The electron gain enthalpies of some of the elements of second gp. i.e o and F Are, however less negative than the corresponding elements (i.e S and cl) of the third. Why?
Answers
Answer:
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Answer:
They are anomalies. This occurs usually because of the lack of d orbitals among the second period elements.
Now, to answer your question,
we know that atomic size decreases across the period due to the increased nuclear pull. This means that atoms like oxygen and fluorine are very small in size. Being very small in size,you might think that the electrons will get added easily in the orbits but this does not happen. What actually happens is, when you add an electron to oxygen or fluorine, the electrons already present in the atom produce repulsive forces hence making it difficult to add the electron into the atom.
In case of the 3rd period elements,sulphur and chlorine,their size is much larger and hence they provide less repulsion compared to oxygen and fluorine.
Hope this helps :)