attraction between the outer (or valence) electrons and the nucleus increases as the atomic radius decreases in a period. The electronegativity also increases. On the same account electronegativity values decrease with the increase in atomic radii down a group. The trend is similar to that of ionization enthalpy.
Knowing the relationship between electronegativity and atomic radius, can you now visualise the relationship between electronegativity and non-metallic properties? Non-metallic elements have strong tendency Fig. . The periodic trends of elements in the periodic table Table .
(a) Electronegativity Values (on Pauling scale) Across the Periods Atom (Period II) Be B C N O F Electronegativity . . . .
. . . Atom (Period III) Mg Al Si P S Cl Electronegativity .
. . Table . (b) Electronegativity Values (on Pauling scale) Down a Family Atom (Group I) Electronegativity Value Atom (Group ) Electronegativity Value .
At . to gain electrons. Therefore, electronegativity is directly related to that non-metallic properties of elements. It can be further extended to say that the electronegativity is inversely related to the metallic properties of elements.
Thus, the increase in electronegativities across a period is accompanied by an increase in non-metallic properties (or decrease in metallic properties) of elements. Similarly, the decrease in electronegativity down a group is accompanied by a decrease in non-metallic properties (or increase in metallic properties) of elements. All these periodic trends are summarised in Figure . .
. . Periodic Trends in Chemical Properties Most of the trends in chemical properties of elements, such as diagonal relationships, inert pair effect, effects of lanthanoid contraction etc. will be dealt with along the discussion of each group in later units.
In this section we shall study the periodicity of the valence state shown by elements and the anomalous properties of the second period elements (from lithium to fluorine). (a) Periodicity of Valence or Oxidation States The valence is the most characteristic property of the elements and can be understood in terms of their electronic configurations. The