Chemistry - Urgent - help Question in ppr 2

[moon]

plz help me to solve this question. thanx in advance.

element       Atomic radius/pm          Ionic radius/pm

lithium                   152                   
sodium                  186                       95
potassium              227                      138

[elemis]

Is the answer 59 ?

[moon]

Is the answer 59 ?

No Ari the answer is 78.

[iluvme]

(95/186)*152

[Deadly_king]

plz help me to solve this question. thanx in advance.

element       Atomic radius/pm          Ionic radius/pm

lithium                   152                   
sodium                  186                       95
potassium              227                      138

Hmm..............are you sure we need to find the ionic radius exactly?

Or is it just an estimate?

Koz i've never come across such a question.

[moon]

it just estimate.

[yasser37]

I've never seen this but

(95/186) * 152

[Deadly_king]

it just estimate.

Hehe.............now it's simpler.

First you should note that all of them are in Group 1. Hence their outermost electrons lie in an s-orbital.

However as we move down the group from lithium to potassium, the electric force between the positively charged nucleus and the outermost electron decreases since there is more shielding effect by the other preceding shells.

Moreover lithium has electronic configuration of 1s²2s¹. Losing one electron to form its corresponding Li⁺ ion will cause the electric force between the nucleus and the remaining two electrons from the 1s orbital to increase.

So ionic radius decreases. However when compared to sodium and potassium, this decrease is low since the electric force involves less protons(Li has only 3 protons while sodium has 11).

Decrease for sodium was (186 - 95) = 91.

For lithium, this decrease would be much lower, lets say about 70.
Hence ionic radius comes out to be around 80.