Organic Chemistry – Some Basic Principles and Techniques

 BASIC PRINCIPLES AND TECHNIQUES IN ORGANIC CHEMISTRY

Organic chemistry is the chemistry of carbon compounds except oxides of carbon and metal carbonates. The term organic literally means derived from living organism. All organic compounds contain carbon as their essential constituent. Carbon atom has unique property to form bonds with other carbon atoms. This property of forming bonds with atoms of the same element is called catenation. 

Carbon form strong bonds with many others elements and especially with other carbon atoms to form chains and rings that gives rise to millions of organic compounds.

CLASSIFICATION OF ORGANIC COMPOUNDS

Organic compounds are broadly classified in two ways.

1] Based on carbon skeleton

Aliphatic compounds

These are the compounds in which carbon atoms are joined to form an open chain. Their structure may consist of straight chain or branched chain.

e.g. CH₃ – CH₂ – CH₂ – CH₃

Cyclic compounds

These are the compounds in which carbon atoms are joined to form one or more rings. They are further classified into two types.

a] Homocyclic or carbocyclic

In these compounds, the ring is made up of carbon atoms only. They are further divided into two types.

i) Alicyclic compounds

These compounds show some of the properties similar to those of aliphatic compounds. Carbon atoms are linked by single bonds only.

ii) Aromatic compounds

These are the compounds which contains at least one aromatic ring which resembles benzene in their chemical behavior.

b] Heterocyclic compounds

These compounds include one or more heteroatoms like O, N, S etc. in the ring of carbon atoms. They are also divided into two types.

i) Hetero – alicyclic compounds

Alicyclic compounds which contain at least one heteroatom in the ring are called hetero-alicyclic compounds.

ii) Hetero – aromatic compounds

Aromatic compounds which contain at least one heteroatom in the ring are called hetero – aromatic compounds.

2] Based on functional group

An atom or a group of atoms in the organic molecule which determines its characteristic chemical properties is called the functional group.

e.g.   – OH, - X, - CHO, - COOH, - NH₂, etc. are functional group. The chemistry of every organic molecule is determined by the functional group it contains.

Homologous series

A series of organic compounds each containing a characteristic functional group, and the successive members differ from each other in molecular formula by a –CH₂– (methylene) group is called homologous series.

 

 

PURIFICATION OF ORGANIC COMPOUNDS

The purification of organic compounds involves the following processes.

1. Crystallization

This is the most common method used to purify organic solids which dissolve in particular solvent. The purification is done on the basis of differences in solubility of a given organic compound and impurities.

 

2. Sublimation

It is a process which is used for solids which directly change into vapor state upon heating without passing the liquid state and vapors on cooling give back the solid Substance. Impure samples of naphthalene, anthracene, camphor, etc. are purified by this method.

 

3. Distillation

The process in which liquid is converted into its vapor phase at its boiling point and the vapors is then condensed back to liquid on cooling is known as distillation. This method is used if the organic liquid is stable at its boiling point and it contains non – volatile impurities.

 

4. Fractional distillation

The process of separating and purifying the components of a mixture of two or more miscible liquids having different boiling points is known as fractional distillation. The liquid which is more volatile distills out first leaving behind the less volatile liquid in the distillation flask.

 

5. Steam distillation

Liquids which are immiscible with water but are steam volatile are separated by this technique. Aniline, nitrobenzene, bromobenzene etc. can be steam distilled.

 

6. Fractional crystallization

The process of separating the components of a mixture of two or more solids, having different solubilities in the same solvent at the same temperature, by step – wise crystallization is known as fractional crystallization.

 

7. Differential extraction

The organic solvents like benzene, chloroform, petroleum ether etc. are immiscible with water such solvents are used to extract an organic compound present in aqueous solution by the method of differential extraction.

 

8. Chromatography

Chromatography is the technique used for the separation, isolation, purification and identification of constituents of a mixture. This technique depends on the distribution of the mixture between two phase, one stationary phase and other moving or mobile phase. Depending upon the principle involved, it is divided into two types.

