CH 1 Some basic concepts of chemistry Class 11 Notes | EduRev

Class 11 : CH 1 Some basic concepts of chemistry Class 11 Notes | EduRev

 Page 1


1 
 
UNIT 1 
SOME BASIC CONCEPTS OF CHEMISTRY 
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 
Branches of Chemistry 
 Organic Chemistry -This branch deals with study of carbon compounds 
especially hydrocarbons and their derivatives. 
 Inorganic Chemistry-This branch deals with the study of compounds of all 
other elements except carbon. It largely concerns itself with the study of 
minerals found in the Earth's crust. 
 Physical Chemistry-The explanation of fundamental principles governing 
various chemical phenomena is the main concern of this branch. It is basically 
concerned with laws and theories of the different branches of chemistry. 
 Industrial Chemistry-The chemistry involved in industrial processes is studied 
under this branch. 
 Analytical Chemistry-This branch deals with the qualitative and quantitative 
analysis of various substances. 
 Biochemistry-This branch deals with the chemical changes going on in the 
bodies of living organisms; plants and animals. 
 Nuclear Chemistry-Nuclear reactions, such as nuclear fission, nuclear fusion, 
transmutation processes etc. are studied under this branch. 
PROPERTIES OF MATTER AND THEIR MEASUREMENT--Every substance 
has unique or characteristic properties. These properties can be classified into two 
categories – physical properties and chemical properties. 
Physical properties are those 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. 
The measurement or observation of chemical properties requires a chemical change 
to occur. e.g. Burning of Mg-ribbon in air 
Chemical properties are characteristic reactions of different substances; these 
include acidity or basicity, combustibility etc.Many properties of matter such as 
length, area, volume, etc., are quantitative in nature. 
Metric System was based on the decimal system.  
The International System of Units (SI) 
The International System of Units (in French Le Systeme International d’Unites– 
abbreviated as SI) was established by the 11th General Conference on Weights and 
Measures (CGPM from ConferenceGenerale des Poids at Measures). The SI system 
has seven base units  
 
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CBSE sample papers, Question papers, Notes for Class 6 to 12 
Please Visit www.ncerthelp.com For Video lectures of all subjects Class 9 to 12 
Page 2


1 
 
UNIT 1 
SOME BASIC CONCEPTS OF CHEMISTRY 
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 
Branches of Chemistry 
 Organic Chemistry -This branch deals with study of carbon compounds 
especially hydrocarbons and their derivatives. 
 Inorganic Chemistry-This branch deals with the study of compounds of all 
other elements except carbon. It largely concerns itself with the study of 
minerals found in the Earth's crust. 
 Physical Chemistry-The explanation of fundamental principles governing 
various chemical phenomena is the main concern of this branch. It is basically 
concerned with laws and theories of the different branches of chemistry. 
 Industrial Chemistry-The chemistry involved in industrial processes is studied 
under this branch. 
 Analytical Chemistry-This branch deals with the qualitative and quantitative 
analysis of various substances. 
 Biochemistry-This branch deals with the chemical changes going on in the 
bodies of living organisms; plants and animals. 
 Nuclear Chemistry-Nuclear reactions, such as nuclear fission, nuclear fusion, 
transmutation processes etc. are studied under this branch. 
PROPERTIES OF MATTER AND THEIR MEASUREMENT--Every substance 
has unique or characteristic properties. These properties can be classified into two 
categories – physical properties and chemical properties. 
Physical properties are those 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. 
The measurement or observation of chemical properties requires a chemical change 
to occur. e.g. Burning of Mg-ribbon in air 
Chemical properties are characteristic reactions of different substances; these 
include acidity or basicity, combustibility etc.Many properties of matter such as 
length, area, volume, etc., are quantitative in nature. 
Metric System was based on the decimal system.  
The International System of Units (SI) 
The International System of Units (in French Le Systeme International d’Unites– 
abbreviated as SI) was established by the 11th General Conference on Weights and 
Measures (CGPM from ConferenceGenerale des Poids at Measures). The SI system 
has seven base units  
 
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CBSE sample papers, Question papers, Notes for Class 6 to 12 
Please Visit www.ncerthelp.com For Video lectures of all subjects Class 9 to 12 
2 
 
