Concept of Chemistry[class=11][part=1]

What is Chemistry?

• Chemistry is the science of atoms, molecules and their transformations.
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• It can also be defined as that branch of science that deals with the study of the composition, properties and interaction of matter.
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• Knowledge of chemistry helps us to know:-

1. The properties of different substances like diamond, coal, plastics etc.
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3. In preparation of soaps like liquid or powder.
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5. The fabrics, plastic toys, paper, pencil, eraser, sugar cubes, petrol or diesel etc.
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7. In the manufacture of different types of fertilizers, pesticides and medicines.
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9. Answers to questions regarding how many atoms or molecules are there in a given mass of matter.

Chemistry helps us to answer the following questions:-

• To count the number of atoms and molecules in a given mass of matter?
• How to see the atoms and molecules?

Advantages of studying chemistry

1. With a better understanding of chemical principles it has now become possible to design and synthesise new materials having specific magnetic, electric and optical properties.

Problems which can be tackled with the study of chemistry:-

1.  production of chemicals and synthesis of new exotic materials are some of the intellectual challenges for the future generation of chemists.
2. Understanding of bio-chemical processes, use of enzymes for large-scale production of chemicals.
3. Matter
   • Anything that has mass and occupies space is defined as matter.
     • For example:-soap, notebook, pencil, apple, battery etc.
   Physical States of matter
   • Matter can exist in 3 physical states namely solid, liquid and gas.
   
   Solids
   • In case of solids, the constituent particles are held very close to each other in an orderly fashion and there is not much freedom of movement.
   • Solids have definite shape and definite volume.
     • For example: - Table,Book etc
   Liquids
   • In liquids, the particles are close to each other but they can move around.
   • Liquids have definite volume but not definite shape. They take the shape of the container in which they are placed.
     • For example:milk,Water etc.
   Gases
   • In gases, the particles are far apart as compared to those present in solid or liquid states and their movement is easy and fast.
   • If container in which they are placed.
     • For example: - Air,gases etc..
   
   •  Important facts ----
   • All the 3 states of matter are inconvertible among each other.
   • Consider solid  if we melt it , it changes  into  liquid  and  if it is further  heated  it  becomes 
   • When the gas is condensed they change to liquid. And when the liquid is freezed it becomes solid.
   • By sublimation  solid  changes  into  gas  and  gas  by deposition  it  becomes 
   
   Matter at macroscopic level
   
4. Pure Substances
   • Pure substances have fixed composition.
     • For example: -  gold, water, glucose ,Copper, silver, etc.
       • Composition of carbon, hydrogen and oxygen in sugar will be always C12H22O11.They will be always in fixed ratio.
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     • Also, the constituents of pure substances cannot be separated by simple physical methods
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     • Pure substances are further classified into-
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     • [1]- Elements 
     • [2]- Compounds.
     • An element consists of only one type of particles. These particles may be atoms or molecules.
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     • For example: -  copper (Cu), silver (Ag), hydrogen (H), oxygen (O) atoms etc. They contain only one type of atoms.
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     • When two or more atoms of different elements combine, the molecule of a compound is obtained.
     • For example: - Water (H20), Ammonia (NH3), Sugar, carbon dioxide (CO2).
   Representation of atoms and molecules
   
   • The properties of a compound are different from those of its constituent elements.
   
   
   For example: - Hydrogen (H2) and Oxygen (O2) are gases whereas the compound formed by their combination i.e., water (H20) is a liquid.
   
   • NOTES--Hydrogen burns with a pop sound and oxygen is a supporter of combustion, but water is used as a fire extinguisher.
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   • Constituents of a compound cannot be separated into simpler substances by physical methods. They can be separated by chemical methods.
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   • A mixture contains two or more substances present in it (in any ratio) which are called its components.
   • For example:-Air, sugar solution, mixture of pulse .
   
   • A mixture can be homogeneous or heterogeneous.
   • In homogeneous mixture, the components completely mix with each other and its composition is uniform throughout.
   • For example: - Air, Sugar solution.
   • In heterogeneous mixtures, the composition is not uniform throughout and sometimes the different components can be observed.
   • For example: - Mixture of dal mot and bhujia, badam etc.
     • NOTES  ----The components of a mixture can be separated by using physical methods such as simple hand picking, filtration, crystallisation, distillation etc.