Question

Calculate radius of orbital Li2+ ion in third orbital

Answer 1

Before i go into this question there may be doubts arising like why dont we calculate the radius of Li atom and why Li2+ only or why He2+ ion why not He .
Well for calculating the atomic radius we use the formula which was given bohr
and this formula works only for hydrogen and like hydrogen atoms so Li is not like Hydrogen atom but Li2+ ion resembles hydrogen atom hence this is main reason why we get such questions.(Note this formula is not good for atoms other than hydrogen but we consider it to be applicable also for hydrogen like atoms because it is very close to actual answer )

Let me come back to your question so to calculate the radius of the orbital os Li2+ ion in third orbital
we have a formula :-
r=0.529*n^2/Z ( if we use this formula we get the answer in angstorm )
here r= radius
n= orbit number
Z= atomic number

r = 0.529*3^2/3
r=0.529*9/3
r=0.529*3=1.587 angstorm

to convert angstorm to meter multiply by 10^-10
 therefore 1.587angstorm= 1.587*10^-10m

Hope this helped u :-)

Answer 2

r=0.529*n^2/z

z=3 for LI

n=3

r=0.529*9/3

r=1.587