Understanding Electron Configurations - Help please!

[RyanJ]

Hi there everyone!

 

I've been reading up on electron configuration and I just don't understand it at all.

I know there are 4 shell types (s, p, d, f, and a hypothetical g). But I just don't undestand how to use these. Can someone explain this to me in a simple way?

 

e.g. I know that Hygrogen has the configuration of: 1S¹, Helium: 1S²but I don't understand how you'd do these as needed in say an exam.

 

I'm much appreciate it if someone could explain how you are supposed to work these out as needed - How am I supposed to know the configuration based on the proton number (Or the electron number because they are both the same unless its an ion...)?

 

Thanks for the help, a demonstration of the answer would also help a lot

 

Cheers,

 

Ryan Jones

[insane_alien]

you should be taught the principles behind the filling of the orbitals soon. they are usefull for representsing bonds without aa diagram

[RyanJ]

you should be taught the principles behind the filling of the orbitals soon. they are usefull for representsing bonds without aa diagram

 

Yea I know - we should be learning about it sometime in the next two weeks - I just like to learn ahead

 

Cheers,

 

Ryan Jones

[woelen]

Hi there everyone!

 

I've been reading up on electron configuration and I just don't understand it at all.

I know there are 4 shell types (s' date=' p, d, f, and a hypothetical g). But I just don't undestand how to use these. Can someone explain this to me in a simple way?

 

e.g. I know that Hygrogen has the configuration of: [b']1S¹[/b], Helium: 1S²but I don't understand how you'd do these as needed in say an exam.

 

I'm much appreciate it if someone could explain how you are supposed to work these out as needed - How am I supposed to know the configuration based on the proton number (Or the electron number because they are both the same unless its an ion...)?

 

Thanks for the help, a demonstration of the answer would also help a lot

 

Cheers,

 

Ryan Jones

Having a good understanding of orbitals allows you to predict chemical properties of compounds, the spatial geometry of compounds and it also is very helpful in understanding (and predicting) the formation of complexes. A forum like this is not a really good place to explain all this (that would result in a post of many many pages), but I suggest you to grab the book of Linus Pauling. It contains a good explanation of basic quantum mechanics and application of this on orbitals. Once you grasp that concept, you also can understand much more about orbital hybridization, which helps very much in understanding many (organic) reactions.

[RyanJ]

Having a good understanding of orbitals allows you to predict chemical properties of compounds, the spatial geometry of compounds and it also is very helpful in understanding (and predicting) the formation of complexes. A forum like this is not a really good place to explain all this (that would result in a post of many many pages), but I suggest you to grab the book of Linus Pauling. It contains a good explanation of basic quantum mechanics and application of this on orbitals. Once you grasp that concept, you also can understand much more about orbital hybridization, which helps very much in understanding many (organic) reactions.

 

Yea - funny I read something along those lines just a few kinutes ago (From one of the books you reccomended!)

 

Do you happen to know how you write these? Like how do you know how namy S fileds there are in an atom etc.?

 

Cheers,

 

Ryan Jones

[woelen]

When you have a single positive point charge and an electron 'orbiting' around the point charge, then the electron can only be in discrete energy levels.

 

In an atom, the nucleus can be regarded as a single point charge and the error introduced with this is VERY small. The nucleus is very small, compared to the total atom size.

 

Having said that, the motion of an electron around a nucleus can be described by means of a partial differential equation. By assuming certain forms of the solution, the problem is reduced to an eigenvalue problem, which has a discrete set of solutions. Such a solution is fully specified by four numbers:

1) The principal quantum number, which tells how far the electron is 'orbiting' around the nucleus. I.e. this tells something about the size of the orbital.

2) The angular quantum number, which tells something about the shape of the orbital.

3) The magnetic quantum number, which tells something about the orientation of the shape, described by number (2).

4) The electron spin.

 

The principal quantum number can be any positive integer and this number corresponds to the shell. Principal number 1 corresponds to shell 1, etc.

 

Shell 1 only supports one spherical orbital.

Shell 2 supports a shperical orbital and a lobe-shaped orbital.

Shell 3 supports a spherical orbital, a lobe-shaped orbital and a kind of cloves-shaped orbital.

Shell 4 supports a spherical orbital, a lobe-shaped orbital, a kind of cloves-shaped orbital and an even more complex form of orbitals.

Shell 5 ....

 

Now comes into play a lot of geometry. A sphere is symmetric about every plane which goes through its center and spheres of different orientation cannot be distinguished from each other, if they are totally featureless. So, for spherical orbitals, only one exists. So, each shell has precisely one spherical orbital.

 

The lobe-shaped orbital can have three orientations. If you fix one of them, then two perpendicular orbitals can be constructed, which are independent. So, three lobe-shaped orbitals can exist inside a single shell. For the cloves-shaped orbital there can be 5 different orientations, and for the even more complex one, there can be 7 different orientations.

