Chemistry Podcast

Saturday, 25 June 2016

What is Hyperconjugation

Definition of Hyper conjugation

What is Hyperconjugation
What is Hyperconjugation?
Hyperconjugation is stabilizing interactions that are results from interaction of electrons in a sigma (σ-bond) (usually C-H or C-C) with an adjacent empty or partially-filled p-orbital or a pi (π) orbital to give an extended molecular orbitals that increases stability of system.
Hyper-conjugation is chemistry terminology and also known as Sigma (σ) electron delocalization.
Also,
        The movement of pi (π) electrons through p-orbital pathway is the Mesomeric-effect and leads to the resonance.
        The movement of sigma (σ) electrons through adjacent pi (π) system or a carbocation is the hyperconjugation. And hyper-conjugation therefore involves the sigma (σ) electron delocalization.
definition of hyper conjugation
The electrons of sigma (σ) bond between C and H are involved in the delocalization.
In the upper structure there is no bond between C and H due to the migration of sigma (σ) bond. Hence hyperconjugation is also known as “no bond resonance”.
But,
       This does not mean that the H-atom is completely detached from structure.  As it indicates the some degree of ionic character in C-H bond and some single bond character between C-C double bond.

When we see Toluene structure, there is a partial negative-charge on the C-atom bonded to the methyl (-CH3) group and the methyl C-atom is slightly positive-charge. This is due to hyperconjugation and has proved by the X-Ray diffraction studies.
Toluene is an example of "heterovalent hyperconjugation" or "sacrificial hyperconjugation", because the contributing structure (of toluene in hyperconjugation) contains one two-electron bond less than normal Lewis formula for the toluene.
"heterovalent hyperconjugation" or "sacrificial hyperconjugation"
Hyperconjugation can account for the (I-effect) Inductive effect. In Toluene, methyl group exhibits the +I effect that is responsible for the polarization of the electron (e-) density.

The interaction between filled pi (π) or p-orbitals and adjacent antibonding sigma (σ *) orbitals gives "negative hyperconjugation", example of negative hyperconjugation is fluoroethyl anion.
The interaction between sigma (σ) bonds and an unfilled or partially filled pi (π) or p-orbital gives "isovalent hyperconjugation", example of isovalent hyperconjugation is tert-butyl cation.

What are the requirements for the Hyper-Conjugation?

Requirements for the Hyper-Conjugation is described below-
  • Hyper-Conjugation exists in the carbocations, free radicals and alkenes and arenes.
  • The alpha (α) C-atom next to the pi (π) bond (double bond) or C free radical or C+ (carbocation) should be sp3 hybridized with at least one H-atom bonded to it.
Hyper-Conjugation exists in the carbocations, free radicals and alkenes and arenes

What is the effect of hyperconjugation on chemical structure?

  • Due to hyperconjugation C-C single bond gains some double bond character while C=C double bond gains some single bond character.
  • Therefore C=C double bond length in the substituted alkenes at all times greater than in ehtene.

Based on the valence-bond-model of the bonding, hyper-conjugation can be described as the "double bond- no bond resonance" but really it is not what we would say "normally" resonance.

What is main difference between resonance and hyperconjugation?

Resonance involves pi orbitals but Hyperconjugation involves a sigma orbital, usually a C-H or C-C bond.

