Class 9 - Chemistry - Chapter 1

Introduction to Chemistry

Chemistry:

The branch of science which deals with the composition and properties of matter, changes in matter and the laws or principles which govern these changes is called Chemistry.

Branches of Chemistry:

Physical Chemistry

The branch of chemistry which deals with the physical properties and physical behavior of material things is called physical chemistry.

Inorganic Chemistry

The study of all elements and their compounds except carbon is called inorganic chemistry.

Organic Chemistry

The branch of chemistry in which we study the compounds of carbon is called organic chemistry.

Analytical Chemistry

The branch of chemistry which discusses the analytical methods for getting information about chemical compounds and chemical processes is called analytical chemistry.

Biochemistry

The study of chemical compounds present in living things is called biochemistry.

Industrial Chemistry

The application of chemical knowledge in technology and industry and the preparation of industrial products are called industrial chemistry.

Steps Involved in Getting Information in the Scientific Method:

Science is not only an integrated knowledge of physical and biological phenomena but also the methodology through which this knowledge is gathered. The process of scientific discoveries is a cyclic process.

In science the facts are gathered through observations and experiments and then theories or law are deduced. The scientific method include following four steps:

1. Observation

2. Inference

3. Prediction

4. Experiment

Observation

The observations are made by the five senses of man. Men made equipments are also used for making observations. For example microscope is used for observing minute objects. Thermometer is used to measure temperature. Sensitive balance is used to determine the mass of a very light object. The capacity of man made instruments is also limited. But it can be improved by improving technology. Thus better and more reliable information are given to the scientists who produce better result. Information acquired through careful observations are called facts. These facts are foundation of scientific knowledge.

Inference

The facts gathered through observations are carefully arranged and properly classified. Correlating the knowledge thus acquired with previous knowledge, we try to think of a tentative solution to explain the observed phenomenon. The tentative solution is called hypothesis. The validity of this hypothesis is tested through the results obtained from experiments. The results are discussed by the scientists and the hypothesis is accepted or rejected. The accepted hypothesis then takes the form of theory. A theory when repeatedly gives the same results after experimentation and gives correct explanation of the scientific facts becomes a law or principle.

A theory remains valid until contrary informations are given on the basis of experimentation. Thus a hypothesis requires experimental support. But Avogadro's hypothesis has been accepted as law without any experimental support.

Prediction

Facts, theories and laws which are deduced from observation can help in deducing more facts and phenomenon. This process is called prediction.

Experiment

An experiment is an integrated activity, which is performed under suitable conditions with specially designed instruments to get the required information. Such information is used to test the validity of the hypothesis. If a hypothesis is proved correct. It increases the reliability of known facts. If it is proved wrong, it still can give information which can be used to deduce other results.

Chemistry and Society:

Chemistry has played important role for well being of mankind in the form of food, clothing, shelter, medical treatment and chemical fertilizers, crops protected by insecticides, refined food and production of artificial fiber. Productions of cement, iron bricks, glass, paint etc are all due to chemistry.

The hazards of chemistry are so vast that no aspect of human life has remained unaffected. The smoke coming from chimneys of chemical industries and from vehicles pollutes the air. It is very dangerous to breath in that air. Similarly waste water from industry, pollute canals, rivers and has bad effect on land. Excessive chemical spray on plants also has bad effect.