Chemistry Podcast

Tuesday, 23 June 2015

Thomson model of atom and Rutherford’s nuclear model of atom

Thomson model of atom

=>  Give 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.
=>  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 nuclear model of atom

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 undeflected :
     2)    A small fraction of α- particles was deflected by small angles.
    3)    A very few α- particles (about 1 in 20000) 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 undeflected.
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 .

Sunday, 21 June 2015

Atomic Theory of matter, Cathode ray discharge tube experiments and Charge (e) to mass (me) ratio of electron

Atomic  Theory of matter :-

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

Cathode ray discharge tube experiments: - 

1.     Cathode rays start from cathode and move toward anode.
2.     These rays are not visible but there behaviour can be observed with fluorescent or phosphorus sent material.
3.     In the absence of magnetic or electric field these travels in strait lines
4.     In the presence or magnetic or electric field the behaviour of cathode rays in similar TO Negatively  charged  particles  which suggest that these rays contain negatively charge particles called electron
5.     Cathode rays (electrons) do not depend on  the martial of the electrode and  nature of the gas tin the tube so electro us are basic constituent of all atoms.

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

ð Measured by  J. J. Thomson (1897).
ð By using cathode ray tube ; applying electrical & magnetic field perpendicular to each other also perpendicular to path of electrons.
ð He proposed  deviation of particles from their path in presence of magnetic or electrical field depend upon the following
1.     Magnetic of  – ve  charge on particle
i.e. it 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. it strength of magnetic  field or voltage at electron is increases then deflection of                                            e-  also increases
        =>  value of e/me = 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/me
 We get,                 
MASS OF ELECTRON
             Me = 9.1094 ´ 10-31 kg

GATE Syllabus for Chemistry (CY)

PHYSICAL CHEMISTRY

Structure:Quantum theory: principles and techniques; applications to a particle in a box, harmonic oscillator, rigid rotor and hydrogen atom; valence bond and molecular orbital theories, Hückel approximation; approximate techniques: variation and perturbation; symmetry, point groups; rotational, vibrational, electronic, NMR, and ESR spectroscopy
Equilibrium: Kinetic theory of gases; First law of thermodynamics, heat, energy, and work; second law of thermodynamics and entropy; third law and absolute entropy; free energy; partial molar quantities; ideal and non-ideal solutions; phase transformation: phase rule and phase diagrams – one, two, and three component systems; activity, activity coefficient, fugacity, and fugacity coefficient; chemical equilibrium, response of chemical equilibrium to temperature and pressure; colligative properties; Debye-Hückel theory; thermodynamics of electrochemical cells; standard electrode potentials: applications – corrosion and energy conversion; molecular partition function (translational, rotational, vibrational, and electronic).
Kinetics: Rates of chemical reactions, temperature dependence of chemical reactions; elementary, consecutive, and parallel reactions; steady state approximation; theories of reaction rates – collision and transition state theory, relaxation kinetics, kinetics of photochemical reactions and free radical polymerization, homogeneous catalysis, adsorption isotherms and heterogeneous catalysis. 

INORGANIC CHEMISTRY

Main group elements: General characteristics, allotropes, structure and reactions of simple and industrially important compounds: boranes, carboranes, silicones, silicates, boron nitride, borazines and phosphazenes. Hydrides, oxides and oxoacids of pnictogens (N, P), chalcogens (S, Se & Te) and halogens, xenon compounds, pseudo halogens and interhalogen compounds. Shapes of molecules and hard- soft acid base concept. Structure and Bonding (VBT) of B, Al, Si, N, P, S, Cl compounds. Allotropes of carbon: graphite, diamond, C60. Synthesis and reactivity of inorganic polymers of Si and P.
Transition Elements: General characteristics of d and f block elements; coordination chemistry: structure and isomerism, stability, theories of metal- ligand bonding (CFT and LFT), mechanisms of substitution and electron transfer reactions of coordination complexes. Electronic spectra and magnetic properties of transition metal complexes, lanthanides and actinides. Metal carbonyls, metal- metal bonds and metal atom clusters, metallocenes; transition metal complexes with bonds to hydrogen, alkyls, alkenes and arenes; metal carbenes; use of organometallic compounds as catalysts in organic synthesis. Bioinorganic chemistry of Na, K. Mg, Ca, Fe, Co, Zn, Cu and Mo.
Solids:Crystal systems and lattices, miller planes, crystal packing, crystal defects; Bragg’s Law, ionic crystals, band theory, metals and semiconductors, Different structures of AX, AX2, ABX3 compounds, spinels.
Instrumental methods of analysis: Atomic absorption and emission spectroscopy including ICP-AES, UV- visible spectrophotometry, NMR,
mass, Mossbauer spectroscopy (Fe and Sn), ESR spectroscopy, chromatography including GC and HPLC and electro-analytical methods
(Coulometry, cyclic voltammetry, polarography– amperometry, and ion selective electrodes). 

