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SS3: CHEMISTRY - 2ND TERM

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  1. Quality of Petrol (Octane Number)| Week 1
    1 Topic
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    1 Quiz
  2. Natural Gas | Week 2
    3 Topics
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    1 Quiz
  3. Introduction to Metals | Week 3
    3 Topics
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    1 Quiz
  4. The Alkali Metals | Week 4
    4 Topics
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    1 Quiz
  5. Alkaline Earth Metals | Week 5
    4 Topics
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    1 Quiz
  6. Aluminium & Tin | Week 6
    3 Topics
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    1 Quiz
  7. Transition Metals of the First Series | Week 7
    4 Topics
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    1 Quiz
  8. Ethical, Legal & Social Issues | Week 8
    3 Topics
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    1 Quiz
  9. Fats & Oils - Soaps & Detergents | Week 9
    4 Topics
  10. Giant Molecules | Week 10
    6 Topics



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The elements of the first transition series are the d – block elements of the periodic table which include the elements Scandium through to Zinc.

transition metals dblock

Across the transition series, from left to right, electrons are added to fill up the inner d-orbital of the elements. Elements with completely filled or exactly half-filled d-subshell exhibits increased stability. 

Variable Oxidation States:

Transition elements exhibit variable oxidation states. This is because the energy difference between the 3d and 4s electrons is very little. In order to attain a noble configuration, the transition elements can lose a variable number of electrons from the 3d and 4s orbitals, thus, leading to a variable oxidation state. E.g. Ti forms +4 and +3; V forms +5 and +4; Fe forms +6, +3 and +2 oxidation states.

Electronic structure of the transition elements of the first series 

At. No.SymbolElectronic ConfigurationOxidation state
21Sc[Ar] 4s2 3d1+3
22Ti[Ar] 4s2 3d2+2, +3, +4
23V[Ar] 4s2 3d3+2, +3, +4, +5
24Cr[Ar] 4s1 3d5+2, +3, +6
25Mn[Ar] 4s2 3d5+2, +3, +4, +6, +7
26Fe[Ar] 4s2 3d6+2, +3
27Co[Ar] 4s2 3d7+2, +3
28Ni[Ar] 4s2 3d8+2, +3, +4
29Cu[Ar] 4s1 3d10+1, +2
30Zn[Ar] 4s2 3d10+2

Formation of Coloured ions:

Ions of transition elements are often coloured. This is because when white light shines on a transition metal compound, some of the energies of these coloured components are absorbed resulting in the excitation of 3d electrons. The transmitted colour becomes the colour of the transition metal ion. E.g. the colour of Ti3+ is violet/purple; Cr2+ is blue; Cr3+ is violet/green; Cr6+ is orange; Fe2+ is green; F3+ is reddish-brown; Mn2+ is pink, and so on.

Catalytic Activity:

Most Transition elements are used as catalysts in finely divided form. The ease with which their ion changes their oxidation state, and the availability of partially filled 3d orbital which allows the exchange of electrons to and from the molecule enable them to act as a catalyst. E.g. finely divided iron is used as a catalyst in the Haber process; Ni is used as a catalyst in the hydrogenation of ethene to ethane. V2O5 catalyst is used to convert SO2 oxide to SO3; Manganese (IV) oxide is used as a catalyst in the production of oxygen from KClO3.

Formation of Complex ion:

In transition elements, the atomic sizes are approximately the same because electrons are being added to the inner 3d orbital after an outer 4s orbital has been filled. This gives rise to the formation of alloys, salts, and complexes. Examples of complex ions are, Fe[CN]63-, Fe[CN]64-, [Cu(NH3)4]2-, etc. Examples of alloys are brass, steel, etc.

Paramagnetism:

This is the ability of an element to be attracted by a magnetic field. This is because of the presence of unpaired electrons in its orbital. For example, Iron is paramagnetic because only one of the 3d electrons is paired. The other four are single electrons. Fe3+ and Mn2+ experience the strongest paramagnetic effect because they have the highest number of unpaired 3d electrons, while Sc3+ and Zn2+ express the weakest paramagnetic effect between the numbers of unpaired 3d electrons is zero.

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