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
1
,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
102 hecto h
103 kilo k
106 mega M
109 giga G
1012 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 m3 or cm3 or
dm3.A common unit, litre (L) is not an SI unit, is used for measurement of volume of
liquids. 1 L = 1000 mL, 1000 cm3 = 1 dm3
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/m3 or kg m–3This 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.
2
, 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 x102 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 1023) 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
3
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
1
,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
102 hecto h
103 kilo k
106 mega M
109 giga G
1012 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 m3 or cm3 or
dm3.A common unit, litre (L) is not an SI unit, is used for measurement of volume of
liquids. 1 L = 1000 mL, 1000 cm3 = 1 dm3
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/m3 or kg m–3This 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.
2
, 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 x102 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 1023) 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
3
