chemical bonding and molecular structure

Molecule :

A group of atoms is found to exist together as one species having characteristic properties. Such a group of atoms is called a molecule.

Chemical Bond :

The attractive force which holds various constituents (atoms, ions, etc.) together in different chemical species is called a chemical bond.

KÖSSEL-LEWIS APPROACH TO CHEMICAL BONDING :

Lewis given the concept of stable valence  shell by considering nucleus and inner electron as a kernel  and outermost shell around it.so that all eight electron occupy

eight corners of cubic lattics and outermost shell tend to get inert gas configuration by gaining or losing electrons.Lewis also postulated that atoms achieve the

stable octet when they are linked by chemical bonds

Lewsis symbols :

Valence electrons : In the formation of a molecule, only the outer shell electrons take part in chemical combination and they are known as valence electrons.

Lewis has given symbol method to represent outermost shell of all elements of periodic table for example :-

Lewsis symbols for elements of second period is given below :

significance of lewis symbols :

The dots represent number of valence electrons and it helps to calculate group valence electrons

Group Valence electrons :

The group valence of the elements is generally either equal to the number of dots in Lewis symbols or 8 minus the number of dots or valence electrons.

Kössel, in relation to chemical bonding,drew attention to the following facts:

• In the periodic table, the highly electronegative halogens and the highly electropositive alkali metals are separated by the noble gases.

• The formation of a negative ion from a halogen atom and a positive ion from an alkali metal atom is associated with the gain and loss of an electron by the
respective atoms.

• The negative and positive ions thus formed attain stable noble gas electronic configurations. The noble gases (with the exception of helium which has a duplet
of electrons) have a particularly stable outer shell configuration of eight (octet) electrons, ns2np6.

• The negative and positive ions are stabilized by electrostatic attraction.

Let us take example of formation of Nacl:-

Electrovalent Bond :

The bond formed, as a result of the electrostatic attraction between the positive and negative ions was termed as electrovalent bond.The electrovalence
is thus equal to the number of unit charge(s) on the ion.

Octet Rule :

According to this,atoms can combine either by transfer of valence electrons from one atom to another (gaining or losing) or by sharing of valence electrons in order to have an octet in their valence shells. This is known as octet rule.

Covalent Bond :

Sharing of electron to attain noble gas configuration leads to formation of covalent bond.for example chlorine formed by sharing a pair of electron among two chlorine atoms

The dots represent electrons. Such structures are referred to as Lewis dot structures.

The important conditions Lewis dots are :
• Each bond is formed as a result of sharing of an electron pair between the atoms.

• Each combining atom contributes at least one electron to the shared pair.

• The combining atoms attain the outershell noble gas configurations as a result of the sharing of electrons.

If two atoms share two pairs of electrons, the covalent bond between them is called a double bond

When combining atoms share three electron pairs as in the case of two nitrogen atoms in the N2 molecule and the two carbon atoms in the ethyne molecule, a triple bond is formed.

Previous year question paper

Chemistry Class 11 Previous Year Question Papers

Chemistry Class 12 Previous Year Question Papers

Some basic concepts of chemistry

Chemistry :

chemistry is the branch of science which deals with the composition ,structure and properties of matter.

Branches of chemistry :

Inorganic chemistry :

Inorganic chemistry deals with the synthesis and behavior of inorganic and organometallic compounds or it is the study of

elements other then carbon and its compounds.

organic chemistry:

organic chemistry is the branch of chemistry in which we study about organic compounds or the substances produced by organic compounds.

Physical chemistry :

Physical chemistry is the study of macroscopic, atomic, subatomic, and particulate phenomena in chemical systems in terms

of the principles, practices and concepts of physics such as motion, energy, force, time, thermodynamics, quantum

chemistry, statistical mechanics, analytical dynamics and chemical equilibrium.

Analytical chemistry :
It is  the branch of chemistry which deals with qualitative analysis of chemical substances.

In additions to these branches their are many other branches like nuclear chemistry,biochemistry etc.

Matter :
Anything which occupies space and have some specific mass is call matter.

Classification of matter :

Physical classification :

solid :- Solid have particles arranged very closeley so they have definite volume and shape

liquid :- Liquid have closed packed arrangement of particles but particles are free to move anywhere so liquid have definite volume but not definite shape.

Gas :- Gases have particles losely held so they do not have definite shape and definite volume.so gases have no definite shape and definite volume

Chemical Classification :
Chemically their are two types of substances present i.e pure substance and mixtures which can be further classified as

given below :-

Pure substances :-

a)elements  :

It is the simplest form of pure substance which can be neither decomposed, divided or built  by simple chemical or

physical methods and it only one kind of atoms

an element is of three typees i.e metal ,non metal and mettaloids.till now 118 elements are known ,hydrogen is the most

abudant element in the universe and oxygen in the most abudant non metal in the earth crust



b)compounds :
compound is a form of matter which can be formed by combining two or more elements in a definite ration by mass.It can be

divided or separated by suitable chemical reaction.
compound can of two types :-

organic and inoragnic

Organic compounds :

Organic compunds are hydrides of carbon earlier it was considered to be formed by living organism like plant and animals.

Inorganic compounds :

Inorganic compounds are the compound of all element except hydries of carbon ealier it was considered as it is derived from inorganic materials like rock and minerals.

Symbols :

a symbol is an abbreviation or shortened form for the full name of an element,,all the elements have some symbols to

represent them.like

sodium have Na,potassium have k ,copper has cu irin has Fe etc.