 

a) Adsorption chromatography

It is based on the principle of differential adsorption. Different compound are adsorbed on adsorbent to different degrees. It also has two types i) column chromatography and ii) thin – layer chromatography (TLC).

 

b) Partition chromatography

This technique is based on continuous differential partitioning of components of a mixture between stationary and mobile phases.

 

 

Determination of empirical formula

The formula of a compound which gives the simple whole number ratio of the atoms of various elements present in one molecule of the compound is called its empirical formula. It involves following steps.

Step – I

The percentage composition of elements present in a given compound is determined by quantitative analysis.

Step – II

The percentage of each element is divided by the respective atomic mass. This is gives the atomic ratio of constituents atoms present in a given compound.

Step – III

The simplest ration is found by dividing all the atomic ratios by the smallest atomic ratio.

 

Molecular formula

The formula which gives the actual number of atoms of various elements present in one molecule of the compound is called its molecular formula. Molecular formula is determined from empirical formula as –

Molecular formula = n x empirical formula

Where n is whole integer given by-

N    =          Molecular mass/ Empirical formula mass

 

 

 

ISOMERISM

The compounds having same molecular formula and different structural formulae are called isomers of each other. This phenomenon is known as isomerism. It has two main types.

 

1. Stereoisomerism

The stereoisomers have the same structural formula but differ in the arrangement of atoms or groups in space.

 

 

2. Structural isomerism

The structural isomers differ from each other in the arrangement of the atoms or groups within the molecules.

It can be further divided as :

 

a) Chain or nuclear isomerism

It is the type of isomerism in which the isomers differ in the chain of carbon atoms. For example, C₄H₁₀ has two isomers.

b) Position isomerism

It is the type of isomerism in which the different isomers differ in the position of the functional group. For example, C₃H₇OH has two isomers.

c) Functional isomerism

It is the type of the isomerism in which isomers have different functional group. For example, C₂H₆O has two isomers :

d) Metamerism

It is the type of isomerism in which the isomers differ in the nature of alkyl group attached to the same functional group. For example, C₅H₁₀O has two isomers.

C₂H₅ – CO – C₂H₅    (Diethyl Ketone) and       CH₃ – CO – C₃H₇ (Methyl propyl Ketone)

 

FUNDAMENTAL CONCEPTS IN ORGANIC REACTION MECHNAISM

Electron displacements in covalent bonds

 

Inductive effect

When an organic molecule has a polar covalent bond in its structure polarity is induced in adjacent carbon – carbon single bond too. This is called inductive effect. The arrow head put in the center of the bond is used to represent the inductive effect. The direction of arrow head indicates the direction of permanent electron displacement. For example,

This effect decreases rapidly as the length of carbon chain increases. There are two types of inductive effect.

i) – I effect

Atoms or group of atoms which are highly electronegative or carry positive charge are electron – withdrawing groups and such groups are said to have – I effect.

e.g. – F, - Cl, -Br, - I , - NO₂, - CN, - COOH, - COOR, - SO₃H, etc.

 

ii) + I effect

Atoms or group of atoms which are electropositive or carry negative charge are donating groups and are said to have + I effect.

e.g. Metals like Na, K, Mg, Zn etc. and alkyl groups such as – CH₃, - CH₂CH₃, - CH(CH₃)₂, - C(CH₃)₃, - C(C₂H₅)_3, etc.

 

Electromeric effect

The complete transference of shared pair of electrons to one of the atom joined by a multiple bond in presence of an attacking reagent this is known as electromeric effect.

This is a temporary effect and takes place only in the presence of an attacking reagent. For example:

 

Resonance effect

The polarity developed within a molecule is due to the interaction of two ∏ - bonds or a ∏ - bonds with the lone pair of electrons present on the adjacent atom is called the resonance effect or mesomeric effect. It is a permanent effect and depending, upon the direction of transfer of electrons it is of two types.

 

i) +R effect

When the transfer of electron is away from an atom or substituent group attached to the conjugated system, it is termed as +R effect. For example +R effect in aniline.

 

 ii) – R effect

When the transfer of electron is towards the atom or substituent group attached to the conjugated system, it is termed as – R effect. For example – R  effect in nitrobenzene.