Sunday, 1 May 2016

what is coagulation

COAGULATION

Coagulation: - The process of setting of colloidal particles is called coagulation or precipitation of the sol.
The coagulation of the lyophobic sols can be carried out in the following ways:-
1.      By electrophoresis: - The colloidal particles move towards oppositely changed electrodes get discharged and precipitate.
2.      By mixing two oppositely charged sols: - Oppositely charged sols when mixed almost equal proportional neutralise then changed and get partially or completely precipitated.
3.      By Boiling: - When a sol is boiled the adsorbed layer is disturbed due to increased collisions with the molecules of the dispersion medium. This reduces the charge on the particles and ultimately led to setting down in the form of a precipitate.
4.      By Persistent dialysis: - On prolonged dialysis, traces of the electrolyte present in the sol are removed almost completely collides become unstable and ultimately coagulate.
5.      By addition of electrolyte : -  When excess of electrolyte is added the colloidal particles precipitated, the reason is that colloids interact with ions carrying change opposite to that present on themselves, this causes neutralisation leading to their coagulation. 
Coagulation of Lyophilic Sols: - There are two factors which are responsible for stability or the lyophilic sols. These factors are change and salvation of the colloidal particles. When these two factors are removed, a lyophilic sol can be coagulated. This is done,
(i)     By addition of an electrolyte
(ii)   By adding a suitable solvent
Protection of Colloids:-
Lyophilic sols are more stable than lyophobic sols. Lyophilic colloids have a unique property of protecting lyophobic colloids. When a lyophilic sol is added to lyophobic sol, the lyophilic particles (colloids) covering up the particles of lyophobic sol.
Emulsions:-
An emulsion is a colloidal dispersion in which both the dispersion medium and dispersed phase are liquids generally; one of the two liquids is water. There are two types of emulsions.
1.      Oil dispersed in water (o/w type) and
2.      Water dispersed in oil (w/o type)
1.      O/W type – water act as a dispersion medium.
                                 Example: - Milk and vanishing cream.
2.      W/O type - oil act as dispersion medium.
                  Example: - Butter and cream.
Colloids Around Us: - Most of the substances all we come across in our daily life are colloids, for example meals, clothes, wooden, furniture, houses, newspaper are largely composed of colloids.
Application of Colloids: - Colloids are widely used in the industry.
Example:-
·         Electro Precipitation of Smoke: - The smoke, before is comes out from the chimney, is led through a chamber containing plates having a charged opposite to that carried by smoke particles. The particles on coming in contact with these plates lose their charge get precipitated, the particles thus settle down on the floor of the chamber. The precipitator is called Cottrell precipitator.
Coagulation - Electro-Precipitation of Smoke at Power Station
Electroprecipitation at Power Station
·         Purification of Drinking Water: - Alum is added to water (that contain impurities) to coagulate the suspended impurities make water fit for colloidal in nature.
Example: - Argyrol is silver sol is used as an eye lotion.
·         Medicines :- Most of the medicines are colloidal in nature Ex:- Argirol is a silver sol used as an eye lotion.
·         Tanning  :- When a hide (Animal skin) , which has +ve  charged particles is soaked in tanning (or chromium salt) which contains – ve  charged particles , mutually coagulation take place. This result in the hardening of leather. This process is termed as tanning.
·         Photographic Plates and Films: - Photographic plates and films are prepared by coating an emulsion of the light sensitive silver bromide in gelatin over glass plates or celluloid films.
·         Rubber Industry: - Latex is a colloidal solution of rubber particles which are negative charged Rubber is obtained by coagulation of latex.
·         Industrial Products: - Paints inks, synthetic plastics, rubber, cement, graphite lubricants, etc. are all colloids solution.
      Coagulation in Chemistry:- In Chemical Science, coagulation is the process of setting of colloidal particles is called coagulation or precipitation of the sol. 
coagulation in chemistry
Coagulation Process Diagram

      Coagulation in Biology:- In Biological Science, coagulation is also called as clotting, means blood in body changes from liquid state to gel like state which further changes into blood clot.
      Daily Life Example Of Coagulation:- Curd (Dairy Product form by coagulating milk), Water Treatment (Coagulant is pour in water to destabilize the colloidal suspensions or impurities to take place coagulation).

Tuesday, 26 April 2016

What is an Element

What is Element ?

Definition of Element

          Substance which consists of only one type of atom is known as element.
So we can say that, an element is a substance which is made up entirely from the one type of atom.

Example of Element

what is element in science
Element Hydrogen, Element Carbon, Element Oxygen, Element Nitrogen, Element Chlorine, Element Iron, Element Copper, Element Gold, Element Silver, etc.
Element Carbon is made from atoms containing six protons, six neutrons and six electrons. Symbol of element carbon is ‘C’. Atomic Number of element carbon is 6. Atomic Mass of element carbon is 12.0107 amu. Melting Point of element carbon is 3500.0 °C (3773.15 K, 6332.0 °F). Boiling Point of element carbon is 4827.0 °C (5100.15 K, 8720.6 °F). Element Carbon is classified as Non-metal. Crystal Structure of element carbon is Hexagonal. Density @ 293 K of element carbon is 2.62 g/cm3. Color of element carbon is generally black.
If you wish to change the number of protons in an atom than ultimately you change the type of element.
Elements are the substance that consists of only one type of atom.
Molecule has two different atoms.
Elements contains one or more of same type of atom.

