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Molecular Orbital Theory To describe the covalent bond formation and nature of electron sharing, two theories have been proposed: Valence Bond Theory (VBT) and Molecular Orbital Theory (MOT). In Valence Bond Theory , only the half filled orbitals of valence shell take part in bond formation and the remaining orbitals retain their identity. But Molecular Orbital Theory (MOT) suggests the combination of all atomic orbitals having comparable energy and proper symmetry. Molecular Orbital Theory (MOT) was developed by F. Hund and R.S Mulliken in 1932. Main postulates of this theory are : 1. Atomic orbitals of comparable energy and proper symmetry combine together to form molecular orbitals. 2. The movement of electrons in a molecular orbital is influenced by all the nuclei of combining atoms. (Molecular orbital is poly centric in nature) 3. The number of molecular orbitals formed is equal to the number of combining atomic orbitals. When two atomic orbitals (AO's) combine t...

Definition of Heisenberg's Uncertainty Principle According to Heisenberg's uncertainty principle, it is not possible to determine precisely both the position and momentum (or velocity) of a moving microscopic particle, simultaneously with accuracy. Mathematical Expression of Heisenberg's Uncertainty Principle ▵x .▵p => h / 4π Where  ▵x is uncertainty with regard to the position and ▵p is uncertainty with regard to the momentum of the particle. If ▵x is very small ▵p would be large , that is , uncertainty with regard to momentum will be large. On the other side if we attempt to find out the momentum exactly the uncertainty with regard to position will be large. Explanation of   Heisenberg's Uncertainty Principle To determine the position of a small body like electron, it has to be illuminated with electromagnetic radiation. Low energy radiations like ordinary light waves cannot be used to illuminate a small body like electron, since the size of the ...

De-Broglie Hypothesis In 1924, de-Broglie proposed that matter has a dual character , as wave and as particle . In Bohr theory, electron is treated as particle. But according to De-Broglie, electron has a dual dual character; both as a material particle and as a wave. He derived an expression for calculating the wave length 'λ' of a particle of mass 'm'  moving with velocity 'v'. According to this, wave length = λ =  h / mv  , where 'h' is Planck's constant This is equation is known as De-Broglie's equation and it is an expression for wave - matter dualism . The waves associated with particles in motion are called matter waves or De-Broglie waves . They differ from electromagnetic radiations. They have lower velocities, and no electrical and magnetical fields associated with them. Derivation of  De-Broglie's equation The de-Broglie's equation can be derived by using the mass energy relationship suggest...

Properties of Potassium permanganate (KMnO 4 ) 1. Potassium permanganate (KMnO 4 ): Action of Heat Potassium permangante on strong heating gives potassium manganate, manganese dioxide and oxygen. 2 KMnO 4 ----------> K 2 MnO 4 + MnO 2 + O 2 2. Oxidising properties of Potassium permanganate (KMnO 4 ) Potassium permanganate is a powerful oxidizing agent in alkaline or acidic solution. The relevant half reactions are: 1. Alkaline medium (pH > 7) MnO 4 - + 2H 2 O + 3 e - ----------> MnO 2 + 4OH - 2. Acidic medium (pH <7) MnO 4 - + 8H + + 5e - ----------> Mn 2+ + 4H 2 O A few important oxidizing reactions of Potassium permanganate ( KMnO 4 ) 1. In acidic medium potassium permanganate oxidizes green ferrous salts to yellow ferric salts MnO 4 - + 8H + + 5Fe 2+ ----------> 5Fe 3+ + Mn 2+ + 4H 2 O 2. in acidic medium potassium permanganate oxidizes oxalic acid or oxalate salts to CO 2 and water 2 MnO 4 - + 16H + + 5 C 2 O ...

Chemistry in Dyes Natural dyes are extracted from natural sources. They are used for making coloured fabrics. Probably, the earliest known natural dyes were indigo (a blue dye) and alizarin (a red dye). These were obtained from plants. Definition of Dyes A dye is a coloured substance that can be applied in solution or dispersion to a substrate, giving it a coloured appearance. Usually the substrate is a textile fiber , but it can also be paper, leather, hair, fur, plastic material, wax, a cosmetic base or a foodstuff. Now a days synthetic dyes are used for dyeing purpose. Classification of Dyes Dyes are classified either according to their constitution or method of application. 1. Classification of dyes based on Constitution This classification is based on the distinguishing structural units present in the dye. 1. Azo 2. Nitro 3. Phthalein 4. Triphenyl Methane 5. Indigoid 6. Anthraquinone 2. Classification of dyes based on Application Depending upon the process of application the dyes ...

Vat Dyes Vat dyes are insoluble in water and cannot be used directly for dyeing. But on reduction to a leuco form (colour less), they become soluble in an alkali and acquire affinity for cellulose fibres. A solution of the leuco form can be applied for dyeing or printing. On oxidation the original insoluble dye is formed within th structure of the fibre. Indigo and indigosol O are dyes which belong to this class. Mordant Dyes Mordant dyes are primarily used for dyeing of wool in the presence of metal ions. The metal ion binds to the fabric and the dye acting as ligand co-ordinates to the metal ion. The same dye in the presence of different metal ions imparts different colours to the fabrics. The colours imparted by Alizarin in presence of different ions are given below Ions and colours Al3+ = Rose red Ba 2+ = Blue Cr 3- = Brownish red Mg 2+ = Violet Sr 2+ = Red For details about Dyes visit http://entrancechemistry.blogspot.com/2012/08/chemicals-in-every-day-life...

Fibre Reactive Dyes Fibre Reactive Dyes attach themselves to the fibre by an irreversible chemical reaction. The dyeing is fast and the colour is retained for a long time. The bonding is through the substitution of leaving group of dye via the hydroxy or amino group of fibres like cotton, wool or silk Insoluble Azo Dyes Insoluble Azo Dyes are obtained by coupling phenols, naphthols, arlamines, amino naphthols adsorbed on the surface of a fabric with a diazonium salt. Over 60% of the dyes used are Azo dyes . Cellulose, silk, polyester, nylon, polypropylene, polyurethanes, poly acrylonitriles and leather can be dyed by using these dyes. Azo dyes also find use in cosmetics, drugs, biological stains and as indicators in chemical analysis. Use of such dyes for colouring of food stuffs is not permitted . To know classification of dyes visit Chemicals in every day life: Dyes

Direct Dyes Direct dyes are water soluble dyes. As the name suggests, these dyes are directly applied to the fabric from aqueous solution and are practically suitable for fabrics like cotton, rayon, wool, silk and nylon which from hydrogen bonds with water. Martius yellow and congo red are important example of this class of dyes. Disperse Dyes Disperse Dyes in the form of minute particles of a suspension diffuse into the fabric, get fixed and impart colour. Such dyes are used for dyeing synthetic fibres like polyesters, nylon and polyacrylo nitrile . Many anthraquinone disperse dyes are suitable for application to synthetic polyamide fibres. T o know more about Dyes visit Chemicals in every day life: Dyes

Acid Dyes Acid dyes are usually salts of sulphonic acid and can be applied to wool, silk, polyurethane fibres and nylons. The affinity of acid dyes for nylon is higher than that for other types because polycaprolactum fibers fibers contain a higher proportion of free basic amino groups. Acid dyes do not have affinity for cotton. Orange-1 is a versatile acid dye. Basic Dyes Basic dyes contain amino group which in acid form water soluble salts. These dyes get attached to the anionic sites present on the fabrics. Such dyes are used to dye reinforced nylons and polyesters. Aniline yellow and malachite green belong to this class of dyes. To Know more about dyes visit Chemicals in every day life: Dyes