5.1 The Particle Model of Matter 117 NEL More than 2000 years ago in Greece, a philosopher named Democritus suggested that matter is made up of tiny particles too small t o be seen. He thou ght that if you k ept cutt ing a substa nce into smaller and smaller pieces, you wou ld eventually come to the smallest possible particles—the building blocks of matter . Many years lat er, scientists came back to Democritus’ idea and added to it. The theory they developed is called the of mat ter . There are four main ideas in the particle model: 1. All mat ter is made u p of tin y p articles. particle model The Particle Model of Matter5. 1 5. 1 Scientists find the p article model useful for two reasons. First, it provides a reasonable explanation for t he behaviour of matter . Second, it presen ts a very important ide a—the pa rticles of matt er are alway s moving. Matter that seems perfectly motionless is not motio nless at al l. The a ir y ou br eathe, you r boo ks, you r des k, and even your bod y all consist o f particles that are in co nstant motion. Thus, the particle model can be used t o explain the pro perties ofsolids, liquid s, and gase s. It can also be used to exp lain what happe ns in ch anges of stat e (Figure 1 on the next page). heat 2. The particle s of mat ter are alway s mo ving. 3. The parti cle s hav e spac es bet wee n them. 4. Add ing heat t o matt er mak es the part icles mo ve fast er. LEARNING TIP Are you able to explain the particle model of matter in your own words? If not, re-read the main ideas and examine the illustration that goes with each.
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