Mixtures :

Mixture are made up of two or more substances they can possess variable composition and can be seprated into their components by some physical methods.

it is of two types homogeneous in which composition is uniform throughout and hetrogeneous in which composition is not uniform throughout

Filtration :

filtration is the process of seprating solids which are suspended in liquids with the help of filter funnel when mixture passes through the filter funnel solid remain intact with it and liquid passes.

Distillation :

Distillation is the process of heating liquid to form vapours then collecting vapours and cooling vapours to get back the liquid.

Sublimation :

This is the process of conversion of solid directly into vapours on heating.

Magnetic sepration :

This process is based on the magnetic property of a substance as a magnet attracts magnetic substance of the mixture when it is placed in front of mixture.

Crystallisation :
It is the process of separating solids having different solubilities in a particular solvent.

Atmolysis :

This method based on rates of diffusion of gases and used for their separation of gases

Atoms and molecules :-

Atom is the smallest particle of an element which not be further divided.It may or may not capable of independent existence.

Molecule is the simplest particlenof matter that has independent existence.

Physical Quantities and Their Measurement :

Units are of two types

1)Basic unit :

Fundamental unit are length(m),mass(kg),time(s),electric current(A).thermodynamic temparature(K),amount of substance(mol) and luminous intensity(cd)

2)Derived units : Derived units are derived from fundmental unit example unit of density derived from units of mass and volume.

Various physical quantities are :

a)CGS System :
It is based on centimetre,gram and second as the units of length,mass,time

b)FPS System :

foot,pound,second used as the fundamental units

c)MRS System :

metre,kilogram and second used for measurements

d)SI system :

International system of units :-

PHYSICAL QUANTITY                  Name of S.I UNIT
Length(l)                                             metre
Mass(m)                                              Kilogram
Time(t)                                                 second
Electric current(i)                                 ampere
Thermodynamic temprature(T)            Kelvin
Amount of substance(n)                        mole
Luminous intensity(ly)                          candella

Significant figures :

significant figures are meaningfull digits which are known with certainity.The uncertainity is indicated by writing

the certain digits and the last uncertain digit.

it means in many calculations in which we get slightly different digits,you can say minute difference digits or result

its very neccessary to get accurate result so to get accrate result we take help of significant figures.for example:

suppose we are measuring something and it comes out to be 11.999999 first time and then again 11.999996 second time,so to get accurate result we have take care of significant figure in this example 11 is certain digit while 999996 or 999999 is uncertain digit.

Rules for determining significant figures :

1)All non zero digits are significant. for example in 365 and .456 their are three significant figures

2)Zeros preceding to first non zero digit are not significant .example 0.98 has two significant figure,0.03 has one significant figure.

3)zeros between two non zero digits are significant.example 2.009 has four significant figure.

4)zeros at the end or right of a number are significant provided they are on the right side of the decimal point. for example 0.300 has three significant figures.

5)Exact numbers have an infinite number of significant figures.for example 3 and 30 have infinite significant figures,as 3 can be written as 3.0000.... and 30 can be writeen as 30.000000...... when we write numbers in scientific notation like 3.02 x 10² the number between 1 to 10 gives number of significant figure for example in 3.02 x 10² has three significant figures.

Addition and subtraction of significant figures :

Result cannot have more digits to the right of the decimal point than either of the original numbers.

for example when we add  13.56
                         19.0
                         --------
                          32.56
                         ---------

19.0 has only one digit after the decimal point and the result should contain only one digit after the decimal point.

Multiplication and division of significant figures :

In this also result should not contain more significant figures then any of the numbers for example

2.5 x 1.25=3.125  since 2.5 has two significant figures so result should be 3.1

Rules for rounding of the numbers :

1)If the rightmost digit to removed is more than 5 then preceding number increased by one.
for example 1.457 can be rounded off to 1.46

2)If the rightmost digit to removed is less than 5 then preceding number decreased by one.
for example 1.457 can be rounded off to 1.45

3)If the rightmost digit to removed is equal to 5 then we check the preceding number that it is odd or even and if preceding number is odd then it is increased by one and if it is even the number remain same.
for example : 1.45  can be rounded off to 1.4 and 1.35 can be rounded to 1.4


Law of chemical combination :
Their five basic laws which govern formation of compound with the help of elements.

Law of conservation of mass (Lavoisier,1774) :

This law states that during any physical or chemical change the total mass of the products is equal to the total mass of reactants.It does not hold good for nuclear

reactions.

Law of definite proportions (Proust,1799) :

According to this law a chemical compound obtained by different sources always contains same percentage of each constituent element.


Law of multiple proportions (Dalton,1803) :


According to this law if two elements can combine to form more then one compound,the masses of one element that combine with a fixed mass of the other element are in

the ratio of small whole numbers


Gay Lussac law of gaseous volumes :

when gases combine or produced in a chemical reaction they do so in a simple ratio by volume provided all gases are at same temperature and pressure.

Avogadro Law :

Equal volumes of gases at the same temperature and pressure should contain equal number of molecules.
for example : Two volume of hydrogen combine with one volume of oxygen to form two volume of water vapour

Dalton atomic theory :-

1. Matter consists of indivisible atoms.

2. All the atoms of a given element have identical properties including identical mass. Atoms of different elements dffer in mass.

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

4. Chemical reactions involve reorganisation of atoms. These are neither created nor destroyed in a chemical reaction.
Dalton’s theory could explain the laws of chemical combination.

