SOME BASIC CONCEPTS OF CHEMISTRY -CLASS 11-PURE NCERT BASED NOTES -HELPFUL FOR IIT JEE and NEET and any OTHER EXAM- CHEMISTRY CHP 1

 

DEFINITION OF CHEMISTRY - 

                              The branch of science that studies the preparation, properties, structure and reactions of materials substances called chemistry it is the science of molecules and their transformation.

DEVELOPMENT OF CHEMISTRY -

• Chemistry was developed mainly in form of Alchemy and Iatochemistry during 1300- 1600 CE.          
• Modern Chemistry to kept in 18th century Europe after a few centuries of alchemical traditions which were introduced by the Arabs.       
• In ancient India, chemistry was called Rasayan Shastra ,rastantra, Ras Priya and  Ras Vidya . It included metallurgy medicine manufacturer of cosmetics, glass ,etc.  
• Chemistry is also called science of atoms and molecules.

IMPORTANCE OF CHEMISTRY-

• Chemistry plays a central role in Science and is open Interruined with other branches of science.      
• Principles of chemistry are applicable in diverse areas such as weather patterns, functioning of brain, and operation of a computer, production in chemical Industries, manufacturing fertilizers, alkalis, acid ,salt ,soap, detergent and many more.       
• Chemistry contributes to a large extent to development and growth of nation and national economy.
• It also plays an important role in meeting human needs for food Health Care production and other materials.

MATTER

Anything which has mass and occupies space is called matter.

STATES OF MATTER -

•  Solid - 1.  Particles are held very close                         and tightly to each other and                         there is nothing much freedom                     of movement.                                               2. They have definite volume and                      shape.
• Liquid- 1. Particle are close to each other                    but they can move around.                           2. They have definite volume but.                   do not have definite shape .                          They take the shape of the                              container in which they are                            placed.
• Gases-  1. The particles are far apart to                        each other as compared to in                       solid and liquid and their                                movements is easy and fast.                      2. Gases have neither definite                            volume not definite shape the                       completely occupy the shape in                     their container in which they are                    placed.

These States of matter in convertible by changing the conditions of temperature and pressure.

CLASSIFICATION OF MATTER :-

Matter can be classified into mixture and pure substances. Mixture can be further classified into how much genius mixture and heterogeneous mixture and pure substances can be further divided into elements and compounds.

     Mixture contains particles of two or more pure substances which may be present in it in any ratio whereas, pure substances is when all constituent particles of a substance are same in chemical nature.

• The constituents of a compound cannot be separated into simpler substances by physical methods but can be by chemical method.
• The properties of compound at different from those of its constituent elements. For example, hydrogen and oxygen are gas  but their compound, water is a liquid. Hydrogen burns with a pop up sound and oxygen is a supporter of combustion but water is used as fire extinguisher.

PROPERTIES OF MATTER AND THEIR MEASUREMENT 

 Every substances unique or characteristic property which can be classified into two categories.

1. Physical properties - Includes colour  odour, melting point, boiling point,density etc. It can be measured observed without changing the identity or composition of the substances.

2. Chemical properties - Includes composition, combustibility, reactivity etc.  The measurement observation of chemical properties required a chemical change to occur.

MEASUREMENT OF PHYSICAL PROPERTIES -

• Two different system of measurement that is the English system and the metric system were being in used in different parts of world.
• The metric system was originated from France in late 18th century and was based on decimal system.

     The intentional system of unit (S. I.) 

• The international System of units (French Le systeme International d' unites- abbreviated as S. I unit)  was established by eleventh general conference on weights and measures.
• The  CGPA is an international governmental Treaty organisation created by a diplomatic Treaty known as Metre convention which was signed in Paris in 1875.
• The SI system has seven base units.

 Mass and weight

• Mass of a substance is the amount of matter present in it, whereas, weight is the force exerted by gravity on an object.
• Mass of an object is constant whereas weight of an object may vary from one place to another due to change in gravity.
• SI unit of mass is kg that is kg and SI unit of weight is Newton or kg metre per second square.

Volume 

• It is the amount of space occupied by a substance.
•  Its unit is length cube ,that is metre cube . Sometimes for small measurement it is denoted in centimetre cube or decimeter cube. 
• L is a common but not as a unit of used for measurement of volume of liquid.
• 1 litre is equal to 1000 ml.
• 1000 cm cube is equal to 1 decimeter cube.

Density 

• Density of a substance is it amount of mass per unit volume.
• It tell us about how closely its particle are packed. If density is more it means particles are more closely packed.
• Density = mass/ volume.
• Sometime density is expressed in gram centimetre per cube for smaller measurement.

Temperature

• Its SI unit is kelvin (K). 
• There are three scales to measure temperature- degree Celsius ,degree Fahrenheit and degree Kelvin.
• Generally ,the thermometer with degree Celsius are calibrated from zero degree to 100 degree where these two temperature and freezing and boiling point of water.
• Fahrenheit scale is represented between 32 degree to 212 degree.

Scientific notation 

• Scientific notation is a form in which any number can be represented in the form N×10 to the power n ,Where n is an exponent having positive or negative values and Nis a number which values where is between 1.0000..... and 9.0000........

Significant figures 

• Significant figures are meaningful digits which are known with certainty + 1 which is estimated or uncertain. The uncertainty is indicated by writing the certain digits and the last uncertain digit.