 
 
Prefixes in SI system 
  
Multiple Prefix Symbol 
10
-12
 pico p 
10
-9
 nano n 
10
-6
 micro µ 
10
-3
 milli m 
10
-2
 centi c 
10
-1
 deci d 
10 deca da 
10
2
 hecto h 
10
3
 kilo k 
10
6
 mega M 
10
9
 giga G 
10
12
 tera T 
 
 
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. The mass of a substance can be determined very accurately by using an 
analytical balance 
Volume-- Volume has the units of (length)
3
. So volume has units of m
3
 or cm
3
 or 
dm
3
.A common unit, litre (L) is not an SI unit, is used for measurement of volume of 
liquids. 1 L = 1000 mL, 1000 cm
3
 = 1 dm
3
 
Density: Density of a substance is its amount of mass per unit volume.SI unit of 
density = SI unit of mass/SI unit of volume = kg/m
3
 or kg m
–3
This unit is quite large 
and a chemist often expresses density in g cm
–3
. 
Temperature--There are three common scales to measure temperature — °C (degree 
celsius), °F (degree Fahrenheit) and K (kelvin). Here, K is the SI unit. 
 
K = °C + 273.15 
Note—Temperature below 0 °C (i.e. negative values) are possible in Celsius scale 
but in Kelvin scale, negative temperature is not possible. 
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CBSE sample papers, Question papers, Notes for Class 6 to 12 
Please Visit www.ncerthelp.com For Video lectures of all subjects Class 9 to 12 
Page 3


1 
 
UNIT 1 
SOME BASIC CONCEPTS OF CHEMISTRY 
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 
Branches of Chemistry 
 Organic Chemistry -This branch deals with study of carbon compounds 
especially hydrocarbons and their derivatives. 
 Inorganic Chemistry-This branch deals with the study of compounds of all 
other elements except carbon. It largely concerns itself with the study of 
minerals found in the Earth's crust. 
 Physical Chemistry-The explanation of fundamental principles governing 
various chemical phenomena is the main concern of this branch. It is basically 
concerned with laws and theories of the different branches of chemistry. 
 Industrial Chemistry-The chemistry involved in industrial processes is studied 
under this branch. 
 Analytical Chemistry-This branch deals with the qualitative and quantitative 
analysis of various substances. 
 Biochemistry-This branch deals with the chemical changes going on in the 
bodies of living organisms; plants and animals. 
 Nuclear Chemistry-Nuclear reactions, such as nuclear fission, nuclear fusion, 
transmutation processes etc. are studied under this branch. 
PROPERTIES OF MATTER AND THEIR MEASUREMENT--Every substance 
has unique or characteristic properties. These properties can be classified into two 
categories – physical properties and chemical properties. 
Physical properties are those 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. 
The measurement or observation of chemical properties requires a chemical change 
to occur. e.g. Burning of Mg-ribbon in air 
Chemical properties are characteristic reactions of different substances; these 
include acidity or basicity, combustibility etc.Many properties of matter such as 
length, area, volume, etc., are quantitative in nature. 
Metric System was based on the decimal system.  
The International System of Units (SI) 
The International System of Units (in French Le Systeme International d’Unites– 
abbreviated as SI) was established by the 11th General Conference on Weights and 
Measures (CGPM from ConferenceGenerale des Poids at Measures). The SI system 
has seven base units  
 
Visit www.ncerthelp.com For All NCERT solutions, 
CBSE sample papers, Question papers, Notes for Class 6 to 12 
Please Visit www.ncerthelp.com For Video lectures of all subjects Class 9 to 12 
2 
 
 
 
Prefixes in SI system 
  
Multiple Prefix Symbol 
10
-12
 pico p 
10
-9
 nano n 
10
-6
 micro µ 
10
-3
 milli m 
10
-2
 centi c 
10
-1
 deci d 
10 deca da 
10
2
 hecto h 
10
3
 kilo k 
10
6
 mega M 
10
9
 giga G 
10
12
 tera T 
 
 
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. The mass of a substance can be determined very accurately by using an 
analytical balance 
Volume-- Volume has the units of (length)
3
. So volume has units of m
3
 or cm
3
 or 
dm
3
.A common unit, litre (L) is not an SI unit, is used for measurement of volume of 
liquids. 1 L = 1000 mL, 1000 cm
3
 = 1 dm
3
 
Density: Density of a substance is its amount of mass per unit volume.SI unit of 
density = SI unit of mass/SI unit of volume = kg/m
3
 or kg m
–3
This unit is quite large 
and a chemist often expresses density in g cm
–3
. 
Temperature--There are three common scales to measure temperature — °C (degree 
celsius), °F (degree Fahrenheit) and K (kelvin). Here, K is the SI unit. 
 
