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Calculating effective nuclear charge

by escryan
Tags: charge, effective, nuclear
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escryan
#1
Oct22-08, 10:51 PM
P: 13
1. The problem statement, all variables and given/known data

If ionization energy is 899.4 kJ/mol for Be, what is the effective nuclear charge?

2. Relevant equations
Zeff = Z - S

E=RH(Z2/n2) ??
E=RH(Zeff2/n2)??

3. The attempt at a solution

My attempted solution was subbing into
Zeff = Z - S
Zeff = 4 - 2
= 2

But I suspect that is wrong... because why ionization energy is given.. so shouldn't it be used in the calculation?

And somewhere I think I read that "S" was supposed to be a "constant" of some sort, and I just subbed 2 in because I thought that it was the number of electrons in the first orbital ?
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Borek
#2
Oct23-08, 03:03 AM
Admin
Borek's Avatar
P: 23,392
One of the equations you listed contains both ionization energy and effective nuclear charge, why don't you use it?
escryan
#3
Oct23-08, 04:27 AM
P: 13
Ah..
So subbing in values
E=899.4 kJ/mol
RH=2.178 x 10-21 kJ
n=1

I get Z2eff= 4.129 x 10 23 mol

How does one get to the units/value of Z2eff after this?

Borek
#4
Oct23-08, 04:53 AM
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P: 23,392
Calculating effective nuclear charge

Ionization energy was per mole, not per molecule.
escryan
#5
Oct23-08, 05:17 PM
P: 13
Oops, just noticed that "Z2eff= 4.129 x 10 23 mol " should actually read "Z2eff= 4.129 x 10 23 mol-1 "

I think that the italicized part is what confuses me the most -- what are the units for this portion? I'm going to take a guess that it is currently molecules/mol, but if so, is this always the case whenever expressing a value and the unit mol-1?

Like for this example, what was given was in kJ/mol. When the kJs were cancelled, what resulted was just mol-1...


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