Chemistry is the science of atoms and molecules.
Chemistry is the branch of science in which we study about the composition, properties and interaction of matter.
Importance of Chemistry: Today we can’t even imagine our life without Chemistry. In day to day life, We are habitual of the products made by the help of Chemistry. Some of the important applications of Chemistry are as follows:
I. In Domestic Goods : Several products like soap, surf, cleaning materials, shaving creams, shampoos etc are produced by the methods and techniques of Chemistry. Insect killers, mosquito coils, cells are also very important products for domestic use.
II. In Medicines: We all know the importance of medicines in our life. Medicines are just the boons of Chemistry. For example: aziodothymedicine for AIDS, paracetamol for fever etc.
III. In Agriculture: The importance of fertilisers is well known. Without the help of Chemistry it can’t be possible to make different types of fertilisers like urea, sodium nitrate etc. To save our crop we use different kinds of insecticides or pesticides which can’t be produced without the help of chemistry.
IV. In Lifestyle: We can’t imagine our life without Clothes, shoes, different beauty products etc today. Building materials like cement, steel are the boons of Chemistry. In short we can say that Chemistry has just changed our lifestyle.
V. In transportation: About all the means of transportation require petrol, diesel, CNG or coal for fuel which are prepared by the help of principles of Chemistry.
VI. In war: Explosives like TNT, nitroglycerin and dynamite are integrated part of wars today. These have been developed by the help of Chemistry.
Branches of Chemistry: The field of Chemistry has become very wide and broad due to which it has been divided into several branches.
I. Physical Chemistry : It deals with the applications of different principles of Chemistry.
II. Inorganic Chemistry : We study about the elements other than carbon & their compounds.
Matter: Anything which occupies some space and has some mass is called matter. Ex : book, pen, board, copy, bottle etc
Classification of matter: Matters are classified on two bases :
1. Physical classification: on this basis matters are classified into three categories:
I. Solid: Substances having definite shape and volume are called solids. Ex: books, pen, copy
Properties of matter: Each matter has some properties which are classified as follows:
Physical properties: Properties which can be observed without changing the identity are called physical properties. Ex: mass, volume, density, melting point, boiling point etc.
Chemical properties: Properties which can’t be observed without changing the identity are called physical properties. Ex: combustibility etc
Measurement of properties: To know about any matter we need to measure its properties. To measure any property of matters, units are required. Generally, different countries have different systems of units due to which understanding problems are generated. To solve this problem a system was developed which is accepted at international level and which is named as SI system. The full name of it is: The international system of units.
SI System: In this system, there are seven base or fundamental units explained below:
Definition of base units:
1. Kilogram : The mass of platinum iridium(Pt-Ir) cylinder that is kept in vacuum in a jar at International Bureau of Weights and Measures in France is called 1 kilogram.
2.Metre : The length of the path travelled by light in vacuum during a time interval of 1/299, 792, 458 part of a second.
3. Second: The second is the duration of 9 192, 631, 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the levels of ground state of Cs-133 atom.
Measurement of properties: To know about a matter, we have to know about its properties. Some of the properties are as follows:
1.Mass & Weight: Mass of a substance is the amount of matter present in it. It is constant in any condition.
Weight is the force applied on a substance due to gravity. It varies from place to place because of the change in the gravitational force.
2. Volume : Three lengths are involved in the volume of anything. So, SI unit for volume is m3.
3. Density: The mass per unit volume of a substance is called its density. It is generally denoted by d.
Density = mass / volume
Its unit is kg/m3
Key Point: Some important physical quantities and their units are as follows:
⧫ Velocity : m/s ⧫ Acceleration : m/s2 ⧫ Force : kg m/s2
Significant figures: Meaningful digits in a number which are known with certainty are called significant figures.
Ex : In 0.0056 has two significant figures 5 & 6.
Rules for determining significant figures:
1. All non-zero digits are significant in a number.
2. Zeros before the 1st non-zero digit are not significant.
3. Zeros between two non-zero digits are significant.
4. Zeros at the end or right of a non-zero number after the decimal point are significant. Ex : 0.200 has three significant figures