Chapter 11: The Molecular Model of Matter

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The Continuous Model of matter represents matter as smooth and infinitely subdividable. It reflects well what appears to our naked eye, but it lacks explanatory power...many things remain a mystery as long as we view matter as continuous, smooth, and infinitely subdividable. The Molecular Model: Matter is composed of tiny particles called . Each kind of matter has a different kind of . Molecules of matter are in constant . Molecules move and interact in accord with the of motion and of force and conservation. Brownian Motion (dating from 1827) is evidence for the existence of . One sees Brownian Motion when one looks through a microscope at fine particles of dust suspended in water or fine particles of smoke suspended in air. The particles are seen to jitter about in a random fashion. The jittery motion is caused by the collisions of molecules (invisible, even to the microscope) with the visible particles of dust or smoke. The Molecular Model is simple and, once adopted, explains many things, but the molecules it postulates are extremely small and beyond the reach of the naked eye as well as all except the most modern and powerful microscopes. The Molecular Model explains the physical states of matter. In solids, the molecules move but still maintain relative positions. As kinetic energy is added to the molecules, they become more free to move relative to one another and a is formed. If given sufficient energy, the molecules can escape from one another and form a . If given yet more energy, the molecules may collide violently and be reduced to charged pieces, i.e., a . The Molecular Model explains "internal energy." Internal energy can be potential energy or energy of molecules. "Temperature" is a measure of the average energy of a collection of molecules. The Molecular Model explains how temperature is measured. Kinetic energy of the molecules of the measured substance is transmitted by collisions to the molecules of the thermometer. The Molecular Model explains why there is an absolute zero of temperature. When all of the energy of the molecules has been removed that can be removed, the temperature can go no lower. The Molecular Model explains why ice freezes at a constant temperature and why water boils at a constant temperature. When matter changes from one state to another, there is a rearrangement of the molecules which changes their energy but not their energy. The Molecular Model explains (one reason) why it gets warmer when it snows. When water vapor changes to solid (freezing), the water gives up electrical potential energy which becomes energy of the surrounding air molecules, warming it. The Molecular Model explains why evaporation cools a moist finger. When molecules escape from the moisture on the skin, it is the molecules with the (least, most?) kinetic energy that escape, thus reducing the average kinetic energy (temperature) of the molecules that remain behind. The Molecular Model explains "heat conduction." Kinetic energy of molecules in the hot object is given to the molecules of the cold object when the molecules collide with each other. The Molecular Model explains how gases exert pressure on a wall. Molecules exert forces when they the wall. The Molecular Model explain why pressure increases when temperature increases. The molecules at higher temperature have greater and exert greater forces on the wall when they collide. The Molecular Model makes plausible Avogadro's Hypothesis: "Equal numbers of molecules at the same temperature would exert the same pressure no matter what the of the molecules might be."

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