effective nuclear charge on the valance electrons increases. A similar trend is also observed in group . The remaining groups ( to ) follow the general trend. In these groups, the ionisation enthalpy decreases, as we move down the group.
Here, poor shielding effect of d- and f-electrons are overcome by the increased shielding effect of the additional p-electrons. The ionisation enthalpy of elements in successive groups is higher than the corresponding elements of the previous group as expected. . .
Electronegativity As we move down the th group, the electronegativity first decreases from boron to aluminium and then marginally increases for Gallium, thereafter there is no appreciable change. Similar trend is also observed in th group as well. In other groups, as we move down the group, the electro negativity decreases. This observed trend can be correlated with their atomic radius.
. . Anomalous properties of the first elements: In p-block elements, the first member of each group differs from the other elements of the corresponding group. The following factors are responsible for this anomalous behaviour.
. Small size of the first member . High ionisation enthalpy and high electronegativity . Absence of d orbitals in their valance shell The first member of the group , boron is a metalloid while others are reactive metals.
Moreover, boron shows diagonal relationship with silicon of group . The oxides of boron and silicon are similar in their acidic nature. Both boron and silicon form covalent hydrides that can be easily hydrolysed. Similarly, except boron trifluoride, halides of both elements are readily hydrolysed.
- - - - In group , the first element carbon is strictly a nonmetal while other elements are metalloids (silicon & germanium) or metals (tin & lead). Unlike other elements of the group carbon can form multiple bonds such as C=C, C=O etc... Carbon has a greater tendency to form a chain of bonds with itself or with other atoms which is known as catenation. There is considerable decrease in catenation property down the group (C>>Si>Ge≈Sn>Pb).
In group also the first element