Gases
If you were asked to name a gas, what would you say? Air, which is a mixture of gases, is probably the most obvious example. You might also mention natural gas, which is used as a fuel for heating homes. Gas is the state of matter in which a material has neither a definite shape nor a definite volume. (The adjective form of the word gas is gaseous (gas e us), as in gaseous state.) A gas takes the shapeand volume of its container.
The balloons in Figure 4 are filled with helium, a colorless gas that is less dense than air. Two of the balloons are teardrop-shaped and two are disk-shaped. The “shape” of the helium in a balloon is the same as the shape of the balloon itself. The volume of the helium in a balloon is equal to the volume of the balloon.
The helium atoms in a balloon are not arranged in a regular pattern, as shown in the drawing in Figure 4. They are at random locations throughout the balloon. There is more space between two helium atoms in a balloon than between two neighboring atoms in solid copper or liquid mercury.
Because of the space among helium atoms, a large amount of helium can be compressed into a metal cylinder. When helium flows from the cylinder into a balloon, the helium atoms spread out. If 200 balloons are filled from a single cylinder, the total volume of the balloons will be much larger than the volume of the cylinder.
Figure 4 Helium gas takes the volume and shape of its container. Observing Describe the shape of the helium in the blue balloon.
Other States of Matter
On Earth, almost all matter exists in a solid, liquid, or gaseous state. But ninety-nine percent of all the matter that can be observed in the universe exists in a state that is not as common on Earth. At extremely high temperatures, such as those found on the sun or other stars, matter exists as plasma. You will read more about the properties of plasmas in Chapter 10.
In the 1920s Satyendra Bose, a physicist from India, wrote a paper about the behavior of light. After Albert Einstein read the paper, he realized that the behavior described could apply to matter under certain conditions. Einstein made a bold prediction. He predicted that a fifth state of matter would exist at extremely low temperatures. At temperatures near —273°C, groups of atoms would behave as though they were a single particle. In 1995, scientists produced this fifth state of matter, which is called a Bose-Einstein condensate (or BEC). It behaved as Einstein had predicted decades before.
How can atoms behave at temperatures near ‒273°C?
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