Question

Account for the following:
i) There is substantial decrease of ionization enthalpy from Mg to Ca but not so from Al
to Ga.
ii) The electron gain enthalpy value of fluorine is lesser than that of chlorine.
iii) Order of reactivity of group 1 elements increases down the group while that of group
17 elements decreases as we move from top to bottom.

Answer 1

Answer:

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Answer 2

Reasoning for the following has been given below:

Explanation:

• Ionization enthalpy of the main group elements decreases down the group because of the increase in atomic size and therefore there is a weak binding force with the nucleus.  Also because of the shielding or screening effect , the force of attraction with the valence electron decreases.

            However , from Al to Ga , Ga shows an increase in this is because                      it lies adjacent to 3d series and that results in poor shielding of d electron. Also size of Ga doesn't increase as much but the nuclear charge increases.

• Small size of fluorine atom results in strong interelectronic repulsions in small 2p orbitals of fluorine . This causes lesser attraction for the incoming electron. Therefore electron gain enthalpy of fluorine is less than chlorine.

•    The order of  reactivity of group 1 elements increases down the group because the size of atoms become bigger. Also the outer electron moves farther away from the nucleus which causes decrease in force of attraction between the nucleus and outermost electron.

        For group 17 elements , the atomic radii increases down the group and therefore the electronic energy level also increases. The larger separation between outermost electron and nucleus ( more electrons are present in between) causes gaining of an electron more difficult, therefore the atom is less reactive.