Atomic and molecular masses :

One atomic mass unit is defined as a mass exactly equal to one twelfth the mass of one carbon - 12 atom.
And 1 amu = 1.66056×10^–24 g

Today, ‘amu’ has been replaced by ‘u’ which is known as unified mass.

In general for elements we take avaerage atomic mass as an elements can contain many form like carbon has three isotopes c-12,c-13,c-14  so we have to take average of these

Molecular mass :

Molecular mass is the sum of atomic masses of the elements present in a molecule

for example : Molecular mass of methane,
(CH₄) = (12.011 u) + 4 (1.008 u)
= 16.043 u

Formula mass :

The formula such as NaCl is used to calculate the formula mass instead of molecular mass as in the solid state sodium
chloride does not exist as a single entity.

Thus, formula mass of sodium chloride =atomic mass of sodium + atomic mass of chlorine= 23.0 u + 35.5 u = 58.5 u

Mole concept and molar masses :

One mole is the amount of a substance that contains as many particles or entities as there are atoms in exactly 12 g (or 0.012kg) of the 12C isotope.

so 12C carbon atom is taken as base for calculation of mole ,so any substance one mole quantity will be equal to the entities present in 12C atom.

mass of a C-12 carbon atom =1.992648
and we know that one mole of carbon weighs 12g we can calculate number of atoms present in it:

=12/1.992648
=6.0221367

this number is called Avogadro number

Molar masses :-

The mass of one mole of a substance in grams is called its molar mass.

NCERT Solutions

NCERT SOLUTIONS OF CLASS 12 CHEMISTRY

NCERT SOLUTIONS OF CLASS 11 CHEMISTRY

chemistry class 12 ncert solutions

NCERT Solution of  Chapter 1 The Solid State

NCERT Solution of  Chapter 2 Solutions

NCERT Solution of  Chapter 3 Electrochemistry

NCERT Solution of  Chapter 4 Chemical Kinetics

NCERT Solution of  Chapter 5 Surface Chemistry

NCERT Solution of  Chapter 6 Principal and Processes of Isolation of Elements

NCERT Solution of  Chapter 7 The P-Block Elements

NCERT Solution of  Chapter 8 The d and f Block Elements

NCERT Solution of  Chapter 9 Haloalkanes and Haloarenes

NCERT Solution of  Chapter 10 Alcohols, Phenols and Ethers

NCERT Solution of  Chapter 11 Aldehydes, Ketones and Carboxylic Acids

NCERT Solution of  Chapter 12 Amines

NCERT Solution of  Chapter 13 Polymers

NCERT Solution of  Chapter 14 Biomolecules

NCERT Solution of  Chapter 15 Chemistry in Everyday Life

chemistry class 11 ncert solutions

NCERT Solution of  Chapter 1 Some Basic Concepts of Chemistry

NCERT Solution of  Chapter 2 Structure of Atom

NCERT Solution of  Chapter 3 Classification of Elements and Periodicity in Properties

NCERT Solution of  Chapter 4 Chemical Bonding and Molecular Structure

NCERT Solution of  Chapter 5 States of Matter

NCERT Solution of  Chapter 6 Thermodynamics

NCERT Solution of  Chapter 7 Equilibrium Part

NCERT Solution of  Chapter 8 Redox Reactions

NCERT Solution of  Chapter 9 Hydrogen

NCERT Solution of  Chapter 10 The S-Block Elements

NCERT Solution of  Chapter 11 The P-Block Elements

NCERT Solution of  Chapter 12 Organic Chemistry – Some Basic Principles and Techniques

NCERT Solution of  Chapter 13 Hydrocarbons

NCERT Solution of  Chapter 14 Environmental Chemistry

Classification of elements and periodicity of properties

Classification of elements :-

As the number of elements are very much in counting and many resembles and exhibit same properties so studying all without any classification will be a difficult task so to make study easier classification was done.

many attempts were made for classifying the elements some are given below:-

Prout's Hypothesis (1815) :-

It is also known as unitary method according to it hydrogen atom was considered as the fundamental unit from which all other atoms were made.

Dobereiner's Triads (1829) :-

Dobereiner classified elements into group of 3 of similar properties in which atomic weight of middle was arithmetic mean of other two.

Dobereiner could not able to arrange all elements he had found only three triads so this theory failed.

Newland Octaves (1864 law of octaves) :-

It states that when elements are arranged in order of increasing atomic masses,every eight element has properties similar to the first just like in the musical note.

Limitations:-

This classification was not successfull beyond calcium
After the discovery of noble gases their arrangement disturbed the whole configuration

Lother Meyer's Atomic volume curve (1869) :-

It classified the elements in the form of a curve between atomic volume and atomic masses and state that properties of elements are the periodic functions of their atomic masses & concluded that elements with similar properties occupy similar position in the curve.

Mendeleef Periodic Table :-

The physical and chemical properties of the elements are a periodic function of their atomic masses and their were only 63 elements discovered at the time of Mendeleev. The periodic table is suppose to consist of seven horizontal periods and eight vertical columns,zero group added later in the Mendeleev periodic table.

Importance of Mendeleev periodic law :-

a)He has done a proper and systematic arrangement of elements.

b)He left the space for some undicovered elements e.g: he left the space for Ga and Ge and named these elements as ERa-Aluminium(Ga) and EKa-silicon (Ge)

c)He has also done atomic mass correction of doubtful elements on the basis of their expected positions and properties.

