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Chemistry: Introduction and History
Perhaps Witch Doctors
and Alchemist are the predecessors to our modern chemist today. Any way you look at it, chemists
have been around for a long time.
One of the first was the Greek philosopher Democritus
who lived about 400 B.C.
Democritus believed that one could take a clod of soil and break it
into smaller pieces and that those pieces could in turn be broken into
even smaller pieces. But
eventually Democritus believed that you would finally have something that
was too small to be cut into any smaller pieces, which he referred to as
“atomos” (which means indivisible).
Scientists are still talking about atoms today, 2400 years after
Democritus. Chemistry to people is
much like a fish surrounded by water. The fish doesn’t realize that it
is surrounded by water just as most people do not realize they are
surrounded by chemistry. The
following links will give you some information concerning early chemistry
as well as some of the early chemist that have helped shape our knowledge
of chemistry to what it is today. LINKS: Measurements and Calculation
Measurement is
essential to chemists. In
fact, modern chemistry could have thought to have started when scientist
started going out weighting things.
It makes since that any measurements taken should be reported as
accurately and precisely as possible, this is where significant figures
comes into play. Different
text and different teachers treat significant figures differently. The links below should aid
you in studying significant figures, scientific notation and the metric
system. Significant
Figures and Rounding Metric
System/Conversion Factors
Scientific Method
The measurements and
calculations chemists use are often used to prove or disprove a scientific
theory. These theories are
formulated using the scientific method. The scientific method is simply a
systematic way for conducting research. Read the link below to find out
more. Matter and Energy
The age-old definition
of matter is whatever occupies space and has mass. Chemists usually divide matter
into three large groups; solids, liquids, and gases. The main difference in these three
is the amount of empty space between the molecules. In solids there is about 50% empty
space. In liquids, there is
60-80% empty space and in solids there is 99.9% empty space between the
molecules! This amount of
empty space drastically affects the properties of each making them very
different from one another.
It takes energy to move matter. Scientist break energy up into two
categories; kinetic and potential.
A body has kinetic energy because of it’s motion and potential
energy because of it’s position.
The link below gives a brief review of matter and energy. Atomic Theory and Structure
Since the time of
Democritus, the idea of atoms has come in and out of favor over the
years. Democritus only had
one kind of atom.
Interestingly, he thought atoms had different shapes. Democritus thought iron atoms
where shaped like cork screws because iron is a strong lightweight
metal. He theorized that the
atoms being shaped like cork screws would not pack very well and the atoms
would get tangled with one another.
Much like having a box of corkscrews. The box would be light, because
you can’t pack very many in there and you would not be able to put your
hand through the corkscrews to the bottom of the box because they would be
tangled. Lead on the other
hand, being very soft yet dense, Democritus felt that lead atoms would be
spherical, like billiard balls.
You can pack many billiard balls in a box making it very heavy yet
you can still stick your hand through the billiard balls and touch the
bottom because the balls slide off one another. In Democritus day, there where
only a few different elements known.
By the time Lavoisier came around in the mid 1700’s there were
about 20 elements known to man.
In the early 1800’s there were 50 or so elements known to man but
scientist really didn’t understand what atoms were or what made up an
atom. About this time John
Dalton proposed what is called “Dalton’s Modern Atomic Theory”. Although the theory has had to be
modified over the years, the basics still hold today. Today there are about 118
different elements known to man.
Scientists have come a long way over the last couple of hundred
years in identifying atoms and understanding what makes up an atom. Scientists know now that atoms are
made up of very small subatomic particles called electrons, protons and
neutrons. For more
information follow the links below. Chronological
order of elements Nomenclature
Of the more than 10
million compounds known today, each compound must have it’s own individual
name. Naming of compounds can
be very simple or very complicated, depending on the molecule in
question. The rules for
naming compounds are given by the International Union of Pure and Applied Chemistry
(IUPAC). To see IUPAC’s home
page, click here. For most freshman chemistry
students, nomenclature is limited to simple inorganic compounds. For some help with naming, try the
following links. Chemical Reactions and
Equations
A chemical equation
simply represents a chemical reaction in terms of symbols. Much information may be given in a
chemical equation. The
equation will tell what the reactants and products are in the
reaction. It may give
additional information concerning time, temperature, solvents, or other
conditions necessary for the reaction to occur. Part of the chemist job after
determining reactants and products is to balance the chemical
equation. Because of the The
Law of Conservation of Mass the number and kind of atoms must be the
same in the products as there are in the reactants. There are many different types of
chemical reactions that can occur.
A few of the more common types are decomposition, combination,
single and double displacement, synthesis and combustion. The links below will help you in
learning more about reactions and equations. Quantitative Chemistry and
Stoichiometry
Let’s say we want to
perform a chemical reaction.
We take a little bit of this with a little bit of that and mix it
all up. How do we know how
much is a “little bit”? Atoms
are very, very small. An atom
is so small; the number of atoms in a teaspoon of water is more teaspoons
of water than are in the Atlantic Ocean. So, counting atoms is out of the
question. What do we do? We count them by weighing
them. This practice is not
something you’re unfamiliar with.