 

 

Hyper conjugation

The delocalization of electrons due to overlap between a P – orbital and sigma (σ) bond of C – H is called hyper conjugation or no bond resonance. Greater the number of alkyl groups attached to a positively charged carbon atom, greater is the hyper conjugation interaction and greater is the stability of cation. Thus the relative stability of cation decreases in the order.

(CH₃)₃C⁺ > (CH₃)₂CH⁺ > CH₃CH₂⁺ > CH₃⁺

 

 

Bond fission

In any chemical reaction, when a reactant is converted into products one or more bonds in the reactant are broken and new bonds are formed. The process of breaking or cleavage of covalent bond is known as bond fission. The bond fission takes place in two ways.

 

i) Hemolytic fission

The symmetrical breaking of a covalent bond between two atoms such that each atom acquires one electron of the shared pair is called hemolytic fission or homolysis.

Such fission takes place in the presence of ultraviolet light or high temperature. The cleavage of a bond results in the formation of free radicals. A free radical is a neutral species (atom or group) which contain an unpaired electron. A hemolytic fission is represented as:

ii) Heterolytic fission

The unsymmetrical breaking of a covalent bond between two atoms such that the more electronegative atom acquires both the electrons of the shared pairs is called heterolytic fission or heterolysis .

Such a fission takes place in the presence of polar solvent. The cleavage of a bond results in the formation of ions. This ions formed are unstable and reactive. One of the ion has a positive charge called as cation and the other ion has at least one lone pair and a negative charge called as an anion. Organic reactions which proceed by heterolysis are called ionic or  heteropolar simply polar reaction. A heterolytic fission is represented as:

The species in which carbon atom passes a positive charge is called carbanion and the species in which carbon atom possesses negative charge is called carbanion.

Example of heterolysis is,

Reaction intermediates

 

i) Free radicals

An uncharged species which is electrically neutral and contains a single electron is called free radical.

Free radical is highly reactive and therefore has a transitory existence i.e. it is short – lived. The stability of free radicals decreases in the order triphenyl methyl > benzyl > allyl > 3ᵒ > 2ᵒ > 1ᵒ > methyl > vinyl.

 

ii) Carbocation

A species in which carbon atom bears a positive charge is called a carbocation. Positively charged carbon is sp² hybridized. It is electron – deficient. It is Lewis acid and act as an electrophile. It has planer geometry.

e.g. tetra – butyl carbocation (CH₃)₃C⁺.

 

iii) Carbanion

A species in which carbon atom bears a negative charge is called a carbanion. Negatively charged carbon is Sp³ / Sp² hybridized. It is electron – rich. It is Lewis base and act as a nucleophile. It has pyramidal geometry.

e.g. methyl carbanion      CH₃.

 

iv) Carbenes

The highly reactive intermediate containing neutral and divalent carbon atoms is called carbene.

For example, CH₂

 

 

Types of attacking reagent.

1) Electrophiles

Electrophiles are electron – deficient species. They are either positively charge species like H⁺, NO⁺₂ etc. or molecules having incomplete octet of electrons like BF₃, AlCl₃, ZnCl₂ etc.

Since electrophiles are electron deficient they accept a pair of electrons from donor atoms and thus they are electron loving reagents. All electrophiles are basically lewis acids.

 

2) Nucleophiles

Nucleophiles are electron rich species. They are either negatively charged species like OH^-, CN^-, Cl^-, Br^-etc. or molecules containing at least one lone pair of electrons on central atom like H₂O, NH₃, H₂S, R-OH, R-NH_2, etc. since nucleophiles are electron rich, they donates pair of electrons to acceptor atoms and thus they are nucleus loving reagents. All nucleophiles are Lewis base.

 

 

 

Types of organic reactions

1) Substitution reaction

A reaction in which an attacking species replaces another atom or group in substrate is called substitution reaction.

e.g.

2) Addition reaction

When two molecules combine to form one product molecule, it is called an addition reaction.

e.g.