Defects of Mendeleev periodic Table :-

a)Position of hydrogen :-

Position of hydrogen is doubtfull as it is placed in group IA(Alkali metal) but it also shows resemblance with halogens of group VIIA,so its position in Mendleev periodic table is doubtfull

b)Position of Isotopes :-

As Mendeleev periodic table was based on atomic weight so isotopes of an element should occupy different positions which is not true.

c)Anomalous positions of some elements :-
In some situation elements with higher atomic mass precedes the element with lower atomic mass like AL atomic weight=39.9 precedes K which is having atomic weight 39.1

d)Position of Lanthanoids and actinoids :-

They both are not placed in main periodic table
odern Periodic Law :- It states that " Physical and chemical properties of elements are the periodic function of their atomic numbers " He also observed that when elements are arranged in order of increasing atomic numbers their properties repeats after some regular intervals like 0,1,2,8,8,18 and 32.These numbers are called magic numbers and cause perodicicty due to repetition of similar electronic configuration. Features of long form of Periodic table :- a)It has 18 groups and 7 periods .

Features of long form of Periodic table :-

It has 18 groups and 7 periods
First period(H-He) conatins 2 elements and it is the smallest period.

Second Period(Li-Ne) contains 8 elements

Third Period(Na-Ar) contains 8 elements

Fourth Period(K-Kr) contains 18 elements
Fifth Period(Rb-Xe) contains 18 elements

Sixth Period(Cs-Rn) contains 32 elements

Seventh Period(Fr) contains 19 elements,it is incomplete

elements of group 1 are called alkali metals ,group 2 are called alkaline earth metals ,elements of group 16 are called chalcogens,group 17 are called halogens and group 18 are called noble gases

S Block Elements

In S block the electron enters in the s-orbital.As the s block element can accommodateonly two electrons so s block elements have two groups ,group 1 and 2 .

Group 1 elements consists of  lithium, sodium, potassium, rubidium, caesium and  francium and collectively known as the alkali metals.

Group 2 element consist of  beryllium, magnesium,calcium, strontium, barium and  radium. Except Beryllium they are known as alkaline

The general electronic configuration is ns^1-2

Alkali Metal  :-

Group 1 element have one electron in their valence shell,they are reactive and soft so they do not occur in their native state.As their oxides and hydroxides form strong alkalies like NAOH,KOH etc these are also know as alkali metals,lithium is known as bridge element.

 General characterstics of Alkali metals:-

1)Electronic configuration  :-
Element =Li ,atomic number=3 and electronic configuration=[He]2s¹

Element =Na ,atomic number=11 and electronic configuration=[Na]3s¹

Element =K ,atomic number=19 and electronic configuration=[K]4s¹

Element =Rb ,atomic number=37 and electronic configuration=[Rb]5s¹

Element =Cs ,atomic number=55 and electronic configuration=[Cs]6s¹

Element =Fr ,atomic number=87 and electronic configuration=[Fr]7s¹

2)Atomic Radii :-

The atomic radii of alkali metals are biggest in their respective periods and it increases as we move down the group and all these form lattice with cordination number =4

3)Ionic Radii :-
Ionic radii increases down the group due to addition of a new energy subshell and ionic radii of alkali metals are much smaller than their corresponding metals due to lesser number of shells and contraction of increased nuclear charge.

4)Density :-It increases on moving down the group.Li is the lightest known metal.The density of potassium is lesser than sodium due to abnormal increase in size on moving down the group from Na to K

5)Melting and Boiling Point :-

melting and boiling point dcreases down the group due to weak mettalic bond as we go down,Fr is liquid at room temperature

6)Softness :-

These are soft ,malleable,ductile and having lusture,it can also be cut with knife.

7)Atomic Volume :-

Atimic volume is highest of alkali metal in their respective period and it increases down the group.

8)Ionisation Enthalpy :-

The first ionisation enthalpy is low for alakali metal ,but second ionisation enthalpy is very high as by losig one electron it aquires noble gas configuration.so removal of second electron is very difficult.

9)Electropositive character :-
Due to low ionisation enthalpy alakali metals are very electropositive or mettalic in nature it increases down the group due to increase in enthalpy.

10)Oxidation state :-

Alkali metals show oidation state +1 as they form noble gas configuration by losing one electron.

11)Hydration of ions :-

It decrease down the group,smaller is the size of cation greater is its hydration enthalpy

12)Flame coloration :-

All the alkali metals give flame coloration as they have one valence electrons in the outermost shell so it easily get excited to higher energy level and when it returns to lower energy level it releases visible light of characteristic wavelength which provides color to flame all the metals provide different colors that are:-

Li- crimson red
Na- yellow
K- violet
Rb - red violet
Cs - Blue
13)Photoelectric effect :-

As ionisation enthalpy is low for alakli metals so it ejects electron when exposed to light easily specially "cs"
so all exhibit photoelctric effect.

14)Electrical Conductivity :-

Due to the presence of loseley held electron ,all the alakli metals are good conductor of electricity.electrical conductivity increases from top to bottom.

15)Reducing character :- As the ionization energy is low for alkali metals so it has good reducing power and the order is given below:-

Na<K<Rb<Cs<Li

Chemical properties of alakli metals :-

 1)Action of air :- They form oxides,hydroxides and carbonates on exposure to moist air and their surface gets tarnished.
Due to their reactivity they are kept under kerosene oil or paraffin wax ,as lithium has lowest density so its floats on the surface of inert liquids like kerosene oil so it is wrapped in paraffin wax.CCl₄ is used to extinguish fire occurred by alkali metals.

