Page 12 - Theory and Problems of BEGINNING CHEMISTRY

CHAPTER 1

Basic Concepts

1.1. INTRODUCTION
Chemistry is the study of matter and energy and the interactions between them. In this chapter, we learn about
the elements, which are the building blocks of every type of matter in the universe, the measurement of matter
(and energy) as mass, the properties by which the types of matter can be identified, and a basic classification of
matter. The symbols used to represent the elements are also presented, and an arrangement of the elements into
classes having similar properties, called a periodic table, is introduced. The periodic table is invaluable to the
chemist for many types of classification and understanding.
Scientists have gathered so much data that they must have some way of organizing information in a useful
form. Toward that end, scientific laws, hypotheses, and theories are used. These forms of generalization are
introduced in Sec. 1.7.

1.2. THE ELEMENTS
An element is a substance that cannot be broken down into simpler substances by ordinary means. A few
more than 100 elements and the many combinations of these elements—compounds or mixtures—account for
all the materials of the world. Exploration of the moon has provided direct evidence that the earth’s satellite is
composed of the same elements as those on earth. Indirect evidence, in the form of light received from the sun
and stars, confirms the fact that the same elements make up the entire universe. Before it was discovered on the
earth, helium (from the Greek helios, meaning “sun”) was discovered in the sun by the characteristic light it
emits.
It is apparent from the wide variety of different materials in the world that there are a great many ways to
combine elements. Changing one combination of elements to another is the chief interest of the chemist. It has
long been of interest to know the composition of the crust of the earth, the oceans, and the atmosphere, since
these are the only sources of raw materials for all the products that humans require. More recently, however,
attention has focused on the problem of what to do with the products humans have used and no longer desire.
Although elements can change combinations, they cannot be created or destroyed (except in nuclear reactions).
The iron in a piece of scrap steel might rust and be changed in form and appearance, but the quantity of iron
has not changed. Since there is a limited supply of available iron and since there is a limited capacity to dump
unwanted wastes, recycling such materials is extremely important.
The elements occur in widely varying quantities on the earth. The 10 most abundant elements make up 98%
of the mass of the crust of the earth. Many elements occur only in traces, and a few elements are synthetic.
Fortunately for humanity, the elements are not distributed uniformly throughout the earth. The distinct properties
of the different elements cause them to be concentrated more or less, making them more available as raw materials.
For example, sodium and chlorine form salt, which is concentrated in beds by being dissolved in bodies of water
that later dry up. Other natural processes are responsible for the distribution of the elements that now exists on
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