Chemistry is too universal and dynamically-changing a subject to be
confined to a fixed definition; it might be better to think of chemistry
more as a point of view that places its major focus on the structure and properties of substances— particular kinds of matter— and especially on the changes that they undergo. In some ways, physics
might be considered more "fundamental" to the extent that it deals with
matter and energy in a more general way, without the emphasis on
particular substances. But the distincion can get pretty fuzzy; it is
ultimately rather futile to confine any aspect of human endeavour to
little boxes.
Chemistry: the central science
The
real importance of Chemistry is that it serves as the interface to
practically all of the other sciences, as well as to many other areas of
human endeavor. For this reason, Chemistry is often said (at least by
chemists!) to be the "central science".
Chemistry can be "central" in a much more personal way: with a solid
background in Chemistry, you will find it far easier to migrate into
other fields as your interests develop.
Chemistry can enhance any career.
Chemistry is so deeply ingrained into so many areas of business,
government, and environmental management that some background in the
subject can be useful (and able to give you a career edge as a team
member having special skills) in fields as varied as product
development, marketing, management, computer science, technical writing,
and even law.
So just what is chemistry?
Do you remember the story
about the group of blind men who encountered an elephant? Each one
moved his hands over a different part of the elephant's body— the trunk,
an ear, or a leg— and came up with an entirely different description of
the beast.
Chemistry can similarly be approached in different ways, each
yielding a different, valid, (and yet hopelessly incomplete) view of the
subject.
Thus we can view chemistry from multiple standpoints ranging from the theoretical to the eminently practical:
Mainly theoretical
Mainly practical
Why do particular combinations of atoms hold together, but not others?
What are the properties of a certain compound?
How can I predict the shape of a molecule?
How can I prepare a certain compound?
Why are some reactions slow, while others occur rapidly?
Does a certain reaction proceed to completion?
Is a certain reaction possible?
How can I determine the composition of an unknown substance?
Boiling it down to the basics
At the most fundmental level, chemistry can be organized along the lines shown here.
Dynamics
refers to the details of that
rearrangements of atoms that occur during chemical change, and that
strongly affect the rate at which change occurs.
Energetics
refers to the thermodynamics of chemical change, relating
to the uptake or release of heat. More importantly, this aspect of
chemistry controls the direction in which change occurs, and the mixture
of substances that results.
Composition and structure
define the substances that are results of chemical change. Structure
refers specifically to the relative arrangements of the atoms in space.
The extent to which a given structure can persist is itself determined
by energetics and dynamics.
Synthesis
strictly speaking, refers to formation of new (and usually
more complex) substances from simpler ones, but in the present context
we use it in the more general sense to denote the operations required to
bring about chemical change and to isolate the desired products.
This view of Chemistry is a rather astringent one that is probably
more appreciated by people who already know the subject than by those
who are about to learn it, so we will use a somewhat expanded scheme to
organize the fundamental concepts of chemical science. But if you need a
single-sentence"definition of Chemistry, this one wraps it up pretty
well:
Chemistry is the study of substances; their properties, structure, and the changes they undergo.
Micro-macro: the forest or the trees
Chemistry, like all the natural sciences, begins with the direct
observation of nature— in this case, of matter. But when we look at
matter in bulk, we see only the "forest", not the "trees"— the atoms and
molecules of which matter is composed— whose properties ultimately
determine the nature and behavior of the matter we are looking at.
This dichotomy between what we can and cannot directly see
constitutes two contrasting views which run through all of chemistry,
which we call macroscopic and microscopic.
In the context of Chemistry, "microscopic" implies detail at the
atomic or subatomic levels which cannot be seen directly (even with a
microscope!)
The macroscopic world is the one we can know by direct observations of physical properties such as mass, volume, etc.
The following table provides a conceptual overview of Chemical
science according to the macroscopic/microscopic dichotomy we have been
discussing. It is of course only one of many ways of looking at the
subject, but you may find it a helpful means of organizing the many
facts and ideas you will encounter in your study of Chemistry. We will
organize the discussion in this lesson along similar lines.
The
real importance of Chemistry is that it serves as the interface to
practically all of the other sciences, as well as to many other areas of
human endeavor. For this reason, Chemistry is often said (at least by
chemists!) to be the "central science". 
Do you remember the story
about the group of blind men who encountered an elephant? Each one
moved his hands over a different part of the elephant's body— the trunk,
an ear, or a leg— and came up with an entirely different description of
the beast.
Chemistry can similarly be approached in different ways, each
yielding a different, valid, (and yet hopelessly incomplete) view of the
subject.
At the most fundmental level, chemistry can be organized along the lines shown here. 