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Chemistry is the science of molecules and their transformation. It is the science not so much of the one hundred elements but of th...

SOME BASIC CONCEPTS OF CHEMISTRY






Chemistry is the science of molecules and their transformation. It is the science not so much of the one hundred elements but of the infinite variety of molecules that may be built from them.   -- Roald Hoffmann
Chemistry is the branch of science that studies the composition, properties, and interactions of matters. 

1. IMPORTANCE OF CHEMISTRY
Chemistry plays a central role in science and often connected with other branches of sciences of biology, physics, geology, etc. 

Chemistry also plays a role in daily life. 

Chemistry is used in chemical industries for manufacturing acids, salts, dyes, drugs, soaps, polymers, mettle, alloys, and other inorganic and organic chemicals. 




2. NATURE OF MATTER

Anything that has mass and occupies space is called matter. Everything around us like pen, book, table, etc are examples of matter.

Matter can exist in three physical states- solid, liquid, and gas. In solid, the particles are very close to each other and there is no movement in particles, and particles are ordered. In liquid, the particles are close to each other but they can move. However, in the gases, particles are very far apart as compared to other states of matters.
Due to the physical states of matter, the following things can be observed,
(i) Solids have definite volume and definite shape.
(ii) Liquids have a definite volume but not the definite shape. They take the shape of the container in which they are placed.
(iii) Gases have neither a definite volume nor a definite shape. They completely occupy the container in which they are placed.

These three states of matter are interconvertible by changing the conditions of temperature and pressure.

Solid (on heating) --> liquid (on heating) --> Gas
Gas (on cooling) --> Liquid (on cooling) --> Solid

On heating, a solid usually changes to a liquid and the liquid on further heating changes to gases. 

The matter can be classified as mixtures or pure substances.
 These can be further sub-divided as shown in Fig. 1.2.


Matter: Anything that has mass and occupies space is called matter. for example, everything around us like pen, book, table, etc are matters.
Mixture: When two or more substances are present in any ratio then it is called a mixture. For example, a sugar solution in water, air, milk, etc are examples of the mixture.
The mixture can be either homogeneous or heterogeneous. When the components of mixtures are completely mixed and uniform throughout the solution, it is the type of homogeneous mixture and the components of homogeneous mixtures cannot be separated. For example, the solution of sugar in water, air, etc. On the other hand, when the components of any mixtures can easily be seen and it is not uniform throughout the solution, it is the type of heterogeneous mixture. For example, the mixtures of salt and sugar, grains, and pulses along with some stone pieces, are heterogeneous mixtures.

Pure substance:  A pure substance has a fixed composition of components whereas mixture may contain the components in any ratio. Gold, silver, water are examples of pure substance. Also, the components of a pure substance cannot be easily separated by simple physical methods. Further, a pure substance can be classified as elements and compounds. An element consists of a single type of particle. These particles may be atoms or molecules(two or more atoms combine to give molecules). Hydrogen, silver, copper, etc are some examples of elements. 
When two or more atoms of different elements combine, it forms a compoundExamples of some compounds are carbon dioxide, water, sugar, etc. The molecules of water and carbon dioxide are represented in Fig 1.4

3. PROPERTIES OF MATTER AND THEIR MEASUREMENT
Every substance has a unique characteristic or properties. These properties can be classified into two categories – physical properties and chemical properties. 

Physical properties are those properties that can be measured or observed without changing the identity or the composition of the substance. Some examples of physical properties are colour, odour, melting point, boiling point, density, etc. 

The measurement or observation of chemical properties requires a chemical change to occur. Examples of chemical properties are characteristic reactions of different substances; these include acidity or basicity, compatibility, etc.

3.1 Mass and Weight 
Mass of a substance is the amount of matter present in it while weight is the force exerted by gravity on an object. The mass of a substance is constant whereas its weight may vary from one place to another due to change in gravity. You should be careful in using these terms.


5. LAWS OF CHEMICAL COMBINATIONS
5.1 Law of Conservation of Mass
5.2 Law of Definite Proportions
5.3 Law of Multiple Proportions
5.4 Gay Lussac’s Law of Gaseous Volumes
5.5 Avogadro Law

6. DALTON’S ATOMIC THEORY
7. ATOMIC AND MOLECULAR MASSES
7.1 Atomic Mass
7.2 Average Atomic Mass
7.3 Molecular Mass
7.4 Formula Mass

8. MOLE CONCEPT AND MOLAR MASSES
9. PERCENTAGE COMPOSITION
9.1 Empirical Formula for Molecular Formula

10. STOICHIOMETRY AND STOICHIOMETRIC CALCULATIONS





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