Matter, Energy, and Measurement

KEY QUESTIONS
1.1 Why Do We Call Chemistry
the Study of Matter?
1.2 What Is the Scientific
Method?
1.3 How Do Scientists Report
Numbers?
1.4 How Do We Make
Measurements?
1.5 What Is a Handy Way
to Convert from One
Unit to Another?
How To . . . Do Unit
Conversions by the
Factor-Label Method
1.6 What Are the States
of Matter?
1.7 What Are Density
and Specific Gravity?
1.8 How Do We Describe the
Various Forms of Energy?
1.9 How Do We Describe Heat
and the Ways in Which It
Is Transferred?
.1 Why Do We Call Chemistry the Study of Matter?
The world around us is made of chemicals. Our food, our clothing, the buildings
in which we live are all made of chemicals. Our bodies are made of
chemicals, too. To understand the human body, its diseases, and its cures,
we must know all we can about those chemicals. There was a time—only a
few hundred years ago—when physicians were powerless to treat many diseases.
Cancer, tuberculosis, smallpox, typhus, plague, and many other sicknesses
struck people seemingly at random. Doctors, who had no idea what
caused any of these diseases, could do little or nothing about them. Doctors
treated them with magic as well as by such measures as bleeding, laxatives,
hot plasters, and pills made from powdered stag horn, saffron, or gold. None
of these treatments was effective, and the doctors, because they came into
direct contact with highly contagious diseases, died at a much higher rate
than the general public.

1.2 What Is the Scientific Method?
Scientists learn by using a tool called the scientific method. The heart of
the scientific method is the testing of theories. It was not always so, however.
Before about 1600, philosophers often believed statements just
because they sounded right. For example, the great philosopher Aristotle
(384–322 BCE) believed that if you took the gold out of a mine it would grow
back. He believed this idea because it fitted in with a more general picture
that he had about the workings of nature. In ancient times, most thinkers
behaved in this way. If a statement sounded right, they believed it without
testing it.
About 1600 CE, the scientific method came into use. Let us look at an
example to see how the scientific method operates. The Greek physician
Galen (200–130 BCE) recognized that the blood on the left side of the heart
somehow gets to the right side. This is a fact. A fact is a statement based on
direct experience. It is a consistent and reproducible observation. Having
observed this fact, Galen then proposed a hypothesis to explain it. A
hypothesis is a statement that is proposed, without actual proof, to explain
the facts and their relationship. Because Galen could not actually see how
the blood got from the left side to the right side of the heart, he came up
with the hypothesis that tiny holes must be present in the muscular wall
that separates the two halves.
Up to this point, a modern scientist and an ancient philosopher would
behave the same way. Each would offer a hypothesis to explain the facts.
From this point on, however, their methods would differ. To Galen, his
explanation sounded right and that was enough to make him believe it,
even though he couldn’t see any holes. His hypothesis was, in fact, believed
by virtually all physicians for more than 1000 years. When we use the scientific
method, however, we do not believe a hypothesis just because it
sounds right. We test it, using the most rigorous testing we can imagine.

1.3 How Do Scientists Report Numbers?
Scientists often have to deal with numbers that are very large or very small.
For example, an ordinary copper penny (dating from before 1982, when pennies
in the United States were still made of copper) contains approximately
29,500,000,000,000,000,000,000 atoms of copper
and a single copper atom weighs
0.00000000000000000000000023 pound
which is equal to
0.000000000000000000000104 gram
Many years ago, an easy way to handle such large and small numbers was
devised. This method, which is called exponential notation, is based on
powers of 10. In exponential notation, the number of copper atoms in a
penny is written
2.95 1022
and the weight of a single copper atom is written
2.3 10225 pound
which is equal to
1.04 10222 grams
The origin of this shorthand form can be seen in the following examples:
100 1 10 10 1 102
1000 1 10 10 10 1 103
What we have just said in the form of an equation is “100 is a one with two
zeroes after the one, and 1000 is a one with three zeroes after the one.” We
can also write
1/100 1/10 1/10 1 1022
1/1000 1/10 1/10 1/10 1 1023
where negative exponents denote numbers less than 1. The exponent in a
very large or very small number lets us keep track of the number of zeros.
That number can become unwieldy with very large or very small quantities,
and it is easy to lose track of a zero. Exponential notation helps us deal with
this possible source of mathematical error.
When it comes to measurements, not all the numbers you can generate
in your calculator or computer are of equal importance. Only the number of
digits that are known with certainty are significant. Suppose that you measured
the weight of an object as 3.4 g on a balance that you can read to the
nearest 0.1 g. You can report the weight as 3.4 g but not as 3.40 or 3.400 g