INTEGRATED PHYSICS AND CHEMISTRY – UNIT 1
PROPERTIES OF MATTER (1)
The man who came closest to our modern view of matter was Democritus, who lived about 460 B.C. He believed that all matter was composed of a large number of small objects which he called atoms (from a Greek word meaning indivisible ). Democritus believed these objects were in constant motion, and that they combined with each other in different shapes and sizes.
Another Greek philosopher, Aristotle, believed that all matter was composed of one or a combination of four things: earth, fire, air, and water. He disagreed with almost all of the ideas of Democritus.
The ideas put forth by Aristotle were so influential that theories of matter changed very little until 1808 when the scientist John Dalton developed new theories. Dalton performed experiments to help answer his questions, eventually developing the atomic theory. This theory states that all matter consists of extremely small particles--Democritus's atoms. Dalton determined that all atoms of any one element are similar to one another but are different from atoms of all other elements. Dalton also believed that atoms were indivisible, a hypothesis which has since been proven false.
Today, with the aid of the electron microscope and other modern technology, groups of atoms, called molecules , can be "seen." Models of particles even smaller than atoms have been developed. As you can see, throughout the centuries scientists have attempted to unravel the inner secrets of matter.
In this unit you will study some of the things scientists have discovered about matter and thus gain an ever greater appreciation for this magnificent universe.
The temperature scale with water freezing at 32° and boiling at 212°.
A chamber having a shape like a pipe.
The temperature scale with water freezing at 0º and boiling at 100º.
Having the properties of a straight line.
The mass of a substance per unit of volume.
Having the form of a cube.
Two or more atoms chemically combined.
The curved top surface of a liquid column.
Space occupied by an object or substance, measured in cubic units.
The metric system of units.
The amount of matter in an object.
The temperature scale with water freezing at 0° and boiling at 100°. Same as Celsius.
The smallest part of an element that can exist alone.
The tendency of an object to float in a fluid.
An instrument for determining mass.
To assign to a category.
Scientists study the world around us to learn how materials are alike and different. Some of the ways that kinds of matter differ are easy to see and some are not. Every kind of material has at least one property that makes it different from any other material. Why can glass be used for cookware but plastic usually cannot? Why do different objects of equal weight occupy different amounts of space? How can an object be changed from one kind of matter to another? What property explains rust on a piece of metal? These questions and others are answered by studying the properties of matter in the following lessons.
GENERAL PROPERTIES OF MATTER
How is all matter alike? Let us examine the two basic properties that all matter shares.
Volume. The first general property of matter is that it takes up space. No two units of matter can take up the same space at the same time. One unit must move. If you have ever dropped something into a full pail of water, you might have noticed that some of the water flowed over the edge of the pail. Whatever was dropped into the pail took up some of the space that had been filled by the water. As a result, some of the water was displaced from (pushed out of) the pail. Air can also push water out of one place and into another. The amount of space that matter takes up is called the volume of that matter. Thus, a giant boulder has more volume than a small rock. However, any unit of matter, large or small, solid, liquid, or gas, takes up some space and therefore has volume.
For an object of uniform shape having linear sides or a common geometric shape (for example, a block of wood, a brick, or a cylinder): Measure the object and determine the volume mathematically.
For an irregularly shaped object which cannot be measured easily or does not consist of uniform geometric shapes (for example, a horseshoe or a blob of silly putty): Determine the volume of water which it displaces. The volume of water displaced equals the volume of the object, as long as the object does not dissolve in or absorb water.
When measuring a volume of water in a graduated cylinder or similar container, be sure you are reading at the lowest point of the curved surface of the water, the meniscus. Study Figure 1 to find the correct level.
Mass. If you were to lift a small stick and a large rock, you could tell quickly which one was heavier. This experiment would tell you about another general property of matter. All matter on earth has weight. When you weigh something, you are measuring the pull of the earth's gravity on that object. Why do some things weigh more than others? The reason is that some things have more matter in them than others. The amount of matter in an object is called the mass of that object. Mass is measured in grams. The more mass an object has, the greater the force of gravity will be on it. As a result the object will weigh more. Keep in mind that the terms mass and weight are defined differently.
Remember that weight changes slightly with altitude or position on the earth. Weight on the moon is substantially different than weight on earth. The mass of an object, however, is constant--it doesn't change. Because the weight of an object is not constant, merely weighing an object will not allow you to determine its mass. The mass of an object is determined by placing it on a balance and comparing it with a known standard mass. The standard of mass is the kilogram (kg).
SPECIAL PROPERTIES OF MATTER
We know that all matter must possess mass and take up space. Yet, other properties can help us learn what makes each kind of substance different from the others.