Rules for determining the number of significant figure:--

1. All non zero digit are significant. eg , in 285 CM there are three significant figure. 
2. Zeros preceding to first non zero digit are not significant . Thus,  0.03 has one significant figure.
3. Zeros between two non zero digit are significant. Thus 2.005 has four significant figure.
4. Zeros at the end a right of a number are significant provided they are on the right side of decimal point. Examples 0.002 gram has three significant figure.
5. Counting numbers of objects . For example, 2 balls or 20 eggs have infinite significant figures as these are exact numbers and can be represented by writing infinite number of zeros after placing a decimal that is two equal to 2.0000.....

Precision-  It refers to the closeness of various measurements for the same quantity.

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

Addition and subtraction of significant figures.

The result can not have more visits to the right of the decimal point than either of the original number.

For example,

 if we add 12.11, 18.0 and 1.012 then we get, 31.12 2. But according to the law of addition or subtraction the result will 31.1.

Multiplication and division of significant figures.

In these   operations, the result must be reported with no more significant figure as in the measurements with few significant figures. 

Example-  2.5  × 1.25 = 3.125.

Rules for rounding off the numbers in significant figures.

1. If the rightmost digit to be removed is more than 5, the preceding number is increased by 1.
2. If the rightmost digit to be removed is less than 5, then the preceding number is not changed.
3. If the rightmost is it to be removed is 5, then the preceding number is not change if it is an even number but it is increased by 1 if it is an odd number.

DIMENSIONAL ANALYSIS

The method used to accomplish the conversion of units from one system to other is called factor level method or unit factor method or dimensional analysis.

Law of combination of chemical 

                          OR

law of chemical combination

According to this no matter can neither be created nor be destroyed. 

This law was put forward by Antonie Lavoisier in 1789.

Law of Definite proportion

A given compound always contains exactly the same proportion of elements by weight.

This law was given by French chemist Joseph Proust  who work on with two samples of cupric carbonate -one natural and other synthetic.

Law of multiple proportion

If two elements and combine ,to form more than one compound and masses of one element, that combined with a fixed mass of other elements, are in the ratio of small whole numbers.

This law was proposed by Dalton in 1803.

Gay lusaac's law of gasoues volume 

When gas is combined or produced by a chemical reaction they do so in a simple ratio by volume , provided all gases are at the same temperature and pressure.

This law was given by Gay Lussac in 1808 and it is actually the law of Definite proportion by volume.

Avogadro's law

Equal volume of all gases at the same temperature and pressure should not contain equal number of molecules.

Given by Avogadro in 1811.

DALTON'S ATOMIC THEORY 

POSTULATES 

1.  Matter consists of indivisible atoms.

2. All items of a given element have identical properties ,including identical masses fully stocked atoms of different elements differ in mass.

3. Compounds are formed when atoms of different elements combine in a fixed ratio.

4. Chemical reactions involved rearrangement of atoms. These are neither created nor destroyed in a chemical reaction.

DRAWBACKS

1. Dalton's theory could not explain the laws of chemical combination ,however, it could not explain the laws of gaseous volumes.

2. It could not provide reasons for combining of atoms which was answered later by other scientists.

Atoms and molecules masses

Atomic mass

• The system of atomic mass or mass of atom is based on Carbon 12 as the standard and has agreed upon in 1961.
• Carbon- 12  is the isotope of carbon represented as 12c . Here, 12 C is assigned as mass of exactly 12 atomic mass unit (AMU) and masses of all other atoms are given relative to the standard.
• In earlier times hydrogen being the lightest Atom was arbitrarily assigned as the mass of one without any unit and other elements were assigned mass relative to it.
• One atomic mass unit is defined as a mass exactly equal to one twelfth of the mass of one carbon 12 atom.
• Nowadays, atomic mass unit has been replaced by 'U' which is known as unified mass.

Molecular mass 

• Molecular mass is the sum of atomic masses of the elements present in a molecule.
• It is obtained by multiplying the atomic masses of each element by number of its atoms and adding them together.

Mole concept and molar masses

• In SI system ,mole was introduced as seventh base quantity for amount of a substance.
• 1 mole is the amount of a substance that contains as many particles or entities as there are atom in exactly 12 gram of carbon isotope.
• Mole of a substance always contains the same number of entities  no matter what substance maybe.
• One mole of carbon atoms weighs 12 grams the number of atoms in it is equal to 6.0 to 21367 into 10 to the power 23 atoms or molecules.
• The mass of one mole of substance in G is called its molar mass numerically equal to atomic and molecular formula mass.

Percentage Composition

Mass % of  an element =  mass of that element                                               in compound/ molar                                                   mass of the                                                               compound×100.

Empirical formula for molecular formula

• And empirical formula represents the simplest whole number ratio of areas atoms present in a compound whereas the molecular formula shows the exact number of different types of atoms present in a compound.

Stiochiometry and stoichiometric calculations

 It deals  with the calculations of volume of masses of reactants involved in a chemical reactions.

                It was derived from Greek word 'stoichein' meaning element and 'metron' meaning measure.

Relationship of mass volume and density

    MASS/VOLUME= DENSITY

Limiting reagent

• Limiting reagent is the reactant that is used up completely . This stop the reaction and no further the products are made.
• One way to determine the limiting reagent is to compare the mole ratio of the amount of reactants used.

Reactions in solutions

• The concentration of a solution or the amount of substance present in a given volume can be expressed in any of the following ways-

1. Mass percent or weight percent=  Mass of solute /Mass of solution ✕ 100
2. Mole fraction . It is the ratio of a number of moles of a particular component to the total number of moles of the solution.
3. Molarity. It is the mostly used unit and denoted by 'M'.   It is defined as the number of moles of the solute in one litre of the solution.
4. Molality. It is defined as number of moles of solute present in 1 kg of solvent. Denoted by 'm'.