CH₂ = CH₂ (Ethylene)   +     HCl    →    CH₃ – CH₂ – Cl (Ethyl chloride)

  

3) Elimination reaction

When one molecule is split into two fragment molecules, it is called an elimination reaction.

e.g.

4) Rearrangement reaction

A reaction in which either the carbon skeleton or the functional group or both are modified is known as rearrangement reaction.

e.g.

Smartphone Chemistry

Chemistry of Smartphone

About 20 years before no one use smartphones but nowadays everyone have a smartphone. Apple iPhone 13 Pro, Google Pixel 6 Pro, Oppo Find X3 Pro, OnePlus 9 Pro, Sony Xperia 1 III, Asus ROG Phone 5s Pro and Xiaomi 11T Pro are examples of some popular smartphones. This article is all about chemistry behind smartphones by Chemistry Notes Info.

Different Chemistry Elements in Smartphones

Typically smartphone contains many elements like Silver, Gold, Lithium, Praseodymium, Terbium, Yttrium, Gadolinium, Indium, Tin, Oxygen, Carbon, Copper, Tantalum, Silicon, Oxygen, Antimony, Arsenic, Phosphorus and Gallium.

Generally On Average a Smartphone Contains About 

• 300 mg Silver (Ag having Atomic No. 47, Atomic Mass 107.87)
• 30 mg Gold (Au having Atomic No. 79, Atomic Mass 196.97)

Battery- Generally smartphones have Li-Ion Battery, this battery have Lithium Cobalt Oxide as a +ve electrode and Carbon or Graphite as a -ve electrode. This -ve electrode release electrons which travel towards +ve electrode as a result provide power to your phone.

Screen- Screen contains following elements which provide color to screen to display visual content.

•  Praseodymium (Pr having Atomic No. 59, Atomic Mass 140.91)
• Terbium (Tb having Atomic No. 65, Atomic Mass 158.93)
• Yttrium (Y having Atomic No. 39, Atomic Mass 88.91)
• Gadolinium (Gd having Atomic No. 64, Atomic Mass 157.25)

 Touch- Touchscreen takes inputs from user and are transparent, all these are possible due to following elements

• Indium (In having Atomic No. 49, Atomic Mass 114.82)
• Tin (Sn having Atomic No. 50, Atomic Mass 118.71)
• Oxygen (O having Atomic No. 8, Atomic Mass 16)

Wiring- Wiring or electrical circuits are made up of copper and capacitors are made up of Tantalum. Capacitor store regulate electricity and loose electrical charge in fraction of seconds.

• Copper (Cu having Atomic No. 29, Atomic Mass 63.55)
• Tantalum (Ta having Atomic No. 73, Atomic Mass 180.95)

Microchip- Microchip or CPU (Central Processing Unit) also called brain of smartphone is made-up of silicon, oxygen, antimony, arsenic, phosphorus and gallium. All these elements are used to produce highly conductive powerful microchips so you can play games, watch videos, click photos, use your phone camera for taking selfy, audio video recording, calling, chatting, using apps like whats app, facebook, twitter or whatsoever stuff you like to do with your smartphone is possible due to chemistry.

• Silicon (Si having Atomic No. 14, Atomic Mass 28.09)
• Oxygen (O having Atomic No. 8, Atomic Mass 16)
• Antimony (Sb having Atomic No. 51, Atomic Mass 121.76)
• Arsenic (As having Atomic No. 33, Atomic Mass 74.92)
• Phosphorus (P having Atomic No. 15, Atomic Mass 30.97)
• Gallium (Ga having Atomic No. 31, Atomic Mass 69.73)

What's Inside Your Smartphone

Smartphone is made-up of different components which are assembled to make smartphones. Like display (to show visual content), touchscreen (to take inputs from user), cameras (to take photos, selfy and to shoot videos). Microphone (to receive audio or to record sound), case (body of phone), battery (to provide power), sim card slot (for sim), speakers (for sound, to listen music), sensors (for different purpose like ambient light sensor for light intensity means automatically set screen brightness according to surrounding light and ultimately save battery life. 

Gyroscope and accelerometer to play video-games as these sensor tracks phone movement, digital compass to detect north direction for maps and navigation, proximity sensor used to prevent unwanted touch commands by locking phone during phone call when you bring phone near your ear). 