Knowing the shape, odor, taste, color, density, buoyancy, freezing point, and boiling point of a material will tell us what the substance is like. These properties are called special properties. These special properties tell us a great deal about the ways a substance may react or be used. For example, you may have three beakers full of different liquids; one contains plain water, one contains grape soda, and one contains white vinegar. All three liquids have mass and take up space. How can we tell them apart? One way is to classify the three liquids according to their special properties. The soda can be distinguished from the other two by its color and taste. The water and the vinegar look the same but can be distinguished from each other by odor, taste, and boiling point.
We can also find out many of the special properties of a substance by looking at a table or chart that has this kind of information.
Knowing differences between one type of matter and another helps us classify things. Since all matter has mass and takes up space, the special properties are important for us to know.
Density. Density is an important special property of matter that needs further explanation. Density is the mass of a substance per unit of volume. In the metric system, volume is measured in liters, milliliters, or in the case of the figure to the right, cubic centimeters (cm3 ). It may be expressed in grams per cubic centimeter (g/cm3 ). For example, water has a density of 1 gram per cubic centimeter. If we compare a thousand grams of iron with a thousand grams of water, their masses are equal; but the container holding the water would be much larger than the one containing the piece of iron because the iron has a greater density.
Another way of looking at density is to compare cotton and lead. If you take two equal sized boxes and fill one with cotton and one with lead, you will see that the cotton and lead both occupy equal volumes. What do you think would happen when you try to lift the boxes? Which one would be heavier? Because the lead has more mass per box than the cotton does, you could conclude that the lead has greater density. Simply put, a given volume of lead contains more mass than does the same volume of cotton. To find the density of a substance, you must first know its mass and volume. Figure 2 lists densities of some common substances.
Note: This and other answers may be printed as 2g/cm3 . This format is used by some computers, printers, and calculators solely to keep the text on the same line.
Buoyancy. Why do some things float? You already know that heavy objects tend to sink, and light or hollow objects tend to float. Floating is related to density. Paper, cork, wood, and some plastics float on water. Each of these substances has a low density. A piece of steel will sink to the bottom. Yet, a merchant ship made of steel will float. Why?
When an object is placed into a liquid, it pushes that liquid aside. The object displaces the liquid. In other words, it moves the liquid to another place since both substances cannot occupy the same space at the same time. When you get into a filled bathtub, you probably notice that the water level rises. Your body is displacing or pushing aside a certain amount of water. If the mass of the amount of liquid displaced is equal to the mass that displaced it, the object will float. This law, or principle, is known as the Archimedes' Principle, named for Archimedes, the Greek philosopher who discovered it. When a block of wood is placed in water, it sinks until an amount of water exactly equal to the mass of the block is displaced. The water underneath the wood exerts a push or force to hold it up. This upward force is called buoyancy.
Freezing and boiling points. Temperatures of the boiling and freezing points of substances are special properties of matter. Different materials have different freezing and boiling points.
The freezing point is the temperature at which a liquid changes to a solid. The boiling point is the temperature at which a liquid changes to a gas. Because each substance has a unique freezing and boiling point, many unknown liquids are able to be identified by measuring their freezing and boiling points.
Measurements of freezing and boiling points are made using the Celsius temperature scale (Figure 3). Celsius temperature has been accepted around the world and has everyday use in many countries. The freezing point of water on the Celsius scale is 0°C. The boiling point is 100°C. The thermometer has one hundred degrees of temperature between the freezing and boiling points. The term centigrade is also used in referring to the Celsius scale. The Fahrenheit temperature scale is commonly used in many homes, but does not have the world-wide use that the Celsius has. The Fahrenheit scale is different in that water freezes at 32° and boils at 212°.
Stanley Explains the Celsius Scale (Click on the image above.)
CHEMICAL PROPERTIES OF MATTER
To understand fully the properties and nature of matter, we must look beyond the physical characteristics of matter. Some properties of matter depend upon the reactions of a substance with other substances. These properties are called chemical properties of a substance. Chemical reactions depend on how different substances combine with each other. If an element will not combine with any other substance it is said to be inert.
Simple Observations of Physical and Chemical Changes (Click on the image above.)
The souring of milk, the burning of a log, and the rusting of iron all involve reactions of substances resulting in changes in their chemical compositions. In rusting or burning a chemical process occurs when a substance combines with the oxygen in the air and a change takes place. These chemical processes are examples of oxidation, the result of combining a particular substance with oxygen. Rapid oxidation causes burning while instant oxidation causes an explosion.
Help Farmer Frank get off the ground by reviewing what you've learned.