 4Na(s) + o₂(g)----> 2Na₂o(s)
Na₂o(g) + H₂ O(l) -----> 2NaOH(s) 2NaOh(s) + CO₂(g) -----> Na₂Co₃(s)
Na₂o(g) + Co₂(l) -----> 2NaOH(s) 2NaOh(s) + CO₂(g) -----> Na₂Co₃(s)

 2)Action of oxygen :-

 All the alkali metals react with oxygen to form different types of oxides some form oxides and some form super oxide e.g lithium forms lithium oxide(Li₂),sodium forms sodium peroxide(Na₂O₂), while rest form super oxides which is KO₂,RbO₂,CsO₂ The stability oxides and super oxides increases as the size of alkali metal increases. Ko₂ (Potassium super oxide) is used as a source of oxygen in submarines,space shuttles and in emergency breathing apparatus such as oxygen masks.

3)Action of water or compounds containing acidic hydrogen :-

2M +H₂O ----->2MOH + H₂O (Where M = Li, Na,K,Rb and Cs )

reactivity order with water is given below it increase from top to bottom due to increase in electropositive character :-

Li<Na<K<Rb<Cs

LiOH is used to remove carbon dioxide from exhaled air in confined quarters like submarines and space vehicles.


4)Action of Hydrogen :-

The reactivity with hydrogen decreases down the group and the order is given below:-

Li>Na>K>Rb>Cs

2M + H₂O -----> 2MH (Where M = Li,Na,K,Rb and Cs)

5)Reaction with Halogens :-

Alkali metals combines fast with halogens to form ionic halides with the exception of some lithium halides.The order of reactivity given below:-

Li<Na<K<Rb<Cs

2M + XH₂O ----> 2M⁺XH^- (where M = Li,Na,Ketc and X = F,Cl,Br,I

Bigger the anion larger will be polarisability therefore covalent character will be in order given below :-
LiI>LiBr>LiCl>LiF

3)Action of water or compounds containing acidic hydrogen :-

2M + 2H₂O ----->2MOH + H₂ (Where M = Li, Na,K,Rb and Cs )

reactivity order with water is given below it increase from top to bottom due to increase in electropositive character :-

Li<Na<K<Rb<Cs

LiOH is used to remove carbon dioxide from exhaled air in confined quarters like submarines and space vehicles.


4)Action of Hydrogen :-

The reactivity with hydrogen decreases down the group and the order is given below:-

Li>Na>K>Rb>Cs

2M + H₂O -----> 2MH (Where M = Li,Na,K,Rb and Cs)

5)Reaction with Halogens :-

Alkali metals combines fast with halogens to form ionic halides with the exception of some lithium halides.The order of reactivity given below:-

Li<Na<K<Rb<Cs

2M + X₂ ----> 2M⁺X^-(where M = Li,Na,Ketc and X = F,Cl,Br,I

Bigger the anion larger will be polarisability therefore covalent character will be in order given below :-
LiI>LiBr>LiCl>LiF

6) Solubility in liquid ammonia :- All alkali metals forms a blue solution on reaction with ammonia ,the blue color is due to ammoniated metal cations and ammoniated electrons in the solution.
The blue color is due to the excitation of ammoniated electron to higher energy levels and the solution is highly conducting and para magnetic due to the presence of ammoniated cation and anion

 M + (x + y)NH₃ -----> [M(NH₃)_x]⁺ (ammoniated cation) + [e(NH₃)_y)]^-    (ammoniated electron)

Orbital and Electronic configuration

Orbital:-

An orbital is a mathematical function that describes the wavelike behavior of an electron, or describes properties characteristic of no more than two electrons in the vicinity of an atomic nucleus or of a system of nuclei as in a molecule. An orbital often is depicted as a three-dimensional region within which there is a 95 percent probability of finding the electron ( Although most people think of an "orbit" in terms of a circle, the probability density regions that may contain an electron may be spherical, dumbbell-shaped, or more complicated three-dimensional forms.

Chemistry Notes For class 11

Unit 1.Some Basic Concepts of Chemistry

Unit 2.Structure of Atom

Unit 3.Classification of Elements and Periodicity in Properties

Unit 4.Chemical Bonding and Molecular Structure

Unit 5.States of Matter

Unit 6.Thermodynamics

Unit 7.Equilibrium Part

Unit 8.Redox Reactions

Unit 9.Hydrogen

Unit 10.The s-Block Elements

Unit 11.The p-Block Elements

Unit 12.Organic Chemistry – Some Basic Principles and Techniques

Unit 13.Hydrocarbons

Unit 14. Environmental Chemistry

Classes

Chemistry Notes For Class 11

Chemistry Notes For Class 12

Class 11 Chemistry Topics :-

Chapter 1: SOME BASIC CONCEPTS OF CHEMISTRY :

• understand and appreciate the role of chemistry in different spheres of life

• explain the characteristics of three states of matter

• classify different substances into elements, compounds and mixtures

• define SI base units and list some commonly used prefixes

• use scientific notations and perform simple mathematical operations on numbers

• differentiate between precision and accuracy

• determine significant figures • convert physical quantities from one system of units to another

• explain various laws of chemical combination

• appreciate significance of atomic mass, average atomic mass, molecular mass and formula mass

• describe the terms – mole and molar mass

• calculate the mass per cent of different elements constituting a compound

• determine empirical formula and molecular formula for a compound from the given experimental data

• perform the stoichiometric calculations.

