Before we go to the subject matter there is need to understand Chemistry as:

1. (Chemistry) the branch of physical science concerned with the composition,
properties, and reactions of substances.
2. (Chemistry) the composition, properties, and reactions of a particular substance
3. The nature and effects of any complex phenomenon: the chemistry of humour.
4. Informal, a reaction, taken to be instinctual, between two persons.


Pure Chemistry is simply the study of the facts and theories of chemistry in their purely scientific relations, without necessary reference to their practical applications or mere utility.

For Example; studying The modern theory of matter dates from the work of John Dalton at the beginning of the 19th century.

The atom is considered the basic unit of any element, and atoms may combine chemically to form molecules, the molecule being the smallest unit of any substance that possesses the properties of that substance.

An element in modern theory is any substance all of whose atoms are the same (i.e., have the same atomic number),

while a compound is composed of different types of elements together in molecules.

Physical and Chemical Changes

The difference between a mixture and a compound helps to illustrate the difference between a physical change and a chemical change.

Different atoms may also be present together in a mixture, but in a mixture, they are not bound together chemically as they are in a compound.

In physical change, it involves a change of state of matter (e.g., from solid to liquid), the substance as a whole changes, but its underlying structure remains the same; water is still composed of molecules containing two hydrogen atoms and one oxygen atom whether it is in the form of ice, liquid water, or steam.

In a chemical change, however, the substance participates in a chemical reaction, with a consequent reordering of its atoms.

As a result, it becomes a different substance with a different set of properties.

Many of the physical properties and much of the behavior of matter can be understood without detailed assumptions about the structure of atoms and molecules.

For example, the kinetic-molecular theory of gases provides a good explanation of the nature of temperature and the basis of the various gas laws and also gives insight into the different states of matter.

Substances in different states vary in the strength of the forces between their molecules, with intermolecular forces being strongest in solids and weakest in gases.

The force holding like molecules together is called cohesion, while that between unlike molecules is called adhesion.

Among the phenomena resulting from intermolecular forces are surface tension and capillarity.

An even larger number of aspects of matter can be understood when the nature and structure of the atom are taken into account.

The quantum theory has provided the key to understanding the atom, and most basic problems relating to the atom have been solved.

The Relationship of Matter and Energy


The atomic theory of matter does not answer the question of the basic nature of matter. It is now known that matter and energy are intimately related.

According to the law of mass-energy equivalence, developed by Albert Einstein as part of his theory of relativity, a quantity of matter of mass m possesses an intrinsic rest mass energy E given by E= mc 2, where c is the speed of light. This equivalence is dramatically demonstrated in the phenomena of nuclear fission and fusion in which a small amount of matter is converted to a rather large amount of energy.

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