Elements Example-

  1. Element Hydrogen – 1 proton per atom
  2. Element Carbon     – 6 protons per atom
  3. Element Oxygen    – 8 protons per atom
  4. Element Copper     – 29 protons per atom
  5. Element Gold         – 79 protons per atom

Labeling of Element in Periodic Table

2      -     Proton Number- it shows what element it is. (Atomic Number)
He   -     Name of the Element
4     -      Total Atomic Weight- Number of Protons + Number of Neutrons.
by Chemistry Notes Info @ www.chemistryNOTESinfo.com

Sunday, 24 April 2016

What is an atom?

What is an atom?

Atom is basic building block of all matter.

An Atom Have

1. Nucleus

  • Nucleus is very small and heavy part of the atom.

2. An Surrounding Electron Cloud

  • Surrounding electron cloud is large and lightweight part of the atom.

Nucleus of an Atom

 Nucleus Contains

Protons

  •  Protons have a positive charge.
  •  All atoms are distinguished by the number of protons it has (atomic number).

Neutrons

  •  Neutrons have no charge.
  •  Neutrons have same mass as protons.

Electron Cloud of an Atom

 An Electron Cloud of an Atom Contains

Electrons

  • Electron have a negative charge.
  • Electrons are contained within the shells of electron cloud.
  • Electrons have very small mass as compared to neutrons and protons.
  • Electron move in orbital motion around nucleus.
  • Electrons decides how bonds formed.

Atomic Structure

Structure of atom
What is Atom - Atomic Structure
I think now you have lot of information about

What is Atom ?

Matter found around us in nature (like iron rod, glass, cup, pen, pencil etc.) is made up from very small particles, which is known as atoms.
we also says that "atoms are very small particles which made matter" so atom is fundamental unit of matter.
Greek Philosopher, Democritus describe atom as very small indivisible particle.
'New System of Chemical Philosophy' is a book about atom written by John Dalton in 1703.
 by Chemistry Notes Info @ www.chemistryNOTESinfo.com

 

Saturday, 16 April 2016

10 Class- Periodic Classification of Elements

Periodic Classification of Elements

In year of 1800 about 30 elements were known but at present we know about 114 elements. All these elements have different properties. So to study about these elements easily, scientists start searching some patterns in the properties to arrange these elements.

Early Attempts in the Classification of Elements

                                                                   This is practice to arrange elements in order out of chaos, means arranging elements in group of metals and non-metals. Chaos means complete disorder or confusing. Furthermore attempts were made to achieve best classification of the elements.

Dobereiner’s Triads

                             A German chemist, Johann Wolfgang Dobereiner in 1817 tried to arrange elements in the group of 3-elements in each group with similar properties and he called these groups as ‘Triads’. Dobereiner shows that when we take any triad and arrange its elements in the order of increasing atomic masses then the atomic mass of the middle element in the triad is roughly equal to the average of the 1st and 3rd element of the triad.

Dobereiner Triads

Li
Na
K
Ca
Sr
Ba
Cl
Br
I
In first triad Li, Na, K atomic mass of   Na (23) = [ Li(7) + K(39)]/2

Newlands Law of Octaves

                                      An English scientist, John Newlands in 1866 arranges known elements in order of their increasing atomic masses. At that time he started with Hydrogen as 1st element with lowest atomic mass and ended at Thorium as 56th element.  John Newlands observe that the property of every eighth element  is similar to that of first element and compare this to octaves of music so he called it ‘Law of Octaves’ and this is known as ‘Newlands Law of Octaves’.

Newlands Octaves

H
Li
Be
B
C
N
O
F
Na
Mg
Al
Si
P
S
Cl
K
Ca
Cr
Ti
Mn
Fe
Co and Ni
Cu
Zn
Y
In
As
Se
Br
Rb
Sr
Ce and La
Zr
-
-

1.     Newlands law of octaves is applicable only up to Calcium and after Calcium it is not applicable because after Calcium every eighth element is do not similar to that of first element. 
2.     Newlands assumed only 56 elements exists in nature but later several elements discovered whose properties are very different to get fit in Newlands law of octaves. 
3.     With the discovery of new elements, Newlands try to fit these elements in octaves so he put two elements in same slot and Newland also put elements with different properties in same slot for example Co and Ni placed in F, Cl column.

Mendeleev’s Periodic Table

                                      A Russian chemist, Dmitri Ivonovich Mendeleev in 1872 published his ‘Mendeleev Periodic Table’ in a German journal.  He arranges elements in the form of table on the basis of fundamental property of elements i.e. atomic mass and also on the basis of similarity of chemical properties of elements, means elements with similar chemical properties are placed together in table.