Chapter 2 STRUCTURE OF ATOM :

know about the discovery of electron, proton and neutron and their characteristics

• describe Thomson, Rutherford and Bohr atomic models

• understand the important features of the quantum mechanical model of atom

• understand nature of electromagnetic radiation and Planck’s quantum theory

• explain the photoelectric effect and describe features of atomic spectra

• state the de Broglie relation and Heisenberg uncertainty principle

• define an atomic orbital in terms of quantum numbers

• state aufbau principle, Pauli exclusion principle and Hund’s rule of maximum multiplicity

• write the electronic configurations of atoms.

Chapter 3 :CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES :

• appreciate how the concept of grouping elements in accordance to their properties led to the development of Periodic Table.

• understand the Periodic Law; • understand the significance of atomic number and electronic
configuration as the basis for periodic classification

• name the elements with Z >100 according to IUPAC nomenclature

• classify elements into s, p, d, f blocks and learn their main characteristics;

• recognise the periodic trends in physical and chemical properties of elements;

• compare the reactivity of elements and correlate it with their occurrence in nature;

• explain the relationship between ionization enthalpy and metallic character;

• use scientific vocabulary appropriately to communicate ideas related to certain important properties of atoms e.g., atomic/ionic radii, ionization enthalpy, electron gain enthalpy, electronegativity,  valence of elements.

Chapter 4 : CHEMICAL BONDING AND MOLECULAR STRUCTURE :

understand KÖssel-Lewis approach to chemical bonding

• explain the octet rule and its limitations, draw Lewis structures of simple molecules

• explain the formation of different  types of bonds

• describe the VSEPR theory and predict the geometry of simple molecules

• explain the valence bond approach for the formation of covalent bonds

• predict the directional properties of covalent bonds

• explain the different types of hybridisation involving s, p and d orbitals and draw shapes of
simple covalent molecules

• describe the molecular orbital theory of homonuclear diatomic molecules

• explain the concept of hydrogen bond.

Solid state

Solids :-

Solids are the chemical substances which are characterized by define shape and volume,  rigidity, high density, low compressibility. The constituent particles (atoms, molecules or ions) are closely packed and held together by strong inter particle forces

Types of solids :-

Their are two types of solids :-
1)Crystalline solid
2)Amorphous solid

Difference between crystalline and amorphous solids :-

Crystalline solid	Amorphous solids
1 These have definite and regular arrangement of the constituent particles in space.	These doesn’t have any regular arrangement of the constituent particles in space.
2 These are true solids.	These are super cooled liquids or pseudo solids.
3 These have long order arrangement of the particles.	These have short order arrangement of particle.
4 These are anisotropic in nature, i.e., their physical properties are different in different directions.	These are isotropic in nature i.e., their physical properties are same in all the directions.
5 They have sharp melting points.	They melt over a certain range of temperature.
6 They undergo a clean cleavage when cut.	They undergo irregular cleavage when cut.

Types of crystalline solids:-

Character	Ionic solids	Covalent solids	Molecular solids	Mettalic solids
constituent particles	Positive and negative ions	Atoms	Molecules	Positive metals ions(kernels) and free electrons
Bonding Forces	Electrostatic Attraction	Covalent	Vander walls dipole dipole	electrostatic attraction between Positive ion and negative species
Melting Point	High Melting point	Very high melting point	Low melting point	Moderate to high melting point
Hard/Soft	Hard and Brittle	very hard	very soft	hard and soft
Conductance	Conductor in aqueous solution or in molten state	Non Conductor	Insulator conductor	Good conductor
Example	Nacl and Caf2	Diamond and silica	H2O and CO2	CU and FE

Structure determination by X-ray diffraction-Bragg's equation :-

Bragg equation states that there is a definite relationship between the angle at which a beam of X rays must fall on the parallel planes of atoms in a crystal in order that there be strong reflection, the wavelength of the X rays, and the distance between the crystal planes :  sin Θ = nλ / 2d where Θ is the angle between the incident or the reflected beam and the crystal plane, λ is the X-ray wavelength, d is the crystal plane separation, and n is any integer

Unit cell :-

The smallest geometrical portion of the crystal lattice which can be used as repetitive unit to

build up the whole crystal is called unit cell

Types of unit cell

1)Simple or primitive unit cell :-

In the simple unit cell particles are present only at the corners of the crystal :-

Number of atoms in simple cubic lattice is equal to 1 and can be calculated as below:-

 8 atoms are present at corner
so,Number of atoms = 8*1/8=1

2)Face centred unit cell :-

In this particles are present at corners as well as at every face of the crystal.

Numbers of atoms present in FCC:-

Number of atoms presnt at corners=8
Number of atoms present at the faces=3
  so total no atoms= 8*1/8+6*1/2=4

3)Body centred unit cell :-

In this particle are present at the corners as well at the body center
Number of atoms in BCC is eqaul to :-

Number of atoms presnt at corners=8
Number of atoms present in the body=1
  so total no atoms= 8*1/8=1+1=2

4)End centered unit cell :-

In this particles are present at all the corners of the crystal as well at the ends of crystal

Number of atoms present in end centered unit cell:-
Number of atoms presnt at corners=8
Number of atoms present at the ends=2
  so total no atoms= 1+1=2

Number of particle per unit cell of a crystal:-

Seven crystal system :-
There are about 230 crystal forms, which have been grouped into 14 types of space lattices,
called Bravais Lattices, on the basis of their symmetry and seven different crystal systems on
the basis of interfacial angles and axes.

