CBSE Class 11-science Answered

Electronegativity decreases with an increase in atomic radius. With an increase in the atomic number, the atomic radius increases. Thus, the tendency to attract a shared pair of electrons decreases, and hence, electronegativity decreases down the group.

Electronegativity decreases down the group, i.e. from fluorine to astatine.

Fluorine is much smaller in size as compared to chlorine and thus has a greater tendency to attract electrons in a bonded pair more easily than chlorine. Hence, fluorine is more electronegative than chlorine.

Flourine is more electronegative than chlorine because

(i) Zeff (effective nuclear charge) is higher

(ii) smaller atomic size 

(ii) Greater ionisation potential