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(a) Describe the following characteristi...

(a) Describe the following characteristics of the first series (Sc to Zn)
(i) Atomic radil, (ii) Oxidation states (iii) Ionisation enthalpies.
(b) Name an important alloy which contains some of the lanthanoid metals. Mention its two uses.

Text Solution

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(a) (i) Atomic radii : From scandium to chromium atomic size decreases, increases in manganese and remains constant in Fe, Co, Ni, then increases in Cu and Zn.
The atomic radius decreases in a period in the begining because with increase in atomic number, the nuclear charge goes on increasing progressively. The shielding effect of d-electrons is so small so that the net electrostatic attraction between the nuclear charge and the outermost e-increases consequently the atomic radius decreases, as the number of d-electrons increases. This neutralizes the effect of increased nuclear charge due to increase in atomic number and consequently atomic radius remain almost unchanged after chromium Towards the end of the series there is increased electron-electron replusion between the added electrons in the same orbital which exceed the attractive forces due to increased nuclear charge and their size increases.
(ii) Oxidation states: The transition elements exhibit a variety of oxidation states in their compounds. This is due to the fact that (n-1)d-orbitals are of comparable energy to rs orbitals and therefore some or all of the (n - 1)d electrons can be used along with as electrons in compound formation. Some common oxidation states exhibited by elements of first transition series are listed below:

(The values in parentheses are less common oxidation states)
(iii) Ionisation enthalpy. The ionisation enthalpy of transition elements lie between those of s-block and p-block elements. They are higher than those of s-block elements and lower than those of p-block elements.
(b) Lanthanoids find special use for the production of alloy steel for plates and pipes called misch metals. Misch metal contains lanthanoid metal (95%) + iron (5%) and traces of S, C, Ca, Al. It is used in magnesium based alloy to produce bullets, shells, lighter flint.
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