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Question

Which of the following order of radii is correct?


A

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B

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C

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D

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Solution

The correct option is B


Lets write the electronic configurations of each species.

Li Ts22s1 Be 1s22s2

Mg 1s22s22p63s2

H+ 1s0 Li+ 1s2 H 1s2

O 1s22s22p4 F 1s22s22p5 Ne 1s22s22p6

Na+ 1s22s22p6 F 1s22s22p6 O2 1s22s22p6

Now, we know that

Along a periodfrom Left to Right, Atomic Radius decreases because effective nuclear charge increases, on the valance electrons resulting in the increased attraction of electrons to the nucleus.

Down the group fromTop to Bottom, Atomic Radius increases because the principal quantum number (n) increases and the valance electrons are farther from the nucleus.

Now, try to remember from the videos, for isoelectronic species, the more cationic charge on the atom, lesser will be then ionic radius.

More the ionic charge on the atom, more will be the ionic radius.

Now, In option (a), the correct order will be Mg > Li > Be

Because Mg has principal quantum number (n) = 3 and Be gas n = 2

Among Li and Be, Li > Be because along a period from Left to Right, atomic radius increased

Now, In option (b)

H+ < Li+ < H

For H+, there are no electrons, so no atomic radius. In case of Li+ and H, Li+ < H,

In option (c), the correct order will be

Ne > O > F

Because for noble gases (Ne), we consider Van der Waal's radius which is larger than covalent radius.

Between O and F, O > F because Along a periodfrom Left to Right, Atomic Radius decreases because effective nuclear charge increases, on the valance electrons resulting in the increased attraction of electrons to the nucleus.

In option (d), the correct order will be

O2 > F > Na+

Because, Now, try to remember from the videos, for isoelectronic species, the more cationic charge on the atom, lesser will be then ionic radius.

More the ionic charge on the atom, more will be the ionic radius

. Now, In option (a), the correct order will be Mg > Li > Be

Because Mg has principal quantum number (n) = 3 and Be gas n = 2

Among Li and Be, Li > Be because along a period from Left to Right, atomic radius increased

Now, In option (b)

H+ < Li+ < H


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