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### Topic: quantum physics but a chemistry question  (Read 2550 times)

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#### studygirl

• Guest ##### quantum physics but a chemistry question
« on: June 22, 2005, 07:29:45 PM »
what is the longest wavelength seen in the visible absorption spectrum of Li2+ at ordirnary temperatures?
okay so i was given this equation to apply it to,

okay so i got
delta E=Ro (1/n^2-1/nf^2)
=2.18x10^-18J (1/inifinity- 1/3^2)   the three because 3 can be used for longest wavelegnth, and that is n=3
=-7.72x10^19
then ( the symbol that looks like a weird H)=ch/delta E
=3.00x10^8m/s x 6.63x10^-34  / (7.27x10^-19J
=2.735x10^-7m   x 10^9nm/1m
=273.5nm

what is the shortest wavelenth using the same equation?
delta E= Ro (1/n^2-1/nf^2)
=2.18x10^-18J (1/inifinity/1/2^2)
=-2.18X 10^-18 x 1/4
=5.45x10^-19J
then(weird H looking symbol)= ch/delta e
=3.00x10^8m/s x 6.63 x 10^-34 Js/(5.45x 10^19J
=3.65x10^-7m  x 10^9nm/1m
=365nm

then calculate the ionization energy of Li2+ refer to the exercise 8.55 for the equation needed, to allow for the difference between the nuclear charges of lithium and hydrogn

so....
En = -(2.18x10^-18J) Z^2(1/n^2)
n= principal quantum number
z=atomic number of the element
En= -(2.18x10^-18J)3^2(1/9^2)
but the answer doesnt make sense,
so either my lithium is incorrect,
but the lithium z= 3
and the n = 9 squared which is 81? ??
any help at all would be useful,
i was given these equations to use, so any help would be grateful
thank you

now i know this is wrong because i checked, so if possible is there an alternate
way of calculating this,
the numerbs i got above was from an example i got from my teacher,