Packing Fraction:-

1)Packing fraction in a simple cubic unit cell:-

Consider radius of sphere is = r
and Edge length of unit cell =a
As sphere are touching each other so edge lengt will be equal to 2r
                   
No. of sphere per unit cell= 1
Volume of sphere = 4/3πr3
Volume of cube =a3= (2r)3 = 8r3
Packing fraction (PF)=Percentage occupied = 52.4%

2)FCC Packing fraction:

3)BCC Packing Fraction:-

so packing fraction in Body centered unit cell = 68%

Cordination number:-



Void or space or holes

Density of unit cell

The structure of ionic crystals

Imperfections in solids

Point defects:-

1)Stoichiometric defect :-

In these defects equal number of cation and anion get missing from the crystal so the ratio of anion and cation remains same as the Stoichiometry of the substance not changed.
These are further classified as:
1)Vacancy defects: - These happens when some crystal site is vacant and it results in dcrese in density.
2)Interstitial Defects: - When some constituent particles present in the interstitial side, it increase the density of the crystal.
3)Schottky Defects:- If in a ionic crystal +ve or –ve ions missing their lattice sites so that electric neutrality is maintained
                 Ex: NaCl, KCl, CsCl, AgBr.
4)Frenkel Defect: - If an ion missing their lattice site (causing vacancy or hole their) and comes in the interstitial side, so maintain electric neutrality or Stoichiometry of the crystal is called Frenkel defect.
                 Ex: ZnS, AgCl, AgBr, AgI.

2)Impurity defect

3)Non stoichiometric defect

Classification of solids on the basis of electrical conductivity

semiconductors

Intrinsic semiconductors

Extrinsic semiconductors

Magnetic properties of solids:-

Diamagnetic substances :- Substances which are weakly repelled by external magnetic field is called as diamagnetic substances.

e.g:-Nacl

Paramagnetic substances :-

Substances which are attracted by external magnetic field is called para magnetic substances

Ferromagnetic substances :- substances which show permanent magnetism even in the absence of magnetic field is called feeomagnetci substances

Anti ferromagnetics substances :-

Substances which are expected to posses’ paramagnetism and ferromagnetism on the basis of magnetic moments of the domains but actually they posses Zero magnetic moment are called anti- ferromagnetic substances.

Ferrimagnetic substances :-
Substances which are expected to posses large magnetism on the basis of magnetic moments of the domains but actually have small net magnetic moment are called ferrimagnetic substances.

Atomic Number and Isotopes

Atomic Number(z) :-
It is equal to the number of proton in an nucleus of an atom or it is equal to number of electrons in an neutral atom.
For example : Hydrogen has one proton(₁¹H) so its atomic number is 1,similarly for others.


Isotope :-
Atoms having same atomic number and diferent atomic masses(different neutons in their nuclei) are called isotopes so in isotopes element remains same but its atomic mass is different

Mole and Avogadro Number

A mole is the quantity of anything that has .the same number of particles found in 12.000 grams of carbon-12.That number of particles is Avogadro's Number, which is roughly 6.02x10²³. A mole of carbon atoms is 6.02x10²³ carbon atoms.

1 mole of carbon 12 atoms(¹²C)= 12g=6.023x10²³

Atomic weight and Atomic Mass

Mass :-
in actually what the particle in itor actual amount of material contained in it or how hard is to accelerate it or decelerate it ,mass is independent of everything that is gravitational force etc and it remains constant everywhere .It is measure in kg generally but for atoms it is measured in amu(atomic mass unit) which is few grams.

the weight of 1 proton or 1 neutron is approximateley equal to 1 amu

carbon 12(C-12) is taken as benchmark and carbon 12 has mass 12 amu

Atomic weight :-

 weight is the total amount of gravitational force exerted by gravity in it.So even on earth we have difference in our weights due to difference in gravitational forces .For atoms atomic weight is also calculated in "amu" but it is weighted average across many isotopes like we can take example of carbon it has isotopes like carbon 12,carbon 13,carbon 14 and the weighted atomic weight comes out to be 12.011 amu of all these isotopes as carbon 12 is most abundant in earth

Structure Of Atoms|Atomic Structure

Atom:-

An Atom is smallest indivisible constituent of matter.It means an atom cannot be divided into sub parts .Atom have sizes around 100 picometres.Every atom has a nucleus where all its mass get concentrated i.e almost 99.9% mass of an atom present in nucleus ,nucleus conation proton and neutron and electron revolves around nucleus which is binded by electro magnetic force between proton and electron an neutron have no charge.

In the nucleus proton and neutron is binded by nuclear force which is greater then the repulsive electro magnetic force between two proton in the nucleus.An atom mostly consist of same number of electron and proton .

If in any case an atom has fewer number of electron or more number of electron then protons then it is called an ion as it contains either positive or negative charge.

The number of proton represents to which chemical element certain atom belongs.so by knowing number of protons in an atom we can decide which element it is.

The neutron decides number of isotopes and the electron shows the magnetic properties of that atom

Rutherford Experiment:
Rutherford gold foil experiment is a famous experiment in which he has fired alpha particles(helium nuclei) into a thin gold foil and observed below:-

Most of the particles pass through the foil without any deviation
Most pass with some deflection and some pass with heavy deflection like 90 degrees.

So he concluded that every atom consist of a central part in which all its mass is concentrated due to which such heavy deflection occured.