ORGANIC CHEMISTRY

Stereochemistry: Chirality of organic molecules with or without chiral centres. Specification of configuration in compounds having one or more stereogeniccentres. Enantiotopic and diastereotopic atoms, groups and faces. Stereoselective and stereospecific synthesis. Conformational analysis of acyclic and cyclic compounds. Geometrical isomerism. Configurational and conformational effects on reactivity and selectivity/specificity.
Reaction mechanism: Methods of determining reaction mechanisms. Nucleophilic and electrophilic substitutions and additions to multiple bonds. Elimination reactions. Reactive intermediates- carbocations, carbanions, carbenes, nitrenes, arynes, free radicals. Molecular rearrangements involving electron deficient atoms.
Organic synthesis: Synthesis, reactions, mechanisms and selectivity involving the following-alkenes, alkynes, arenes, alcohols, phenols, aldehydes, ketones, carboxylic acids and their derivatives, halides, nitro compounds and amines. Use of compounds of Mg, Li, Cu, B and Si inorganic synthesis. Concepts in multistep synthesis- retrosynthetic analysis, disconnections, synthons, synthetic equivalents, reactivity umpolung, selectivity, protection and deprotection of functional groups.
Pericyclic reactions: Electrocyclic, cycloaddition and sigmatropic reactions. Orbital correlation, FMO and PMO treatments.
Photochemistry: Basic principles. Photochemistry of alkenes, carbonyl compounds, and arenes. Photooxidation and photoreduction. Di-π- methane rearrangement, Barton reaction.
Heterocyclic compounds: Structure, preparation, properties and reactions of furan, pyrrole, thiophene, pyridine, indole and their derivatives.
Biomolecules: Structure, properties and reactions of mono- and di-saccharides, physicochemical properties of amino acids, chemical synthesis of peptides, structural features of proteins, nucleic-acids, steroids, terpenoids, carotenoids, and alkaloids.
Spectroscopy: Principles and applications of UV-visible, IR, NMR and Mass spectrometry in the determination of structures of organic molecules.

Pattern for Single Paper MCQ test- NET Chemistry

UGC NET Chemistry (CY) Exam Patter

  • The MCQ test paper of chemistry shall carry maximum of 200 marks.
  • This exam shall be for duration of 3hrs.
  • The question paper shall be divided in three parts i.e.
    Part 'A' , Part 'B', Part 'C'
Part wise description of paper
  • Part 'A' shall be common to all subjects. This part shall be a test containing a maximum of 20 questions of General Aptitude. The candidates shall be required to answer any 15 questions of two marks each. The total marks allocated to this section shall be 30 out of 200
  • Part 'B' shall   contain subject-related conventional MCQs. The total marks allocated to this section shall be 70 out of 200. The maximum number of questions to be attempted shall be in the range of 20-35. 
  • Part 'C' shall contain higher value questions that may test the candidate's knowledge of scientific concepts and/or application of the scientific concepts. The questions shall be of analytical nature where a candidate is expected to apply the scientific knowledge to arrive at the solution to the given scientific problem.  The total marks allocated to this section shall be 100 out of 200.
  • Negative marking for wrong answers. 

DOWNLOAD MODEL QUESTION PAPER

Saturday, 20 June 2015

Laws of chemical combinations, Dalton’s Atomic Theory and Concentration expression methods

Laws of chemical combinations

      1)      Law of conservation of mass:- According to this law “matter can neither be created nor destroyed” Given by Antone Lovoisin in 1789.
    2)      Law of definite proportion:- According to this law “A given compound always contains exactly the same proportion of elements by weight known as law of definite proportion or law of definite composition” given by Joseph Proust in 1754-1826
     3)      Law of multiple proportion:- According to this law “if two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of small whole number” given by Dalton in 1803.
    4)      Gay lussac’s law of gaseous volume:- According to this law “gases combine or are produced in chemical reactions they do so in a simple ratio by volume provided to all gases are at the  same temperature and pressure” given by Gay Lussac’s in 1808.
    5)      Avogadro’s law:- According to this law “Equal volume of gases at same temperature & pressure should contain equal no. of molecules” given by Avogadro in 1811.

Dalton’s Atomic Theory

         i.            Matter consists of indivisible atoms.
       ii.            All the atoms of a element have identical properties (same properties) i.e. atoms of a element have same mass while atoms of different elements have different masses.
       iii .            Compounds formed when atoms of different elements combine in fixed ratio.
     iv.            Chemical reactions involve reorganization (rearrangement) of atoms.
Atomic mass unit = 1/12th mass of one carbon12 atom.
Molecular mass = It is the sum of atomic masses of the elements present in a molecule.
Mole :- It is the amount of substance equal to Avogadro no. (NA). = 6.022 ´ 1023 atoms/mole.
Molar mass:- Mass of one mol of a substances in gram is known as molar mass.
Mass % of an element = mass of that element in compound ´ 100/ molar mass of the compound.
Empirical formula :- It is the simplest whole no. ratio of various atoms present in a compound.
Molecular formula:- It is the exact no. of different types of atoms present in a molecule of a compound.

Concentration expression methods

                     i.          
                   ii.            Mole fraction :- If a substance ‘A’ is dissolved in ‘B’ and their no. of moles are nA and nB respectively.
MOLE FRACTION AND MOLARITY

NOTE:

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