K = °C + 273.15 
Note—Temperature below 0 °C (i.e. negative values) are possible in Celsius scale 
but in Kelvin scale, negative temperature is not possible. 
Visit www.ncerthelp.com For All NCERT solutions, 
CBSE sample papers, Question papers, Notes for Class 6 to 12 
Please Visit www.ncerthelp.com For Video lectures of all subjects Class 9 to 12 
3 
 
Scientific Notation 
In which any number can be represented in the form N × 10
n
 (Where n is an exponent 
having positive or negative values and N can vary between 1 to 10). 
e.g. We can write 232.508 as 2.32508 x10
2
 in scientific notation. Similarly, 0.00016 
can be written as 1.6 x 10
–4
. 
Precision refers to the closeness of various measurements for the same quantity. 
Accuracy is the agreement of a particular value to the true value of the result 
Significant Figures 
The reliability of a measurement is indicated by the number of digits used to 
represent it. To express it more accuratelywe express it with digits that are known 
with certainty. These are called as Significant figures. They contain all thecertain 
digits plus one doubtful digit in a number. 
Rules for Determining the Number of Significant Figures 
 All non-zero digits are significant. For example, 6.9 has two significant 
figures, while 2.16 has three significantfigures. The decimal place does not 
determine the number of significant figures. 
 A zero becomes significant in case it comes in between non zero numbers. For 
example, 2.003 has four significantfigures, 4.02 has three significant figures. 
 Zeros at the beginning of a number are not significant. For example, 0.002 has 
one significant figure while 0.0045has two significant figures. 
 All zeros placed to the right of a number are significant. For example, 16.0 has 
three significant figures, while 16.00has four significant figures. Zeros at the 
end of a number without decimal point are ambiguous. 
 In exponential notations, the numerical portion represents the number of 
significant figures. For example, 0.00045 isexpressed as 4.5 x 10
-4
 in terms of 
scientific notations. The number of significant figures in this number is 2, 
while inAvogadro's number (6.023 x 10
23
) it is four. 
 The decimal point does not count towards the number of significant figures. 
For example, the number 345601 has sixsignificant figures but can be written 
in different ways, as 345.601 or 0.345601 or 3.45601 all having same number 
ofsignificant figures. 
 
 
Retention of Significant Figures - Rounding off Figures 
The rounding off procedure is applied to retain the required number of significant 
figures. 
1. If the digit coming after the desired number of significant figures happens to 
be more than 5, the precedingsignificant figure is increased by one, 4.317 is 
rounded off to 4.32. 
2. If the digit involved is less than 5, it is neglected and the preceding significant 
figure remains unchanged, 4.312 isrounded off to 4.31. 
3. If the digit happens to be 5, the last mentioned or preceding significant figure 
is increased by one only in case ithappens to be odd. In case of even figure, the 
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CBSE sample papers, Question papers, Notes for Class 6 to 12 
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Page 4