Motherboard (printed circuit board containing principal components of smartphone with connectors for other circuit boards to be slotted into), memory (to store data, movies, photos, videos, songs), transceiver (to transmit and receive communications), radio (to transmit data and to receive data).

Cell phone radio (that communicate with cell tower, when you make call) wifi radio (to download big files, movies songs etc and they consume less battery as they travel very less distance) bluetooth radio, NFS rado, GPS radio etc. All these components contain some chemical elements of periodic table and when all components are assembled they give you smartphone which you use daily.

CHEMISTRY GK

INNOVATIVE EDUCATION

11 Class Chapter 2- Structure of Atom

Structure of Atom Class 11 Chemistry Notes Chapter 2

Atomic  Theory of matter :-

                                            According to this theory, atom is the ultimate particle of matter. This atomic theory of matter is also known as Dalton’s  Atomic theory (1808).

Cathode ray discharge tube experiments: - 

• Cathode rays start from cathode and move toward anode.
• These rays are not visible but there behavior can be observed with fluorescent or phosphorescent material.
• In the absence of magnetic or electric field these rays travels in straight lines. 
• In the presence of magnetic or electric field, the behavior of cathode rays is similar to Negatively  charged  particles. Which suggest that these rays contain negatively charge particles called electron.
• Cathode rays (or electrons) do not depend on the material of the electrode and nature of the gas in the tube so electrons are basic constituent of all atoms.

Charge (e) to mass (me) ratio of electron 

• Measured by  J. J. Thomson (1897).
• By using cathode ray tube.
• By applying electrical & magnetic field perpendicular to each other & also perpendicular to path of electrons.
• He proposed  deviation of particles from their path in presence of magnetic or electrical field depend upon the following-

1.     Magnitude of  – ve  charge on particle

i.e. if magnitude of charge on particles is greater than interaction with magnetic or electric field is greater so deflection is also grater.

2.     Mass of particles

i.e. particle is lighter then deflection is greater.

                 3.  Strength of magnetic or electric field.

i.e. if strength of magnetic field or voltage, at electron is increases then deflection of e^-  also increases.

        =>  value of e/m_e = 1.758820× 10¹¹ C kg^-1

Charge of electron

=  Determine by  R. A. Millikan

=  By oil drop experiment (1906-1914)

=  Charge on e^- =  -1.6× 10^-19 C

= Present accepted value , e^- = -1.6022× 10^-19 C

Mass of electron

 From charge on e^- & e/m_e

 We get,                 

             M_e = 9.1094 ´ 10^-31 kg

Discovery of protons

=  Discovered by E. Goldstein.

=  In modified cathode ray tube gives +ve charge carrying particles known as canal rays.

=  Lithest & smallest +ve ion obtained from Hydrogen called proton.

Characteristics

1)    Depend upon, nature of gas present in cathode ray tube.

2)    Charge to mass ratio of particles depends on gas from which these originate.

3)    Some of +ve charged particles carry a multiple unit of electrical charge.

4)    Behavior of protons in magnetic or electric field is opposite to that of electron behavior.

Discovery of neutrons

  Discovered by Chadwick (1932).

  By bombarding a thin sheet of beryllium by alpha particles.

  Electrically neutral particles were emitted known as neutrons.

Thomson model of atom

  Given by J.J Thomson (1898)

  According to J.J. Thomson, atoms posses a spherical shape, 

with radius about 10^-10 m, in which + ve charge is uniformly distributed.

  Electrons are embedded in such a manner to give most stable electrostatic arrangement.

  Other names of this model plum pudding, raisin pudding, watermelon model.

  Mass is assumed to be uniformly distributed in atom.

Rutherford’s nuclear model of atom

=  Given by Rutherford & his students Ernest Marsden and Hans Geiger.

=  By α- particles scattering experiment-

Rutherford’s nuclear model of atom

=  When beam of high energy α- particles was directed at gold foil, then tiny flash of light observed at photographic plate.

