Which of the following orders is correct for the size ? (1)Mg^(2+)ltNa^(+)ltF^(-)ltAl (2)Al^(3+)ltMg^(2+)ltLi^(+)ltK^(+) (3)Fe^(4+)ltFe^(3+)ltFe^(2+)ltFe (4)MggtAlgtSigtP

Which of the following orders is correct for the size ? (1)Mg^(2+)ltN

1.	Which of the following orders is correct for the size ? (1)Mg^(2+)ltNa^(+)ltF^(-)ltAl (2)Al^(3+)ltMg^(2+)ltLi^(+)ltK^(+) (3)Fe^(4+)ltFe^(3+)ltFe^(2+)ltFe (4)MggtAlgtSigtP
Answer» (1),(2)&(3) (2),(3) & (4) (1),(3) & (5) (1),(2),(3) & (4) Solution :(1)`Mg^(2+),Na^(+) and F^(-)` are isoelectronic and thus follows the order `._12 Mg^(2+) lt ._(11)Na^(+) lt ._9F^(-)` All belongs to third period and has no charge so itis largest. `Na^(+)=102` pm , `Mg^(2+)` =72 pm, Al=143 pm, `F^-`=133 pm. (2)`K^+` has more number of shells than `Mg^(2+)` and `Al^(3+)` .`Al^(3-)` and `Mg^(2+)` are isoelectronic but `Al^(3+)` has HIGHER nuclear charge so `Al^(3+) lt Mg^(2+) . Mg^(2+)` and `Li^(+)` has diagonal relationship.But due to +2 charge to +2 charge in `Mg^(2+)` , the `Mg^(2+)` is smaller than `Li^(+)`.Hence `Al^(3+)` is the smallest one. `K^(+)=1.38Å, Li^(2+)=0.76 Å, Mg^(2+)=0.72 Å, Al^(3+)=0.535 Å` (3)As the number of electrons are lost , the attraction between valence shell electrons and nucleus increases As a consequence of this the electrons are pulled CLOSER to the nucleus leading to the contraction in size of ions. (4)Across the period the nuclear charge increases and thus the size of atoms decreases, Mg=160 pm, Al=143 pm , Si=118 , P=110 pm