiments and Physical Changes

How would you set up a controlled experiment

(Core Case Study) to verify that when water changes

from one physical state to another, its chemical composition

does not change?