3. Classification of elements and periodicity in properties — Chemistry STD 11 Science — Question

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Let us arrange the elements according to the way they are arranged in the periodic table.

Lithium ,Beryllium ,Boron ,Carbon ,Nitrogen ,Oxygen, Fluorine, Aluminium Chlorine

As we move from Lithium to fluorine the electron affinity increases and as we move from Fluorine to chlorine and further electron affinity decreases. Hence electron affinity of chlorine should be greater than oxygen and oxygen should be greater than nitrogen and nitrogen should be greater than aluminium. As we move down, the size increases, and due to that, the electron affinity decreases as it is the tendency to gain electrons. Metals do not gain electrons, nonmetals do. So, aluminum is at the last position.