If you go to the grocery store, how do you buy peanuts? By the pound of course because it
would be too much trouble to count them. Same thing with roofing tacks, we
by them by the pound because they are too small to count. Once we learn we can count atoms by
weighing them, we can put our reactants together in the proper ratios.
This is where the concept of the mole comes into
play. The mole is sometimes
referred to as the “chemists dozen” because it represents a certain
number, just as the dozen represents twelve. The mole, however, is much larger
than a dozen. The mole
represents 6.022 x 1023, a tremendously large number. By weighing our reactants and
determining the number of moles present we can then perform a chemical
reaction using the proper molar ratios. Chemical Bonding
When a person looks at
a periodic table, he or she certainly thinks about chemistry. Although the chemistry of the
individual elements is interesting in its own right, the real chemistry is
behind the infinite number of molecules that can be built from those
elements. How do they come together and how are the held together and what
are the shapes of the molecules?
There are two dominant bonding modes, covalent and ionic. Ionic bonds are strong
electrostatic attractions between ions of opposite charge. Covalent bonds are bonds that
result from the sharing of electron pairs between atoms. The ionic bonds are generally
formed between metals and nonmetals.
Covalent bonds are usually founds between nonmetals bonded
together. There are several
concepts available to students to answer questions like those above and to
help them understand the glue that holds these molecules together. Gases
Between solids,
liquids, and gases, gases are the most easily studied of the three. Nearly all gases behave the
same. This means you don’t
have to learn something for methane and something else for butane or
hydrogen cyanide. There are
sets of laws, referred to as “The Gas Laws” that can be applied to any
gas. Dalton’s Law of Partial
Pressure and The Ideal Gas Law are also important laws when it comes to
gases. The links below will
give you more information on these gas laws and how they are applied. Liquids and Solids
Liquids and solids
have quite different properties than those of gases. Gaseous molecules are unaware of
each other. That is, there
are no attractive force between gas molecules under normal conditions of
temperature and pressure. The
forces that hold liquid and solid molecules together are sufficiently
strong to hold the molecules into a solid or liquid state. The forces are mostly electrical
in nature and some are stronger than others. Properties
of Solids and Liquids Colligative
Properties of Solutions with Problems Solutions
Most of the time when
a chemist performs a reaction, the reaction is done in solution. A solution consists of a solvent
(that which does the dissolving) and a solute (that which gets
dissolved). Many times a
person thinks of a solution as a liquid solution, which many times is the
case. However, a solution can
be a solid, liquid, or gas.
It’s important to understand if a reaction is to be run in
solution, there must be a way to describe the concentration of the
solution so the molar ratios can be mixed in the proper amounts. A few of the more common methods
of describing concentrations of solutions include molarity, molality,
normality,
weight
percent, volume
percent, weight/volume
percent and mole
fraction. Molarity,
Molality, and Normality Practice
Molarity Calculations Acids and Bases
The idea of acids and
bases has been around for a long time. One of the first scientists to
categorize these into groups was Antoine Lavoisier. Lavoisier thought the chemical
properties of acids came from oxygen. Today we realize he was wrong but
nonetheless, it was a start.
The reason acids and bases are grouped into such large categories
is because they have certain properties in common. Acids for example, have a tart or
sour taste. If you’ve ever
bitten into a lemon, you’ve tasted citric acid. Acids will turn blue litmus paper
red and acids react with bases to destroy the chemical properties of the
base. Bases usually have a
bitter taste. Many of the
medicines we take are bases and that is why they taste bad. Bases will turn red litmus paper
blue and will react with acids to destroy the acid’s chemical
properties. The modern
definition of acids and bases is called the Bronsted/Lowry
Acid Base definition. The
theory was named after two scientists who independently of each other came
up with the same theory about acids and bases. Two other theories used are the Lewis
Acid Base Definition and the Arrhenius
Definition. Oxidation and Reduction
Oxidation/Reduction
(REDOX) reactions play a major role in nearly everything we touch. REDOX reactions occur in the
batteries we use in our calculators, flashlights, and cars. The reason galvanized nails
protect a nail from rusting and bars of zinc attached to naval ship hulls
cathodically protects the hulls from rusting is because of REDOX
reactions. Once we eat food,
very complicated REDOX reactions occur in our bodies that convert the food
to energy. The heart of REDOX
is electron transfer. The
substance being oxidized gives up electron(s) and the substance being
reduced gains the electron(s).
If oxidation takes place there will be an increase in oxidation
number where as in reduction, there is a decrease in oxidation
number. The key to
understanding REDOX reactions is to understand why one element is more
likely to give up it’s electrons whereas another element is more likely to
gain electrons. Reduction and Oxidation
Reactions Periodic Table
One of the most
valuable tools available to the chemist is the periodic table. The periodic table has undergone
some changes over the years but without it, the chemist would be like a
carpenter without his hammer.
The table of elements is arranged in such a way that we can often
predict how something is going to react or not react, what color the
compound is going to be and a wealth of other chemical and physical
properties just based upon the position of the element on the table. Countless hours of experiments and
research have gone into arranging the elements on the table in a
particular way. The links
below will give you some idea about how the periodic table came to be as
well as specific information about the elements on the table. Other Useful Links
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Any opinions, findings, and conclusions or
recommendations expressed in this material are those of the author(s) and do
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