UNIT I: Some Basic Concepts of Chemistry
Unit II: Structure of Atom
Unit III: Classification of Elements and Periodicity in Properties
Unit IV: Chemical Bonding and Molecular Structure
Unit V: States of Matter: Gases and Liquids
Unit VI: Chemical Thermodynamics
Unit VII: Equilibrium
Unit VIII: Redox Reaction
Unit IX: Hydrogen
Unit X: s -Block Elements (Alkali and Alkaline Earth Metals)
UNIT XI: P -BLOCK ELEMENTS (CARBON AND BORON FAMILY)
UNIT XII: ORGANIC CHEMISTRY-BASIC PRINCIPLES AND TECHNIQUES
UNIT XIII: HYDROCARBON
UNIT XIV: ENVIRONMENT CHEMISTRY

Scientific Notation

In which any number can be represented in the form  N \times 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  232.507 as  2.32507 \times 10^2 in scientific notation.

Similarly  0.00007   can be written as  7 \times 10 ^{-5} .

Precision

Precision refers to the closeness of various measurements of some quantity.

Accuracy

Accuracy is the agreement of a particular value to the true value of the result.

Significant Figures

The reliability of measurement is indicated by the number of digits used to represent it. To express it more accurately we express it with digits that are known with certainty. These are called Significant Figures. They contain all certain digits plus one doubtful digit in a number.

Rules for Determining the Number of Significant Figures

 \to All non-zero digits are significant

e.g.  6.9   has two significant figures.

1.73  has three significant figures.

The decimal place does not determine the number of significant figures.

\to A Zero becomes significant in case it comes in between non-zero numbers.

e.g 1.005  has four significant figures.

3.09   has three significant figures.

 \to Zeroes at the beginning of a number are not significant.

e.g  0.0007 has one significant figure.

0.0077  has two significant figures.

\to All Zeroes placed to the right of a number are significant.

e.g.  23.00 has four significant figures.

 5.0 has two significant figures.

\to In exponential notations, the numerical portion represents the number os significant figures.

e.g.  0.00079 is expressed as  7.9 \times 10^{-4} .

 The number of a significant figures is  2 .

 \toThe decimal point does not count towards the number of significant figures.

Retention of Significant Numbers: Rounding Off Numbers

\to   If the digit coming after the desired number of the Significant figures happens to be more than  5 , the preceding significant figure is increased by one.

e.g. 4.516 is rounded off to  4.52.

\to If the digit involved is less than  5, it is neglected and the preceding significant figure remains unchanged.

e.g. 7.314   is rounded off to  7.31

 \to If the digit happens to be  5 , the last mentioned or preceding figure is increased by one only in case it happens to be odd. In case of even figure, the preceding digit remains unchanged.

e.g.  7.365 is rounded off to 7.36

 7.375 is rounded off to  7.38.

 

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