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 is a term used to describe anything that has mass and takes up space.  Greek philosophers Democritus and Leucippus proposed that matter is made of tiny particles called atoms.  Atoms were an idea that few believed.  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 other substance by chemical or physical means.  All of the matter you are ever likely to experience is made from one or more elements in nature.

10.1 Elements  For example, water can be broken down into its elements, hydrogen and oxygen, when energy is added.

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

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.

 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? Solving Problems

1.Looking for:  …temperature in degrees Fahrenheit 2.Given:  …temperature 200  C 3.Relationships:  T F = 9/5 T C Solution  T F = (9/5)(200 °C) + 32 = 392 °F Solving Problems

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  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!

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.

12.1 Properties of Solids  Different kinds of matter have different characteristics.  Characteristics that can you observe directly are called physical properties.  Physical properties include color, texture, density, brittleness, and state (solid, liquid, or gas). Ex. Iron is solid at room temp.

12.1 Properties of Solids  A physical change is any change in the size, shape, or phase of matter in which the identity of a substance does not change.  For example, when water is frozen, it changes from a liquid to a solid.

12.1 Properties of Solids  Properties that can only be observed when one substance changes into a different substance are called chemical properties.  Any change that transforms one substance into a different substance is called a chemical change. Ex. If you leave a nail outside, it rusts.

17.1 Chemical Reactions  A chemical reaction is the process of breaking of chemical bonds in one or more substances, and the reforming of new bonds to create new substances.  When you make pizza, which changes are physical and which are chemical changes?

17.1 Evidence of chemical change Four indicators of chemical change are: 1.Formation of new gas 2.Formation of new solid 3.Release of energy (heat or light) 4.Color change