          Rutherford observed that-

• 1)    Most of the α-  practical  passed  through gold foil un-deflected.
• 2)    A small fraction of α- particles was deflected by small angles.
• 3)    A very few α- particles (about 1 in 20,000) bounced back means deflected by nearly 180⁰

                  From above observations he concludes the structure of atom.

1)    Most of space in atom is empty because most of α- particles passed un-deflected.

2)    Few +ve charged α- particles were deflected.

Because + ve charge of the atom present in center in very small volume that repelled & deflected the +ve charged α- particles.

3)    Volume of nucleus is negligible as compared to total volume of atom

i.e.  radius of atom = 10^-10m  (approx)

radius of nucleus =  10^-15m  (approx)

       On the basis of observation & conclusion Rutherford proposed model of atom as-

1)    +ve charge & most of mass present in the center of atom known as nucleus.

2)    Electrons moves around nucleus with very high speed in circular paths known as orbits.

3)    Electrons and nucleus (protons) are held together by electrostatic force of attraction .

Atomic number (Z) = no of protons in the nucleus of an atom

                                       = no of electrons in a neutral atom

Mass number (A) = number of protons (z) + number of Neutron (n)

Isobars :- 

              These are atoms with same mass number but different atomic number.

             

Isotopes: - 

               These are atoms with same atomic number but different atomic mass no.

            

Wave nature of electromagnetic radiations: -

First explanation given by James Maxwell (1870).

1)    Oscillating magnetic & electric fields produced by the oscillating charged particles are perpendicular to each other and also perpendicular to the wave direction of propagation.

2)    These waves do not require medium i.e. electromagnetic wave can travel in vacuum.

3)    Electromagnetic radiation differs from one another in frequency or wavelength gives electromagnetic spectrum.

4)    Different units are used to represent electromagnetic radiation.

                                 n = frequency, 

                                l = wavelength.

Particle nature of electromagnetic radiation :-   

                                                                        Also known as Planck’s  Quantum theory

= Planck suggested that the atoms and molecules can absorb or emit energy in discrete quantities not in continuous manner. Planck gives it name as quantum. Energy (E) of  quantum of  radiation is directly proportional to its frequency(n)

 i.e.            E=hn

Where,      h = planks constant = 6.626× 10^-34 js

                                                     

Photo electric effect:-

=  given by H. Hertz (1887)

=  When a beam of light strike a metal surface then electrons were ejected. This phenomena is known as photo electric effect.

1.     Electrons ejected from metal surface, when beam of  light strike the metal surface.

2.     Number of electron ejected is directly proportional to intensity (or brightness) of light.

3.     There is characteristic minimum frequency (n₀ threshold frequency) below which photoelectric effect is not observed.

4.     If n > n₀ then electrons comes out with kinetic energy which increases with increase in frequency of light.

Kinetic energy of ejected electrons is given by-

h n = h n₀+ ½(m_eV²)

Spectroscopy:- 

                      study of  absorption or emission spectra is called spectroscopy .

Bohr’s model for hydrogen atom:-

=  Explain by Nails Bohr (1913).

=  Postulates for Bohr’s modal are,

    1.     Electron in hydrogen atom move around nucleus in circular path of fixed radius and energy. these paths are called orbits.

    2.     Energy of electron does not change with time.

However, when electron move from lower to higher stationary state. It absorbed some amount of energy and energy release when it comes back.

    3.     Frequency of radiations emitted or absorbed when transition of electron occur is given by

Where, E1 & E2 is lower & higher energy state.

     4.     Angular momentum of n electron in given stationary state is given by-

[Where n =1,2,3.....]

Limitation of Bohr’s model:-

1.     Bohr model fail to explain fine detail of hydrogen atom spectrum observed by spectroscopic, techniques.

2.     It fails to explain spectrum of other atom except hydrogen atom.

3.     It fails to explain splitting of the spectral lines in presence of electric field (stark effect) or magnetic field ( Zeeman effect ).

4.     Fail to explain formation of molecules from atoms by chemical bonding.

Dual behaviour of matter :-

=  Explain by de-Broglie (1924)

=  He explain that matter also behave like radiation and exhibit dual behavior means both like particle and wave like properties .

