Dear manisha, An increase in atomic radii is linked to an increase (more positive) electron gain enthalpy. Electron gain enthalpy becomes more negative (decreases) with increase in atomic number (decrease of atomic radii) across a period. It is easier to add an electron to smaller atom as it is closer to the atomic nuclei.
experts , can you please explain me the exact explaination for decrease in enthalpy in period , as you said it also linked with increase in atomic radii. but atomic radii decrease in period so it linked with the increase in atomic radii.
Dear manisha, The stronger is interaction between atom and electron the more energy is released. The value of enthalpy is negative ("-") due to the loss of energy. So, more negative value means more energy released. The value of enthalpy (i.e. group) becomes less negative or even positive ("+"). It means that enthalpy (in group or period) is changed from negative to positive values. So, mathematically its value [b]increases[/b] (from "-" to "+") though the absolute amount of released energy decreases.
thankyou for good answer but i did not get the excat reason that why it increase in group ,as atomic size increases down the group so interaction between nucleus and atom become weaker than ....what happened i can't understand.....so please explain me again.