Electron configuration of Tungsten (W) compared to Chromium (Cr) [ENDORSED]
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Electron configuration of Tungsten (W) compared to Chromium (Cr)
Hi, in class I learned that there is an electron configuration exception for Chromium where the electron from the 4s-sublevel is added to the 3d-sublevel instead, which makes the configuration to be [Ar] 3d^5 4s^1. However, I was looking online and found that the electron configuration for Tungsten (W), which is in the same group as Cr, is [Xe] 4f^14 5d^4 6s^2. Why doesn't the same rule apply to W? Wouldn't the energy be lower if it were in this configuration, [Xe] 4f^14 5d^5 6s^1? In Group 11, Copper (Cu), Silver (Ag), and Gold (Au) exhibit the same principle where the configuration is (n-1)d^10 (n)s^1. So, why doesn't the same principle for Cr work for W? Molybdenum (Mo) follows the same principle as Cr, but why not W? Thank you!
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Re: Electron configuration of Tungsten (W) compared to Chromium (Cr)
The reason for Tungsten not following the exception rule that Chromium does is not needed for our course. We only need to know the electron configurations for the first row of the d block, since this is a life science chemistry course.
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Re: Electron configuration of Tungsten (W) compared to Chromium (Cr) [ENDORSED]
Most likely due to the Lanthanide Contraction.
Because of the inefficient screening by the 4f14 e- the effective nuclear charge on the 5d and 6s is much larger than might be expected, and causes a huge contraction of the radii of the 3rd row TM atoms and ions. As can be seen the atomic radius of W is the same as that of Mo despite that W has 32 more e-. This in turn changes the relative energy for the different sub-shells in W.
Note that the electronic configuration also depends on the state of the atoms.
As a gas, in neutral atomic ground state, tungsten follows the Aufbau principle, so it has a completely filled 4f sub-shell, four electrons in the 5d sub-shell and two electrons in the 6s sub-shell.
In crystalline form however, the ground-state configuration in reality has five electrons in the 5d sub-shell and one electron in the 6s sub-shell.
So we see another example of very small energy differences between the shells and sub-shells for elements further down the periodic table.
And these small energy differences change as they are influenced by local electronic environment (in the gas versus sold phase).
I did not cover these topics in class as they are beyond the scope of our general chemistry class (where we cover the s-block, p-block, and the 1st row of the d-block (as announced in class)).
Tungsten (W) is way down in the 6th row of the periodic table.
Please note students will not be asked to give the electronic configuration of Tungsten (W). :-)
Because of the inefficient screening by the 4f14 e- the effective nuclear charge on the 5d and 6s is much larger than might be expected, and causes a huge contraction of the radii of the 3rd row TM atoms and ions. As can be seen the atomic radius of W is the same as that of Mo despite that W has 32 more e-. This in turn changes the relative energy for the different sub-shells in W.
Note that the electronic configuration also depends on the state of the atoms.
As a gas, in neutral atomic ground state, tungsten follows the Aufbau principle, so it has a completely filled 4f sub-shell, four electrons in the 5d sub-shell and two electrons in the 6s sub-shell.
In crystalline form however, the ground-state configuration in reality has five electrons in the 5d sub-shell and one electron in the 6s sub-shell.
So we see another example of very small energy differences between the shells and sub-shells for elements further down the periodic table.
And these small energy differences change as they are influenced by local electronic environment (in the gas versus sold phase).
I did not cover these topics in class as they are beyond the scope of our general chemistry class (where we cover the s-block, p-block, and the 1st row of the d-block (as announced in class)).
Tungsten (W) is way down in the 6th row of the periodic table.
Please note students will not be asked to give the electronic configuration of Tungsten (W). :-)
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