Archive for March, 2011

Fast Review – Chemical Bonding and Molecular Structure

1. The attractive force which holds together the constituent particles (atoms, ions or molecules) in chemical species is known as chemical bond.
2. Tendency or urge atoms of various elements to attain stable configuration of eight electrons in their valence shell is cause of chemical combination.
3. The principle of attaining a maximum of eight electrons in the valence shell or outermost shell of atoms is known as octet rule.
4. Electronic Theory: Kossel-Lewis approach to chemical Bonding: Atoms achieve stable octet when they are linked by chemical bonds. The atoms do so either by transfer or sharing of valence electrons. Inner  shell electrons are not involved in combination process.
5. Lewis Symbols or electron dot symbols: The symbol of the element represents the whole of the atom except the valence electrons  (i.e. nucleus and the electrons in the linear energy shells). The valence electrons are represented by placing dots (.) or crosses (x) around the symbol.
6. Significance of Lewis Symbols: The Lewis symbols indicate the number of
electrons in the outermost or valence shell which helps to calculate common or group valence.
7. The common valence of an element is either equal to number of dots or
valence electrons in the Lewis symbol or it is equal to 8 minus the number of
dots or valence electrons.
8. The bond formed by mutual sharing of electrons between the combining
atoms of the same or different elements is called a covalent bond.
9. If two atoms share one electron pair, bond is known as single covalent bond and is represented by one dash (–).

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How was the chemistry paper? (AISSCE 2011 Chemistry)

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AISSCE CHEMISTRY OLD QUESTION PAPERS 2007

WE ARE PROVIDING EIGHT SETS OF AISSCE CHEMISTRY 2007 QUESTION PAPERS FRO YOU TO PRACTICE

AISSCE CHEMISTRY 2007  QP SET 1

AISSCE CHEMISTRY 2007 QP SET 2

AISSCE CHEMISTRY  2007 QP SET 3

AISSCE CHEMISTRY2007  QP SET 4

AISSCE CHEMISTRY 2007 QP SET 5

AISSCE CHEMISTRY 2007 QP SET 6

AISSCE CHEMISTRY 2007 QP SET 7

AISSCE CHEMISTRY 2007 QP SET 8

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AISSCE Chemistry 2008 question paper and marking scheme

Question Papers AISSCE Chemistry 2008  Set-I Set-2 Set-3

Marking Schemes AISSCE Chemistry 2008  Set-I Set-2 Set-3

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Plustwo Chemistry – Some Questions for Practice

  1. An element ‘A’ exists as a yellow solid in standard state. It forms a volatile hydride ‘B’ which is a foul smelling gas
    and is extensively used in qualitative analysis of salts. When treated with oxygen, ‘B’ forms an oxide ‘C’ which is
    a colourless, pungent smelling gas. This gas when passed through acidified KMnO4 solution, decolourises it. ‘C’
    gets oxidized to another oxide ‘D’ in the presence of a heterogeneous catalyst. Identify A,B,C,D, and also give the
    chemical equation of reaction of ‘C’ with acidified KMnO4 solution and for conversion of ‘C’ to ‘D’.
  2. (a) An organic compound ‘A’ with molecular formula C5H8O2 is reduced to n-pentane on treatment with Zn-Hg/
    HCI. ‘A’ forms a dioxime with hydroxylamine and gives a positive lodoform test and Tollen’s test. Identify the
    compound A and deduce its structure.
    (b) Write the chemical equations for the following conversions:
    (not more than 2 steps)
    (i) Ethyl benzene to benzene
    (ii) Acetaldehyde to butane – 1, 3 – diol
    (iii) Acetone to propene 5
  3. Give reasons for the following:
    (a) Transition metals have high enthalpies of atomization.
    (b) Among the lanthanoids, Ce(III) is easily oxidised to Ce(IV).
    (c) redox couple has less positive electrode potential than couple.
    (d) Copper (I) has d10 configuration,while copper (II) has d9 configuration, still copper (II) is more stable in
    aqueous solution than copper (I).
    (e) The second and third transition series elements have almost similar atomic radii.
  4. (a) A blackish brown coloured solid ‘A’ when fused with alkali metal hydroxides in presence of air, produces a
    dark green coloured compound ‘B’, which on electrolytic oxidation in alkaline medium gives a dark purple coloured
    compound C. Identify A, B and C and write the reactions involved.
    (b) What happens when an acidic solution of the green compound (B) is allowed to stand for some time? Give the
    equation involved. What is this type of reaction called?
  5. (a) Calculate the standard free energy change for the following reaction at 250C
    Predict whether the reaction will be spontaneous or not at 250C. Which of the above two half cells will act as an
    oxidizing agent and which one will be a reducing agent?
    (b) The conductivity of 0.001M acetic acid is 4 x 10-5S / cm. Calculate the dissociation constant of acetic acid, if
    for acetic acid is 390. 5S cm2/mol.

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