11th Class Chemistry Classification of Elements and Periodicity in Properties

  • question_answer 83)   First member of each group of representative elements (i.e., s and p-block elements) shows anomalous behaviour. Illustrate with two examples.

    Answer:

      In the case of representative elements, the first element in each of the group, i.e., lithium in the first group, beryllium in the second group and boron to fluorine in the groups 13 to 17 differ in many respects from the other members of their respective groups. This behaviour is attributed to following reasons: (a) small atomic radius of the atom, (b) high electronegativity, (c) non-availability of d-orbitals in the valency shell, (d) tendency to form multiple bonds, (e) high charge/radius ratio. Examples: Li is the first member of first group. It shows properties different than other alkali metals such as: (a) It does not impart colour to the flame like other alkali metals. (b) Its compounds show some what covalent nature while compounds of alkali metals are ionic. (c) it is more harder and lighter than other alkali metals. (d) It is the only alkali metal which directly combines with nitrogen. (e) \[LiHC{{O}_{3}}\] is not known in solid state as other bicarbonates of alkali metals are known. Carbon being the first member of its group shows the following unique properties: (a) It is the hardest and has highest melting and boiling points among the elements of group 14. (b) Its maximum covalency is 4. (c) It has maximum catenation property. It can form multiple bonds. (d) It has highest ionisation energy and most electronegative element of group 14. (e) Carbon dioxide, is a gas while the dioxides of other elements are solids.

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