1 
 
UNIT 1 
SOME BASIC CONCEPTS OF CHEMISTRY 
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 
Branches of Chemistry 
 Organic Chemistry -This branch deals with study of carbon compounds 
especially hydrocarbons and their derivatives. 
 Inorganic Chemistry-This branch deals with the study of compounds of all 
other elements except carbon. It largely concerns itself with the study of 
minerals found in the Earth's crust. 
 Physical Chemistry-The explanation of fundamental principles governing 
various chemical phenomena is the main concern of this branch. It is basically 
concerned with laws and theories of the different branches of chemistry. 
 Industrial Chemistry-The chemistry involved in industrial processes is studied 
under this branch. 
 Analytical Chemistry-This branch deals with the qualitative and quantitative 
analysis of various substances. 
 Biochemistry-This branch deals with the chemical changes going on in the 
bodies of living organisms; plants and animals. 
 Nuclear Chemistry-Nuclear reactions, such as nuclear fission, nuclear fusion, 
transmutation processes etc. are studied under this branch. 
PROPERTIES OF MATTER AND THEIR MEASUREMENT--Every substance 
has unique or characteristic properties. These properties can be classified into two 
categories – physical properties and chemical properties. 
Physical properties are those 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. 
The measurement or observation of chemical properties requires a chemical change 
to occur. e.g. Burning of Mg-ribbon in air 
Chemical properties are characteristic reactions of different substances; these 
include acidity or basicity, combustibility etc.Many properties of matter such as 
length, area, volume, etc., are quantitative in nature. 
Metric System was based on the decimal system.  
The International System of Units (SI) 
The International System of Units (in French Le Systeme International d’Unites– 
abbreviated as SI) was established by the 11th General Conference on Weights and 
Measures (CGPM from ConferenceGenerale des Poids at Measures). The SI system 
has seven base units  
 
Visit www.ncerthelp.com For All NCERT solutions, 
CBSE sample papers, Question papers, Notes for Class 6 to 12 
Please Visit www.ncerthelp.com For Video lectures of all subjects Class 9 to 12 
2 
 
 
 
Prefixes in SI system 
  
Multiple Prefix Symbol 
10
-12
 pico p 
10
-9
 nano n 
10
-6
 micro µ 
10
-3
 milli m 
10
-2
 centi c 
10
-1
 deci d 
10 deca da 
10
2
 hecto h 
10
3
 kilo k 
10
6
 mega M 
10
9
 giga G 
10
12
 tera T 
 
 
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. The mass of a substance can be determined very accurately by using an 
analytical balance 
Volume-- Volume has the units of (length)
3
. So volume has units of m
3
 or cm
3
 or 
dm
3
.A common unit, litre (L) is not an SI unit, is used for measurement of volume of 
liquids. 1 L = 1000 mL, 1000 cm
3
 = 1 dm
3
 
Density: Density of a substance is its amount of mass per unit volume.SI unit of 
density = SI unit of mass/SI unit of volume = kg/m
3
 or kg m
–3
This unit is quite large 
and a chemist often expresses density in g cm
–3
. 
Temperature--There are three common scales to measure temperature — °C (degree 
celsius), °F (degree Fahrenheit) and K (kelvin). Here, K is the SI unit. 
 
K = °C + 273.15 
Note—Temperature below 0 °C (i.e. negative values) are possible in Celsius scale 
but in Kelvin scale, negative temperature is not possible. 
Visit www.ncerthelp.com For All NCERT solutions, 
CBSE sample papers, Question papers, Notes for Class 6 to 12 
Please Visit www.ncerthelp.com For Video lectures of all subjects Class 9 to 12 
3 
 
Scientific Notation 
In which any number can be represented in the form N × 10
n
 (Where n is an exponent 
having positive or negative values and N can vary between 1 to 10). 
e.g. We can write 232.508 as 2.32508 x10
2
 in scientific notation. Similarly, 0.00016 
can be written as 1.6 x 10
–4
. 
Precision refers to the closeness of various measurements for the same quantity. 
Accuracy is the agreement of a particular value to the true value of the result 
Significant Figures 
The reliability of a measurement is indicated by the number of digits used to 
represent it. To express it more accuratelywe express it with digits that are known 
with certainty. These are called as Significant figures. They contain all thecertain 
digits plus one doubtful digit in a number. 
Rules for Determining the Number of Significant Figures 
 All non-zero digits are significant. For example, 6.9 has two significant 
figures, while 2.16 has three significantfigures. The decimal place does not 
determine the number of significant figures. 
 A zero becomes significant in case it comes in between non zero numbers. For 
example, 2.003 has four significantfigures, 4.02 has three significant figures. 
 Zeros at the beginning of a number are not significant. For example, 0.002 has 
one significant figure while 0.0045has two significant figures. 
 All zeros placed to the right of a number are significant. For example, 16.0 has 
three significant figures, while 16.00has four significant figures. Zeros at the 
end of a number without decimal point are ambiguous. 
 In exponential notations, the numerical portion represents the number of 
significant figures. For example, 0.00045 isexpressed as 4.5 x 10
-4
 in terms of 
scientific notations. The number of significant figures in this number is 2, 
while inAvogadro's number (6.023 x 10
23
) it is four. 
 The decimal point does not count towards the number of significant figures. 
For example, the number 345601 has sixsignificant figures but can be written 
in different ways, as 345.601 or 0.345601 or 3.45601 all having same number 
ofsignificant figures. 
 