Thomson Model of an Atom:-

Thomson atomic model also know as plum pudding model raisin pudding watermelon model it was dicovered by Thomson in 1898.In this model thomson considered that an atom has spherical shape and in it postive charge is uniformly distributed and - ve charge embedded in such a manner to give electrostatic stability to the atom.The radius of atim is approzimateley 10^-10  
metre and mass is uniformly distributed in it.

Discharge Tube Experiment or cathode ray experiment:-

Cathode ray i.e electrons always travel from cathode towards anode and in the absense of any force which can be electric or magnetic field it travels in straight lines and in presence of these fields it shows behavious like negative particles which proves cathode rays are negativeley charged particles.
Their behaviour can be observed easily with the help of fluorescent or phosphorus sent material.In this experiment it is also bserved that cathode rays does not depend upon material of electrode and nature of gas present in dischrge tube so it is considered basic constituent particle electron which is negativeley charged.

Charge and mass of electron:-

R. A. Millikan has done oil drop experiment to determine charge of electron which came out to be -1.6× 10^-19 C  or -1.6022× 10^-19 C
Mass of electron = 9.1094 ´ 10^-31 kg

Electromagnetic Radiation:-

electromagnetic radiation refers to wave of electromagnetic field which is travelling in space and carrying electromagnetic radiant energy it includes radio waves, microwaves, infrared, (visible) light, ultraviolet, X-, and gamma radiation.

generally electromagnetic radiations are radiant energy which consist of continuous oscillation of electric and magnetic field ,they travel in the vacuum with the speed of light and their oscillation is perpendicular to each other and also perpendicular to the direction of wave propagation and energy

The position of electromagnetic waves at any time can be pointed in electromagnetic spectrum by its frequency or wavelength at any time.In general electromagnetic spectrum has increasing frequency and decreasing wavelength with distance.

Characterstics of wave:-

i. Wavelength : The distance between neighbouring
crests or troughs is known as wavelength. It is denoted by λ.

ii. Frequency: The number of times a wave passes through a given points per second is known as
 frequency. It is denoted by v.

iii. Amplitude: It is the maximum height of crest or depth of trough of a wave. It is denoted by A.

iv. Velocity: The distance travelled by a wave in one second is called its velocity. All electromagnetic radiations travel with same velocity. It is denoted by c.
 It is equal to  3×10^8 m/sec.  .

v. Wave number : It is reciprocal of wavelength. It is denoted by v ̅=1/λ.

Wavelength and frequency:-
c=v λ.

C= Velocity of light,v= frequency and λ= wavelength

Planck's Quantum Theory:-


Photoelectric Effect:-
According to Planck when an photon hits a metallic surface a part of its energy called binding energy used for the the ejection of electron and rest is given to the ejected  electron in the form of kinetic energy.

Showing it in equation:
E=Be+KE
Where, E= energy of incident photon
BE = binding energy
KE = kinetic energy of the ejected electron
Or hv = kinetic energy of the ejected electron

Bohr's Model:-

Bohr given the theory that an electron revolves around the nucleus of an atom in fixed circular orbit without losing any energy ,an electron loses energy or gains energy only when it goes to other energy levels .

The main success of bohr model was in explaining Rydberg formula for spectral emission of hydrogen atom

Heisenberg's Uncertainity Principle:-

It states that it is impossible to determine simultaneously, the  exact position and exact  momentum (or velocity)  of  an electron.The product of their uncertainties is always equal to or greater than h/4π.

Schrodinger's Equation:-

Schrodinger's Equation used in  describing quantum mechanical behavior and it  predicts analytically and precisely the probability of events or outcome.

Quantum Numbers :-

Their are four quantum numbers :-

1)Principal quantum number

2)Azimuthal quantum number

3)Magnetic quantum number


4)Electron spin 


Quantum number specifies the size,shape and orientation of an orbital ,three quantum numbers needed to specify an orbital and to specify an electron all four quantum numbers needed.

Nodal surfaces or Nodes :-

The region where this  probability density function reduces to zero is called nodal surfaces or simply nodes.

Sheilding effect or screening effect:-

The outer electron experiences less attraction of positive charge of nucleus due to inner electrons ,this effect is called screening effect it increase with increase in Azimuthal quantum numbers.

Aufbau Principle:-

In the ground state of atom the orbital are filled in order of their increaseing energies and the order is as follows:-

Below is the order in which orbitals are filled:-

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 4f, 5d, 6p, 7s..

Pauli Exclusion Principle :-

No two electron have the same set of four quantum numbers and only two electron may exist in the same orbital and they must have opposite spin

Hund's rule of maximum multiplicity :-

Pairing of electron will not take place in an orbital  until  the pairing subshell is singly occupied.

Electronic configuration of atoms:-

Arrangement of electrons in different  orbitals of an atom.It is represente in two ways given below:-

Orbital diagram:, Each orbital of the  subshell is represented by a box and the electron is represented by an arrow  (↑) a positive spin or an arrow (↓) a negative spin and s^ap^bd^c...etc notation.

Stability of completely filled and half filled subshells :-

Symmetrical distribution of electrons- .completely filled or half filled sub-shells have  symmetrical distribution of electrons in them and are more stable

Exchange energy-The two or more electrons with the same spin present in the  degenerate orbitals of a sub-shell can exchange their position and the  energy released due to this exchange is called exchange energy.The number of exchanges is maximum when the  subshell is either half filled or completely filled. As a result the exchange energy is maximum and so  is the stability.