|
Introduction
All
substances around us consist of matter. Matter is the material mass that
makes up the substance. The
blackboard in the classroom, the chair that you are sitting on, the air you
breathe, the food you eat, the plate and spoon, etc. are all made up of
matter. To say it more grandiosely, everything in the Universe is made up of
matter.
Substances
exist in various forms or states. They
can be solids, liquids or gaseous. They can also exist in pure form or in
combinations. We shall study some of these aspects in this chapter.
What
we will study in this chapter
:
1.
Definitions of elements, compounds and mixtures
2. States of matter
1.
Elements, Compounds and Mixtures
A question that might spring to your
mind is what is matter? If you take a piece of chalk and go on cutting it
into smaller and smaller bits, you will come to a stage where you will need
a microscope to see the smaller dimensions. As you go further into smaller
dimensions, you will need very powerful microscopes to see the small bits.
There you will see that the chalk piece is made up of molecules. Molecules
can be spliced even smaller and can be split into some basic units called
atoms.
Atoms
are the basic building blocks of matter. There are many types of atoms in
the Universe. Molecules are made up of a combination of more than one atom.
For example, chalk is made up of calcium atom and carbon atom; the molecule
of chalk is calcium carbonate.
Pure
substances like gold are solely made up of gold atoms. Another word
describing pure substances is Element.
There are more than 120 elements, of which only about 92
elements are found naturally on the earth.
To name a few common ones : Hydrogen, Helium, Sodium,
Aluminum, Chlorine, Iron, Copper, Silver, and Gold. Each of these elements
is made of their respective atoms. It has to be borne in mind that atoms of
different elements have different and unique characteristics. |
|
| All atoms are made up of protons, neutrons and electrons. It is the way
these subatomic particles are arranged that gives each atom its unique
characteristics.
|
|
Atoms of some elements like to
combine with atoms of other elements. Such a combination is called a Compound. The combination is in a definite
proportion. The example of chalk above was that of a compound.
Common salt is made up of sodium atoms and chlorine atoms, which
combine into sodium chloride molecule. Water is a compound made up of
hydrogen and oxygen atoms. If
you take two electrodes and insert in a beaker of water, you will be able to
collect oxygen and hydrogen gases at the ends of the two electrodes.
Properties of water are entirely different from that of oxygen and
hydrogen. Water is a liquid whereas the elements from which it is made are
gaseous.
|
Electrolysis of water
|
In
a compound, each of the constituent atoms loose their individuality and
start displaying a totally new property of the compound formed. The smallest
basic unit of a compound that can maintain and display its properties is
called a molecule. For a compound to get formed, a chemical reaction between the
constituent atoms has to take place.
Although there are less than
100 elements or pure substances in nature, there are millions and millions of
compounds formed by various permutation and combination of elements.
Compounds generally decompose on heating and may either separate into the
constituent elements or change into another compound.
Substances can also be made up of
combinations of compounds, and are called Mixtures.
In a mixture, the individual constituents retain their original properties.
For example, if you take brine (salt solution), it is a mixture of salt
(sodium chloride) and water. If
you boil brine, you will be able to separate and get back pure water and
pure salt. If you take lemon sherbet, you will be able to separate lemon
juice, water, sugar and salt from it.
|
|
|
|
|
Recovery of salt from brine solution by heating
|
In a mixture, the constituents do not
chemically combine to give a totally new substance, the type that happens
during the formation of a compound. The
example for brine is that of a homogenous
mixture, where one compound is completely soluble in the other compound;
the mixture displays the same property throughout its bulk. There are cases when
the mixture consists of compounds that are not soluble with each other. In
this case the mixture is called a heterogeneous
mixture. An example of a heterogeneous mixture would be liquid mixes of
oil and water, mud and water, etc. Mixtures can be separated into their
constituent parts by various processes such as evaporation
(see the above figure),
distillation, filtration, etc.
To
sum up our categorization of substances pictorially, see the following
diagram:
|
|