 
Retention of Significant Figures - Rounding off Figures 
The rounding off procedure is applied to retain the required number of significant 
figures. 
1. If the digit coming after the desired number of significant figures happens to 
be more than 5, the precedingsignificant figure is increased by one, 4.317 is 
rounded off to 4.32. 
2. If the digit involved is less than 5, it is neglected and the preceding significant 
figure remains unchanged, 4.312 isrounded off to 4.31. 
3. If the digit happens to be 5, the last mentioned or preceding significant figure 
is increased by one only in case ithappens to be odd. In case of even figure, the 
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CBSE sample papers, Question papers, Notes for Class 6 to 12 
Please Visit www.ncerthelp.com For Video lectures of all subjects Class 9 to 12 
4 
 
preceding digit remains unchanged. 8.375 is rounded off to 8.38 while8.365 is 
rounded off to 8.36. 
Dimensional Analysis During calculations generally there is a need to convert units 
from one system to other. This is called factor label method or unit factor method 
or dimensional analysis. 
For example- 5 feet and 2 inches (height of an Indian female) is to converted in SI 
unit  
1 inch = 2.54 x 10
-2
 m 
then, 5 feet and 2 inch = 62 inch 
 
Physical Classification of Matter 
Properties Solid Liquid Gas 
1. volume Definite Definite Indefinite 
2. Shape Definite Indefinite Indefinite 
3. Inter molecular 
force of attraction 
Very high Moderate Negligible / Very 
low 
4. arrangement of 
molecules 
Orderly arranged Free to move 
within the volume 
Free to move every 
where 
5. Inter molecular 
space 
Very small Slightly greater Very great 
7. Compressibility Not compressible Not compressible Highly 
compressible 
8. Expansion on 
heating 
Very little Very little Highly expand 
9. Rigidity Very rigid Not rigid knownas 
fluid 
Not rigid and 
known as fluid 
9. Fluidity Can’t flow Can flow Can flow 
10. Diffusion They can diffuse 
due to kinetic 
energy of 
liquid/gases 
Can diffuse And 
rate of diffusion is 
very fast 
Can diffuse And 
rate of diffusion is 
very fast 
Chemical Classification of matter--- 
 
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CBSE sample papers, Question papers, Notes for Class 6 to 12 
Please Visit www.ncerthelp.com For Video lectures of all subjects Class 9 to 12 
Page 5


1 
 
UNIT 1 
SOME BASIC CONCEPTS OF CHEMISTRY 
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 
Branches of Chemistry 
 Organic Chemistry -This branch deals with study of carbon compounds 
especially hydrocarbons and their derivatives. 
 Inorganic Chemistry-This branch deals with the study of compounds of all 
other elements except carbon. It largely concerns itself with the study of 
minerals found in the Earth's crust. 
 Physical Chemistry-The explanation of fundamental principles governing 
various chemical phenomena is the main concern of this branch. It is basically 
concerned with laws and theories of the different branches of chemistry. 
 Industrial Chemistry-The chemistry involved in industrial processes is studied 
under this branch. 
 Analytical Chemistry-This branch deals with the qualitative and quantitative 
analysis of various substances. 
 Biochemistry-This branch deals with the chemical changes going on in the 
bodies of living organisms; plants and animals. 
 Nuclear Chemistry-Nuclear reactions, such as nuclear fission, nuclear fusion, 
transmutation processes etc. are studied under this branch. 
PROPERTIES OF MATTER AND THEIR MEASUREMENT--Every substance 
has unique or characteristic properties. These properties can be classified into two 
categories – physical properties and chemical properties. 
Physical properties are those 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. 
The measurement or observation of chemical properties requires a chemical change 
to occur. e.g. Burning of Mg-ribbon in air 
Chemical properties are characteristic reactions of different substances; these 
include acidity or basicity, combustibility etc.Many properties of matter such as 
length, area, volume, etc., are quantitative in nature. 
Metric System was based on the decimal system.  
The International System of Units (SI) 
The International System of Units (in French Le Systeme International d’Unites– 
abbreviated as SI) was established by the 11th General Conference on Weights and 
Measures (CGPM from ConferenceGenerale des Poids at Measures). The SI system 
has seven base units  
 