 

A spherical orbital is called s-orbital.

A lobe-shaped orbital is called p-orbital.

A cloves-shaped orbital is called d-orbital.

The complex shaped orbital, allowed by shell 4 is called f-orbital.

In shell 5 there can also be a g-orbital, which is amazingly complex.

 

Now, summarizing:

 

Shell 1: s

Shell 2: s + 3p

Shell 3: s + 3p + 5d

Shell 4: s + 3p + 5d + 7f

Shell 5: s + 3p + 5d + 7f + 9g

 

Inside an orbital, there can be at most two electrons of opposite spin. This is due to the Pauli exclusion principle. Google this for more info.

 

Based on the above info, the shells can accomodate at max the following number of electrons:

 

1: 2

2: 8

3: 18

4: 32

5: 50

 

Now, let's look at a real atom, the element sodium:

 

Sodium is element 11, so there are 11 electrons. Two electrons go in shell 1, 8 electrons go in shell 2 and 1 electron goes in shell 3. First s orbitals are filled, then p orbitals.

 

So, we have configuration 1s2 2s2 2p6 3s1

 

In fact, 2p6 usually is written as 2px2 2py2 2pz2, indicating that there are three p-orbitals, perpendicular to each other, each filled with two electrons.

 

Now for calcium, which is element number 20. The first two electrons go in shell 1. The next 8 electrons go in shell 2. The next 8 electrons after that go in shell 3. And now we have a 'problem'. The next two electrons do not go in shell 3's d orbital, but in shell 4's s-orbital. So for calcium we have:

 

Ca: 1s2 2s2 2p6 3s2 3p6 4s2

 

When we go to element 21 (scandium), then the next electron is added to the d-orbital of shell 3:

 

Sc: 1s2 2s2 2p6 3s2 3p6 3d1 4s2

 

This is where the term 'transition metal' is coming from. While going from scandium to zinc, the 3d orbitals are filled and after zinc, the 4p orbitals are filled. There are two anomalies in the transition series, but for the time being it is best to skip that detail .

 

Why is the 4s orbital preferred over the 3d orbitals? This is something which only can be understood when quantummechanically, the energy levels in the atoms are computed and it appears that first filling the 4s orbitals is more favorable energetically.

 

With the next row of transition metals, a similar thing happens. First the 5s orbital is filled for Rb and Sr, and then the 4d orbitals are fileld for Y to Cd, after Cd the 5p orbitals are filled. So, here we see another strange thing. The 5p orbitals are preferred over the 4f orbitals. The last 6 elements of row 5 fill all three 5p orbitals.

 

In row 6, first the 6s orbital is filled for Cs and Ba, then the 4f orbitals are filled (these are the lanthanide elements), then the 5d orbitals are filled (these are the third row of transition elements) and finally, the 6p orbitals are filled, ending at Rn.

 

In row 7 again something like this happens. First the 7s orbital is filled, then the 5f orbitals and then it stops... we have entered the region where there are no more stable elements. In theory, here we would have completion of 6d orbitals and then completion of 7p orbitals. The g-orbitals are purely hypothetical, because these would only come up in a very long 8-th row of the periodic table.

 

With this theory in mind, you can now perfectly understand the shape of the periodic table. This is really beautiful. From underlying quantummechanics and orbital theory, the periodic table can be understood very nicely.

 

I hope that digesting this long post is not too much for you .

[RyanJ]

You should write a book - you explain it better than my book does

 

I understand it much better now and with some practice (And some more help from my teacher too ) I should be able to get this right Maybe I'll try those excercises in the book too... Does this get easier with practice?

 

Thanks for your help (I'll read this a few more times so I'm shure I understand what you wrote).

 

Ryan Jones

[vrus]

I was in need of much of the same information. Thnx to both of you.

[jdurg]

The stuff is really 'complexly simple'. At first it seems utterly complex. Then you learn about it and it seems really simple. Then you learn more and it becomes utterly complex again. It's really remarkable.

[RyanJ]

The stuff is really 'complexly simple'. At first it seems utterly complex. Then you learn about it and it seems really simple. Then you learn more and it becomes utterly complex again. It's really remarkable.

 

Oh... its one of those

 

I'll just have to work extra hard to make shure I get it right then

 

I have one more question what do the f and g orbitals look like?

 

Cheers,

 

Ryan Jones

[jdurg]

The f and g orbitals are complex shapes that really can't be described. I think if you look on webelements you may be able to find representations of them, but they certainly don't look like typical shapes.

[RyanJ]

The f and g orbitals are complex shapes that really can't be described. I think if you look on webelements you may be able to find representations of them, but they certainly don't look like typical shapes.

 

Ok, thanks jdurg

 

Cheers,

 

Ryan Jones