= Relation

   Where  l =  wavelength.

             m = mass of particle ,

             v = velocity of particle,

              p = momentum

Heisenberg’s uncertainty principle:-

 Given by Werner Heisenberg (1927)

He explain that it is impossible to determine simultaneously the exact position and exact momentum (or velocity) of an electron.

Mathematical explanation

                                     

     Where,  Dx= uncertainty  in position

                   

                   DV_x  = uncertainty in velocity or momentum

Quantum mechanical model of atom:-

• Branches of science which explain duel behavior of Metter is called quantum mechanics. 
• Quantum mechanics independently developed by Werner Heisenberg and Erwin Schrodinger (1926).
• Fundamental equation developed by Schrodinger. (He won Nobel Prize in 1933).
• Equation for a system (atom or molecules was, energy does not change with time)

Principle quantum number ‘n’ :-

·        It is a positive Integer with value of n = 1,2,3......

·        It determine size and energy of orbital.

·        It also identifies the shell with increase in number of allowed orbital. 

And given by n²

N      =1,    2,    3,    4........

Shell = k,    l,    m,    l......

·        Size of orbital increase with increase in n.

             Azimuthal quantum no.‘l’  :-

·        It is also known as orbital angular momentum or subsidiary quantum no.

·        It defined 3D shape of orbital.

·        For given value of n possible value of  

        L= 0,1,2,3,4,5,----------(n-1) ,

                    Ex :- if   n=1   then   l=0

                             if   n=2   then   l=0,1

                             if   n=5   then   l=0,2,3,4

·        Each shell consists of one or more sub-shells.

·        No of sub-shells = value of  n

If  n= 1  then  1 sub-shell =  (l=0)

If  n= 2  then  2 sub-shell =  (l=0,1)

If  n= 3  then  3 sub-shell =  (l=0,1,2)

·                      Value of    l =  0,  1,  2,  3,  4,  5  ----------

     Notation for sub-shell= s, p, d,   f,   g, h--------------

·        Sub-shell notation

n	l	Sub-shell   notation
1	0	1s
2	0	2s
2	1	2p
3	0	3s
3	1	3p
3	2	3d
4	0	4s
4	1	4p
4	2	4d
4	3	4f

 Magnetic orbital quantum no ‘m_i’ :-   

·        This quantum no (m_i) gives information about orientation of  the  orbital .

·        m_i = (2l+1) i.e. if value of   l  is  1 then value of  m_i = 2×1+1=3=(-1,0,1)

Value of p	0	1	2	3	4	5
Sub-shell notation	S	P	D	F	G	H
No of orbital’s	1	3	5	7	9	11

Electron spin quantum (m_s)  :- 

·        Proposed by G. Uhlen Beck & S. Goodsmit (1925).

·        Electrons spins around its own axis.

·        M_s have two value +1/2 & -1/2.

·        M_s gives information about orientation of the spin of the electron.

Aufbau principle   :- 

                              According to this principle, in the ground state of the atoms the orbital’s are filled in order of their increasing energies. Means electrons enter higher energy orbital’s,  so order in which orbital’s are filled is 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p.

Pauli exclusion principle  :-

·         Given by W. Pauli (1926).

·        Two electrons in an atoms can’t have same set of 4-quantum no.

·        Only two electrons may exist in same orbital and these electrons must have opposite spin.

Hund’s  rule of maximum multiplicity :-.

·        According to this rule, pairing of  electron in the orbital’s belonging to the same sub-shell (p, d or f) does not take place until each orbital belonging to that sub-shell has got one electron each i.e. it is singly occupied.

Structure of Atom Class 11 MCQ

1. Who discovered anode rays :

 Goldstein
 Rutherford
 J. Stanley
 J. J. Thomson

2. Neutron was discovered by :

 Rutherford
 Chadwick
 Austin

 Langmuir

3. Radioactive isotope of hydrogen has ________ number of neutrons :

 0

 1

 2

 3

4. Cathode rays are deflected by :

 A magnetic field only
 An electric field only

 By Both
 By None

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