Visit www.ncerthelp.com For All NCERT solutions, 
CBSE sample papers, Question papers, Notes for Class 6 to 12 
Please Visit www.ncerthelp.com For Video lectures of all subjects Class 9 to 12 
2 
 
 
 
Prefixes in SI system 
  
Multiple Prefix Symbol 
10
-12
 pico p 
10
-9
 nano n 
10
-6
 micro µ 
10
-3
 milli m 
10
-2
 centi c 
10
-1
 deci d 
10 deca da 
10
2
 hecto h 
10
3
 kilo k 
10
6
 mega M 
10
9
 giga G 
10
12
 tera T 
 
 
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. The mass of a substance can be determined very accurately by using an 
analytical balance 
Volume-- Volume has the units of (length)
3
. So volume has units of m
3
 or cm
3
 or 
dm
3
.A common unit, litre (L) is not an SI unit, is used for measurement of volume of 
liquids. 1 L = 1000 mL, 1000 cm
3
 = 1 dm
3
 
Density: Density of a substance is its amount of mass per unit volume.SI unit of 
density = SI unit of mass/SI unit of volume = kg/m
3
 or kg m
–3
This unit is quite large 
and a chemist often expresses density in g cm
–3
. 
Temperature--There are three common scales to measure temperature — °C (degree 
celsius), °F (degree Fahrenheit) and K (kelvin). Here, K is the SI unit. 
 
K = °C + 273.15 
Note—Temperature below 0 °C (i.e. negative values) are possible in Celsius scale 
but in Kelvin scale, negative temperature is not possible. 
Visit www.ncerthelp.com For All NCERT solutions, 
CBSE sample papers, Question papers, Notes for Class 6 to 12 
Please Visit www.ncerthelp.com For Video lectures of all subjects Class 9 to 12 
3 
 
Scientific Notation 
In which any number can be represented in the form N × 10
n
 (Where n is an exponent 
having positive or negative values and N can vary between 1 to 10). 
e.g. We can write 232.508 as 2.32508 x10
2
 in scientific notation. Similarly, 0.00016 
can be written as 1.6 x 10
–4
. 
Precision refers to the closeness of various measurements for the same quantity. 
Accuracy is the agreement of a particular value to the true value of the result 
Significant Figures 
The reliability of a measurement is indicated by the number of digits used to 
represent it. To express it more accuratelywe express it with digits that are known 
with certainty. These are called as Significant figures. They contain all thecertain 
digits plus one doubtful digit in a number. 
Rules for Determining the Number of Significant Figures 
 All non-zero digits are significant. For example, 6.9 has two significant 
figures, while 2.16 has three significantfigures. The decimal place does not 
determine the number of significant figures. 
 A zero becomes significant in case it comes in between non zero numbers. For 
example, 2.003 has four significantfigures, 4.02 has three significant figures. 
 Zeros at the beginning of a number are not significant. For example, 0.002 has 
one significant figure while 0.0045has two significant figures. 
 All zeros placed to the right of a number are significant. For example, 16.0 has 
three significant figures, while 16.00has four significant figures. Zeros at the 
end of a number without decimal point are ambiguous. 
 In exponential notations, the numerical portion represents the number of 
significant figures. For example, 0.00045 isexpressed as 4.5 x 10
-4
 in terms of 
scientific notations. The number of significant figures in this number is 2, 
while inAvogadro's number (6.023 x 10
23
) it is four. 
 The decimal point does not count towards the number of significant figures. 
For example, the number 345601 has sixsignificant figures but can be written 
in different ways, as 345.601 or 0.345601 or 3.45601 all having same number 
ofsignificant figures. 
 
