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Some basic concepts of chemistry





Importance Of chemistry

Chemistry is the branch of science that deals with the composition, structure and properties of matter. Chemistry is called the science of atoms and molecule
This can be categorized into Organic and Inorganic chemistry, Physical chemistry, Bio-chemistry
Chemistry plays important role in daily life of humans

Nature of Matter

Anything which occupies space and has mass is called matter. Air and water, sugar and sand, hydrogen and oxygen etc.
  • Ancient Indian philosophers said that all the matter, living or non-living was made up of five basic elements (panch tatva): air, earth, fire, sky and water.
  • Modern day scientists classify matter in two ways: based on its physical properties and based on its chemical properties.
  • Based on physical properties, matter is classified as solids, liquids and gases.
  • Based on chemical properties, matter is classified as elements, compounds and mixtures.

Physical States of matter:

Based on physical state, all the matter can be classified into three groups: Solids, Liquids and Gases.

Properties of Solids, Liquids and Gases:
S.No.
Solids
Liquids
Gases
1.
Solids have a fixed shape and fixed volume
Liquids have fixed volume but they have no fixed shape
Gases have neither a fixed shape nor a fixed volume
2.
Solids cannot be compressed much
Liquids cannot be compressed much
Gases can be compressed easily
3.
Solids have high densities
Liquids have moderate to high densities
Gases have very low densities
4.
Solids do not fill their container completely
Liquids do not fill their container completely
Gases fill their container completely
5.
Solids do not flow
Liquids generally flow easily
Gases flow easily
6.
For example: Ice, coal, wood, stone, iron, etc.
Water, milk, fruit juice, ink, petrol, etc.
Air, oxygen, hydrogen, nitrogen, steam, etc.











Chemical Classification Of matter

Based upon the composition, matter can be divided into two main types:

1. Pure substances:A pure substance may be defined as a single substance (or matter) which cannot be separated by simple physical methods.
Pure substances can be further classified as (i) Elements (ii) Compounds
(i) Elements:An element consists of only one type of particles. These particles may be atoms or molecules.
For example, sodium, copper, silver, hydrogen, oxygen etc. are some examples of elements. They all contain atoms of one type. However, atoms of different elements are different in nature. Some elements such as sodium or copper contain single atoms held together as their constituent particles whereas in some others two or more atoms combine to give molecules of the element. Thus, hydrogen, nitrogen and oxygen gases consist of molecules in which two atoms combine to give the respective molecules of the element.
There are 114 elements known to us, out of which 92 are naturally occurring while the rest have been prepared artificially.
Elements are further classified into metals, non-metals and metalloid's
Some basic concepts of chemistry-Elements classification

(ii) Compounds:Compound is a pure substance containing two or more elements combined in a fixed proportion by weight and can be decomposed into these elements by suitable chemical methods. It is important to note that the properties of a compound are altogether different from the constituting elements.
The compounds have been classified into two types. These are:
(a) Inorganic Compounds:
Inorganic compounds are those, which are obtained from non-living sources such as minerals. For example, common salt, marble and limestone

(b) Organic Compounds:
Organic compounds are those, which occur in living sources such as plants and animals. They all contain carbon. Common organic compounds are oils, wax, fats etc.
Some basic concepts of chemistry - Compound classifications

2. Mixtures:The combination of two or more elements or compounds which are not chemically combined and may also be present in any proportion, is called mixture. A few examples of mixtures are: milk, sea water, petrol, lime water, paint glass, cement, wood etc.
Types of mixtures:
Mixtures are of two types:
(i) Homogeneous mixtures:A mixture is said to be homogeneous if it has a uniform composition throughout and there are no visible boundaries of separation between the constituents.
For example: A mixture of sugar solution in water has the same sugar water composition throughout and all portions have the same sweetness.
(ii) Heterogeneous mixtures:A mixture is said to be heterogeneous if it does not have uniform composition throughout and has visible boundaries of separation between the various constituents. The different constituents of a heterogeneous mixture can be seen even with naked eye.
For example: When iron filings and sulphur powder are mixed together, the mixture formed is heterogeneous. It has greyish-yellow appearance and the two constituents, iron and sulphur, can be easily identified with naked eye.
Differences between Compounds and Mixtures

Compounds
Mixtures
1. In a compound, two or more elements are combined chemically.
2. In a compound, the elements are present in the fixed ratio by mass. This ratio cannot change.
3. They are always homogeneous i.e., they have the same composition throughout.
4. The constituents of compound cannot be separated by physical methods
5. The constituents of compound lose their identities i.e., compound does not show the characteristics of the constituting elements.

1) In a mixture, or more elements or compounds are simply mixed and not combined chemically.
2. In a mixture the constituents are not present in fixed ratio. It can vary
3. Mixtures may be either homogeneous or heterogeneous in nature.
4. Constituents of mixtures can be separated by physical methods.
5, The constituents in mixture do not lose their identities i.e., a mixture shows the
characteristics of all the constituents.


Some basic concepts of chemistry|Class 11 Chemistry Chapter 1

Properties of Matter


We have physical and chemical properties of Matter
Physical Properties
They are the properties which can be measured or observed without changing the identity or the composition of the substance. E.g. colour, odour, melting point, boiling point, density etc.
Chemical Properties
are characteristic reactions of different substances; these include acidity or basicity, combustibility


Fill in the blanks

(1) Pure substances can be divided into _______ and compounds.
(2)There are _____ elements known to us, out of which 92 are naturally occurring while the rest have been prepared artificially.
(3) _____ is a pure substance having two or more elements combined in a fixed proportion by weight and can be decomposed into these elements by suitable chemical methods.
(4) __________________ compounds are those, which are obtained from non-living sources such as minerals.
(5) The combination of two or more elements or compounds which are not chemically combined and may also be present in any proportion, is called __________________.
(6) A homogeneous mixture has a uniform __________________ throughout and there are no visible boundaries of separation between the constituents.
(7)A ________ mixture does not have uniform composition throughout and has visible boundaries of separation between the various constituents.
(8)colour, odour, melting point, boiling point, density are _________________________________ Properties.
(9) __________________ compounds are those, which occur in living sources such as plants and animals and They all contain __________________.
(10)acidity or basicity, combustibility are _________________________________ Properties.



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