Chapter Ten: Matter and Temperature 10.1 The Nature of Matter 10.2 Temperature 10.3 The Phases of Matter

10.1 The Nature of Matter Matter anything that has mass and takes up space. Greek philosophers Democritus and Leucippus proposed that matter is made of tiny particles called atoms. The first evidence was called Brownian motion for Robert Brown, who first noticed the jerky motion of tiny particles.

10.1 Elements An element is a pure substance that cannot be broken down into another substance by chemical or physical means. For example, water can be broken down into its elements, hydrogen and oxygen, when energy is added.

10.1 Atoms atom is the smallest particle that retains the chemical identity of the element.

10.1 Atoms Carbon atoms are different from sodium, aluminum, or oxygen atoms. They have different masses.

10.1 Compounds and elements Compounds are two or more different elements chemically bonded together.

10.1 Examples of compounds Compounds contain more than one type of atom joined together.

10.1 Molecules A molecule is a group of two or more atoms joined together chemically.

10.1 Mixtures Many substances you encounter are a mixture of different elements and compounds. How many atoms are in this mixture? How many molecules are in this mixture?

10.1 Elements, compounds, and mixtures Can you distinguish between atoms and molecules in these images?

10.2 Temperature There are two common temperature scales. On the Fahrenheit scale, water freezes at 32 degrees and boils at 212 degrees. The Celsius scale divides the interval between the freezing and boiling points of water into 100 degrees.

Solving Problems A friend in Paris sends you a recipe for a cake. The French recipe says to bake the cake at a temperature of 200 °C for 45 minutes. At what temperature should you set your oven, which uses the Fahrenheit scale?

Looking for: Given: Relationships: Solution Solving Problems …temperature in degrees Fahrenheit Given: …temperature 200 C Relationships: TF = 9/5 TC + 32 Solution TF = (9/5)(200 °C) + 32 = 392 °F

10.2 What temperature really is Atoms are in constant motion, even in a solid object. The back-and-forth jiggling of atoms is caused by thermal energy, which is a kind of kinetic energy.

10.2 What temperature really is Temperature measures the kinetic energy per molecule due to random motion.

10.2 Thermometers A thermometer is an instrument that measures the exact temperature. Most thermometers contain either a silvery fluid (mercury) or a red fluid, which is alcohol containing a small amount of red dye.

10.2 How a thermometer works The volume of alcohol in a thermometer contains huge numbers of alcohol molecules. As temperature increases, the alcohol molecules move faster and bounce off each other. The liquid alcohol expands and takes up more space in the thermometer.

10.2 Measuring temperature A thermistor is a device that changes its electrical resistance as the temperature changes. Some digital thermometers sense temperature by measuring the resistance of electrons passing through wire.

10.2 Liquid-crystal thermometers Some thermometers contain liquid crystals that change color based on temperature. As temperature increases, the molecules of the liquid crystal bump into each other more and more. This causes a change in the structure of the crystals, which in turn affects their color.

10.2 Absolute zero Absolute zero is -273°C. You cannot have a temperature lower than absolute zero. Think of absolute zero as the temperature at which atoms are “frozen.”

10.2 Converting to Kelvin The Kelvin temperature scale is useful in science because it starts at absolute zero. To convert from Celsius to Kelvin, you add 273 to the temperature in Celsius.

10.3 Phases of Matter On Earth, pure substances are usually found as solids, liquids, or gases. These are called phases of matter.

10.3 The phases of matter A solid holds its shape and does not flow. The molecules in a solid vibrate in place, but on average, don’t move far from their places.

10.3 The phases of matter A liquid holds its volume, but does not hold its shape—it flows. Liquids flow because the molecules can move around.

10.3 The phases of matter A gas flows like a liquid, but can also expand or contract to fill a container. A gas does not hold its volume. The molecules in a gas have enough energy to completely break away from each other.

10.3 The phases of matter When they are close together, molecules are attracted through intermolecular forces.

10.3 The phases of matter The forces in chemical bonds are stronger than intermolecular forces.

10.3 Intermolecular forces

10.3 Intermolecular forces Within all matter, there is a constant competition between temperature and intermolecular forces. When temperature wins the competition, molecules fly apart and you have a gas. When intermolecular forces win the competition, molecules clump tightly together and you have a solid.

10.3 Melting and boiling The melting point is the temperature at which a substance changes from a solid to a liquid.

10.3 Melting and boiling The temperature at which a liquid becomes a gas is called the boiling point.

Notice temperature is constant while ice melts! As heat energy is added to ice, the temperature increases until it reaches 0°C. Then the temperature stops increasing. As you add more heat, more ice becomes liquid water but the temperature stays the same. This is because the added energy is being used to break the intermolecular forces and change solid into liquid. Once all the ice has become liquid, the temperature starts to rise again if more energy is added.

10.3 Melting and boiling points of common substances Materials have a wide range of melting and boiling points.

10.3 Sublimation Sometimes a solid can change directly to a gas when heat energy is added. This process is called sublimation.

10.3 Plasma In the plasma phase, matter becomes ionized as electrons are broken loose from atoms. The Sun is made of plasma, as is most of the universe, including the Orion nebula.