 
Retention of Significant Figures - Rounding off Figures 
The rounding off procedure is applied to retain the required number of significant 
figures. 
1. If the digit coming after the desired number of significant figures happens to 
be more than 5, the precedingsignificant figure is increased by one, 4.317 is 
rounded off to 4.32. 
2. If the digit involved is less than 5, it is neglected and the preceding significant 
figure remains unchanged, 4.312 isrounded off to 4.31. 
3. If the digit happens to be 5, the last mentioned or preceding significant figure 
is increased by one only in case ithappens to be odd. In case of even figure, the 
Visit www.ncerthelp.com For All NCERT solutions, 
CBSE sample papers, Question papers, Notes for Class 6 to 12 
Please Visit www.ncerthelp.com For Video lectures of all subjects Class 9 to 12 
4 
 
preceding digit remains unchanged. 8.375 is rounded off to 8.38 while8.365 is 
rounded off to 8.36. 
Dimensional Analysis During calculations generally there is a need to convert units 
from one system to other. This is called factor label method or unit factor method 
or dimensional analysis. 
For example- 5 feet and 2 inches (height of an Indian female) is to converted in SI 
unit  
1 inch = 2.54 x 10
-2
 m 
then, 5 feet and 2 inch = 62 inch 
 
Physical Classification of Matter 
Properties Solid Liquid Gas 
1. volume Definite Definite Indefinite 
2. Shape Definite Indefinite Indefinite 
3. Inter molecular 
force of attraction 
Very high Moderate Negligible / Very 
low 
4. arrangement of 
molecules 
Orderly arranged Free to move 
within the volume 
Free to move every 
where 
5. Inter molecular 
space 
Very small Slightly greater Very great 
7. Compressibility Not compressible Not compressible Highly 
compressible 
8. Expansion on 
heating 
Very little Very little Highly expand 
9. Rigidity Very rigid Not rigid knownas 
fluid 
Not rigid and 
known as fluid 
9. Fluidity Can’t flow Can flow Can flow 
10. Diffusion They can diffuse 
due to kinetic 
energy of 
liquid/gases 
Can diffuse And 
rate of diffusion is 
very fast 
Can diffuse And 
rate of diffusion is 
very fast 
Chemical Classification of matter--- 
 
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5 
 
Elements 
An element is the simplest form of matter that cannot be split into simpler substances 
or built from simpler substances by any ordinary chemical or physical method. 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 metalloids. 
Compounds 
A compound is a pure substance made up of two or more elements combined in a 
definite proportion by mass, which could be split by suitable chemical methods. 
Characteristics of compound 
 Compounds always contain a definite proportion of the same elements by 
mass.  
 The properties of compounds are totally different from the elements from 
which they are formed.  
 Compounds are homogeneous. 
 Compounds are broadly classified into inorganic and organic compounds. 
Inorganic compounds are those, which areobtained from non-living sources 
such as minerals. For example, common salt, marble and limestone. 
Organiccompounds are those, which occur in living sources such as plants and 
animals. They all contain carbon. Commonorganic compounds are oils, wax, 
fats etc. 
Mixtures 
A mixture is a combination of two or more elements or compounds in any proportion 
so that the components do not lose their identity. Air is an example of a mixture  
Mixtures are of two types, homogeneous and heterogeneous. 
Homogeneous mixtures have the same composition throughout the sample. The 
components of such mixtures cannot be seen under a powerful microscope. They are 
also called solutions. Examples of homogeneous mixtures are air, seawater, gasoline, 
brass etc. 
Heterogeneous mixtures consist of two or more parts (phases), which have different 
compositions. These mixtures have visible boundaries of separation between the 
different constituents and can be seen with the naked eye e.g., sand and salt, chalk 
powder in water etc. 
LAWS OF CHEMICAL COMBINATIONS 
Law of Conservation of Mass (Given by Antoine Lavoisier in 1789). 
It states that matter (mass) can neither be created nor destroyed. 
Law of Definite Proportions or Law of Constant Composition: 
This law was proposed by Louis Proust in 1799, which states that: 
'A chemical compound always consists of the same elements combined together in 
the same ratio, irrespective of the method of preparation or the source from where it 
is taken'. 
Law of Multiple Proportions Proposed by Dalton in 1803, this law states that: 
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