Atomic Theory question

[MDPhDJourney]

For transition metals, why does half-filled stability (5 electrons in the d-orbital) result in a larger radius?


Thanks!
MDPhDJourney

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[dartmed]

For transition metals, why does half-filled stability (5 electrons in the d-orbital) result in a larger radius?


Thanks!
MDPhDJourney

Because adding an electron into the d-orbital would increase the radius as d-orbital is farther away from the nucleus. I think...

 

[dranet]

For transition metals, why does half-filled stability (5 electrons in the d-orbital) result in a larger radius?


Thanks!
MDPhDJourney

Are you sure you have this right??
Atomic size is attributed to the net nuclear charge and the electron/electron repulsion. The former pulls electrons towards the +ve nucleus whilst the latter has over come that and electron/electron repulsion increase the Atomic size. If you check atomic radii for d-group you will see they decrease left to right until the last few where the radii starts to increase again. This q tests effective nuclear charge, another MCAT love affair.

 

[MedPR]

Don't all the transition metals follow the trend of increasing atomic radii from right to left across a period? The radii decreases left to right because as you move left to right you add protons to the nucleus. The additional proton means additional attraction of the electrons to the central nucleus, thus pulling the electrons in and reducing the radius.

You probably know that the ionization energy increases from left to right across a period. This is in part due to the larger number of protons in the nucleus that are attracting or holding tighter to the electrons in their cloud, thus making it harder to abstract an electron.

 

[chiddler]

Calculated

And empirical

Not much changes when they're half full but they do change drastically when their d shell is 9/10 filled. Sup with that?

 

[Ssina]

I think OP might be referring to e.g. when we are writing the electron config for Cr we write it as 3d5 instead of 3d4 and saying it is more stable and has a smaller radius... and if so, then you have to consider where the electron came from that made it 3d5 instead of 3d4.... and it was from the 4s orbital... which is a bigger n.... so we technically moved an electron from n=4 to n=3 (and from -s- orbital to a -d- orbital)

 

[MedPR]

Calculated

And empirical

Not much changes when they're half full but they do change drastically when their d shell is 9/10 filled. Sup with that?

Where do you see a drastic change when the d shell is 9/10 filled?

Cu is 4s2 3d9 (actually 4s1 3d10) and has atomic radius of 145. Zn is 4s2 3d10 and has radius of 142

In 5s, Ag and Cd differ by 4 and in 6s Au and Hg differ by 3.

 

[chiddler]

Where do you see a drastic change when the d shell is 9/10 filled?

Cu is 4s2 3d9 (actually 4s1 3d10) and has atomic radius of 145. Zn is 4s2 3d10 and has radius of 142

In 5s, Ag and Cd differ by 4 and in 6s Au and Hg differ by 3.

Should we be paying attention to calculated or empirical? I thought empirical might be more telling.

I suppose I should of said around d9, excluding copper:

Pd --> Ag increases.

Au --> Hg increases.

It seems that a lot of the larger atoms seem to be very sluggish or unlike smaller atoms in their atomic radius change. Perhaps that is not relevant to mcat...

 

[MedPR]

Should we be paying attention to calculated or empirical? I thought empirical might be more telling.

I suppose I should of said around d9, excluding copper:

Pd --> Ag increases.

Au --> Hg increases.

It seems that a lot of the larger atoms seem to be very sluggish or unlike smaller atoms in their atomic radius change. Perhaps that is not relevant to mcat...

Oh, yea I was looking at calculated. I have no idea I think if we know the trends, why the are trends, and how each one interrelates with the others, we will be fine. Any exceptions will probably be explained in a passage.

 

[MedPR]

I think OP might be referring to e.g. when we are writing the electron config for Cr we write it as 3d5 instead of 3d4 and saying it is more stable and has a smaller radius... and if so, then you have to consider where the electron came from that made it 3d5 instead of 3d4.... and it was from the 4s orbital... which is a bigger n.... so we technically moved an electron from n=4 to n=3 (and from -s- orbital to a -d- orbital)

But does 4s1 3d5 have a larger radius than 4s2 3d4? Wouldn't the 4s1 atom have less shielding and therefore have a smaller radius than the 4s2 atom?

 

[Ssina]

But does 4s1 3d5 have a larger radius than 4s2 3d4? Wouldn't the 4s1 atom have less shielding and therefore have a smaller radius than the 4s2 atom?

I think you mean more shielded from protons, since we added the electron to 3d, so it's larger
mmm yeah I kinda thought about that too!! lol idk I went from lower in energy, but this makes more sense

 

[MedPR]

I think you mean more shielded from protons, since we added the electron to 3d, so it's larger
mmm yeah I kinda thought about that too!! lol idk I went from lower in energy, but this makes more sense

I meant less shielded. But maybe I am misunderstanding the concept. I thought the shielding electrons were the ones in between the nucleus and the valence shell, so the 4s electrons shield the 3d electrons from the attractive force due to the protons in the nucleus.. Thus, if you excite a 4s electron and move it to 3d, haven't you removed a shielding electron, thereby reducing the amount of shielding and decreasing the atomic radius?

 

[Ssina]

I meant less shielded. But maybe I am misunderstanding the concept. I thought the shielding electrons were the ones in between the nucleus and the valence shell, so the 4s electrons shield the 3d electrons from the attractive force due to the protons in the nucleus.. Thus, if you excite a 4s electron and move it to 3d, haven't you removed a shielding electron, thereby reducing the amount of shielding and decreasing the atomic radius?

yes your right... I keep confusing myself
that's what I was tryin to say

 

[MedPR]

yes your right... I keep confusing myself
that's what I was tryin to say

Just one of those days Don't sweat it, you helped me by making me explain it