When trying to describe the quantity or quality of something, whether a chemical substance or physical
phenomenon, it is helpful to have some standard measure to refer to. A unit is nothing more than a standard by which a measured value can be described. For instance, in the old English system, a foot was just that--the length of a man's foot. This was helpful in that when a distance between, say, a house and a water well was described in feet, one who had never seen the dwelling in question would have an instant idea of how far away the well was, based solely on a verbal description. The concept today hasn't changed, although our standards make better scientific sense and are more exact.
Lesson 1. Early Ideas About the Atom
Matter is basically made up of atoms. This theory started more than 2,400 years ago
in Ancient Greece. But its rapid development only began about 1,000 years ago, when
John Dalton presented his own version of the atomic theory in 1803. In this lesson, we will
present the original Greek concept of the atom, and that of Dalton.
The Greek Concept
During the ancient times (around 440 B.C.), many of the “scientists” were
philosophers. They did not prove or disprove ideas using experiments. Rather, they used
good arguments to show that an idea was true. And so, Leucippus used logical reasoning to
Air is all around us. We breathe in the air so that our body can receive adequate
supply of oxygen gas. Our lungs expand as they fill with air and take in oxygen, and relax
as they release carbon dioxide. Plants in turn, use up the carbon dioxide during the process
of photosynthesis to manufacture sugars. Life as we know it would not have been possible
without the life-sustaining gases found in the atmosphere
Lesson 1. Kinetic Molecular Theory of Gases
The word “gas” seems to mean different things to
various people. Some think that it refers to the ‘gas’ that we
use for cooking and heating. Others think that ‘gas’ is the
fuel for automobiles and industrial machines.
So, what is meant by gas? Gas is found everywhere.
It enters our body everyday every time we inhale and exhale.
Do you know that almost 16 kg of gases get into our lungs
everyday? Every time we use perfume spray or aerosol
Lesson 1. What Distinguishes Solutions from Non-Solutions?
When you are preparing coffee in the morning, you are actually making a solution. It
is considered a solution because it is a homogenous mixture of two or more substances
evenly distributed in each other. The coffee and sugar that you mix in the hot water are the
solutes or the substances dissolved, and the solvent is the hot water, the liquid material in
Lesson 1. What is the Difference Between Osmotic Pressure and Vapor Pressure?
Before differentiating these two terminologies, let us first understand the difference
between the two classifications of solutions according to their properties – colligative and
non-colligative properties. Earlier, we have defined that colligative properties will just
Lesson 1. How Do You Classify Colloids?
Mixtures are classified as suspensions, colloids and solutions. By now, you should
clearly distinguish between suspensions and solutions (Module 15). The only new term to
you is just colloid. Let us check how well you can differentiate these three types of mixtures
Lesson 1. Defining Matter
Do you know that chairs, plates, air, wood, water, mud, sea and birds have one thing
in common? They are all classified as matter! So, what is matter? Can we say that all the
things around us are examples of matter? To answer these questions, let us perform
Lesson 1. Identifying Laboratory Apparatus and Its Uses
When you think of chemists at work, you probably imagine them in a modern
laboratory with test tubes, other delicate instruments, apparatus, and bottles of strange
You’re right! In the laboratory, you can find different laboratory apparatus. The
Science laboratory is a place of adventure and discovery. Some of the most exciting events
in scientific history have happened in the laboratory. The discovery of the atoms, the
production of plastics for clothing, the analysis of chemicals of substances, and other
The Origins of Chemistry: Where It All Began
The earliest attempts to explain natural phenomena led to fanciful inventions – to
myths and fantasies – but not to understanding.
Around 600 B.C., a group of Greek philosophers became dissatisfied with these
myths. Stimulated by social and cultural changes as well as curiosity, they began to ask
questions about the world around them. They were able to discover basic truths of nature
by thinking things through experiments. The years between 600 B.C. and 400 B.C. are
called the “Golden Age of Philosophy”.
Some of the Greek philosophers believed they could find a single substance from
A. History of the Periodic Table
The early years of the 19th century witnessed a rapid development in chemistry. The
art of distinguishing similarities and differences among atoms prompted scientists to devise
a way of arranging the elements. Relationships were discerned more readily among the
compounds than among the elements; thus, the classification of elements lagged many
years behind the classification of compounds. In fact, no general agreement had been
reached among chemists as to the classification of elements for nearly half a century after
the systems of classification of compounds had been established.
It was in 1817 when Johann Wolfgang Döbereiner showed that the atomic weight