Mendeleev Periodic Law

                             According to this law “the properties of elements are the periodic function of their atomic masses”.
In Mendeleev periodic table horizontal rows are called as ‘Periods’ and vertical columns are called as ‘Groups’.

Mendeléev’s Periodic Table

10th Class- Mendeleev periodic table, Periodic Classification of Elements Xth Class Chemistry Notes Part-1

Achievements of Mendeléev’s Periodic Table

                                                          Mendeléev’s Periodic Table contains some gaps but Mendeléev predicted that these gaps are filled by elements discovered in future. And named these undiscovered elements by placing eka (one) as a prefix to the name of preceding element of the same group. For example Gallium discovered later but Mandeleev predict it as Eka-Aluminium.
Properties of Eka-Aluminium and Gallium
Property
Eka-Aluminium
Gallium
Atomic Mass
65
69.7
Formula of Oxide
E2O3
Ga2O3
Formula of Chloride
ECl3
GaCl3
This prediction of Mandeleev proves correctness and usefulness of Mendeléev’s Periodic Table. Another achievement of Mandeleev is that many scientists now recognize him as originator of the concept on which periodic table is based and also when inert gases (means Nobel gases like He, Ne, Ar) are discovered, they are placed in separate column without disturbing existing order of elements.

Limitation of Mandeleev Classification

                                                These given below are the limitation of Mandeleev Classification. 
1. Position of Hydrogen- No fixed position given to Hydrogen as it behaves like both alkali metals and halogens. Like alkali, Hydrogen react with halogen oxygen and sulphur and also like halogen, Hydrogen exist in diatomic form and react with metals and non-metals. 
2. Isotopes- Isotopes have similar chemical properties but different atomic masses, so Isotopes are challenge to Mandeleev Periodic Law. 
3. Prediction of New Elements- Atomic masses of elements do not increase in regular manner so we cannot predict how many elements can be discovered between two elements.
Modern Periodic Table

                             Henry Moseley in 1913, after performing many experiments proves that atomic number is more fundamental property than atomic mass of an element. So he prepare periodic table on the basis of atomic number means elements are arranged in the order of increasing atomic number in Modern Periodic Table.

Modern Periodic Law

                             According to this law “the properties of elements are the periodic function of their atomic number”.
In Modern Periodic Table limitation of Mandeleev Classification are removed. 

Modern Periodic Table

moseley modern periodic table


Position of Elements in Modern Periodic Table

                                                          Modern Periodic Table contains 18 vertical columns (means 18 Groups) and 7 horizontal rows (means 7 Periods).
In Group- Elements in a group have same number of valence electrons means identical outershell electronic configuration, but as we move downside in a group number of shells increases.
In Period- Elements in a period have same number of shells. Also as we move from left to right in a period, atomic number increases by one unit so number of valence shell electrons also increases by one unit.

Trends in the Modern Periodic Table

Valency

          Number of valence electrons in outer most shell of any atom is called valency of that atom. As we move from left to right in a period, atomic number increases by one unit so valence electrons also increases by one unit but in a group it remains constant.

Atomic Size

                   Atomic size is determined by atomic radius.
In a Period- Atomic radius decreases as we move from left to right in a period, because as we move from left to right in a period Nuclear Charge (+ve) increases which pulls electrons (-ve) towards nucleus result in decreasing atomic size or decrease atomic radius.
In a Group- Atomic radius increases as we move from top to bottom in a group, because new shells are added which increases distance between nucleus and outermost electrons.

Metallic and Non-metallic Properties

                                                Elements towards left hand side in periodic table are metals while elements towards right hand side in periodic table are non-metals. Elements which separate metals and non-metals have the properties of the both metals and non-metals are known as Metalloids or Semi-Metals.

Example of Metals- Na, Mg, Al, Fe

Example of Non-metals- S, Cl, F, Br

Examples of Metalloids or Semi-Metals- B, Si, Ge, As, Sb, Te, Po

In a Period- Metallic character decreases and Non-metallic character increases as we move from left to right in a period because tendency to lose valence electrons  decreases due to increasing nuclear charge as we move from left to right in a period.
In a Group- Metallic character increases and Non-metallic character decreases as we move from top to bottom in a group because tendency to lose valence electrons increases due to increasing valence shells (i.e. increasing distance between nucleus and outermost electron) on moving from top to bottom in a group.
Metals are electropositive as they forms bonds by loosing electrons while Nonmetals are electronegative as they forms bonds by gaining electrons.
In general cases, oxides of metals are basic in nature while oxides of non-metals are acidic in nature.

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