[noob_]

Hello chem forums -
I understand the concept of this for the most of it, I guess it's just the conventions I don't get.
For example,
if i want to write the electronic configuration of Iron:
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^6

I use the following to write my subshell model:

Code: [Select]

http://media-2.web.britannica.com/eb-media/06/96906-004-FB4A8411.gifThis is example is also given in the textbook, along with my answer.
However, Underneath the answer it is written:
"it is customary to group the subshells of shells, so this is more usually written"
1s^2 2s^2 2p^6 3s^2 3p^6 3d^6 4s^2
So
A) would my answer be accepted as corrected in ALL situations?
B) using the book method, would i be correcting in writing for Bromine:
1s^2 2s^2 2p^6 3s^2 3p^6  3d^10 4s^2 4p^5?
Thanks, it's really just understanding which method i have to use!

OH AND 1 more thing!
Using the shell model -
I know that :
1st shell - max 2 electrons
2nd shell - max 8 electons
3rd shell - max 18 electrons
ETC
Why is it that, say when we write
Potassium it is written as 2,8,8,1 and not 2,8,9
And when we write Iron, it is written as 2,8,14,2
When clearly it could be written as 2,8,16
-I THINK I remember being told something about not exceeding 8 electrons per shell in most cases, however I can't be sure of this, at the moment I just cannot figure out why sometimes 8 electrons per shell is exceeded and sometimes it isn't when it can be...
Thanks, once again!

[cliverlong]

For me, chemguide,

http://www.chemguide.co.uk/atoms/properties/elstructs.html

is the model of clarity on such matters.

I think the section on period 4 is most relevant to your questions but read it from the beginning and make sure you understand all of it rather than glossing over and saying "yep, I know that already".

As to why the sub-shells fill as they do and why they contain what they do try:

http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch6/quantum.html

then

http://en.wikipedia.org/wiki/Quantum_number

for me, writing [Ar]3d³4s²  or [Ar]4s²3d³ for the electronic configuration of Vanadium is irrelevant as long as you get the number of electrons in the 3d and 4s orbitals correct. If you think about it, both forms give you the same information, there is no ambiguity, and one is just as easy to write as the other.

Clive

[cliverlong]

Taking your potassium example.

It has electronic configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹

We can write this in a more compact form, where we appear to lose some information by grouping the number of electrons in each orbit (1,2,3,4)

2.8.8.1

However, applying the rules about electron filling of orbitals using the rules for quantum numbers of electrons we can recreate the actual detailed orbital configuration from the more compact form

For your other questions, I suggest you study carefully the links I have provided in my earlier post.

Clive

[cliverlong]

Hello noob_ . What is you current view on writing out electronic configuration of elements?

[noob_]

thanks for the reply clive and i'm sorry i didnt get back to this right away.
I find no difficulty when writing out the electron config using the shell or subshell model except when with the shell model it gets to the point that an element with a shell which can hold more than 8 electrons (3rd)  and has fewer than 18 electrons in total is written out using more than the third shell. this is shown in the examples i listed above, and the same goes with elements which have more than 18 electrons... I'm sorry if i'm being confusing but what i mean to say is for eg:
Why do people write 2,8,8,1 when they can write 2,8,9. Isn't it the same thing? Or do people do this because of the subshell grouping?

[cliverlong]

thanks for the reply clive and i'm sorry i didnt get back to this right away.
I find no difficulty when writing out the electron config using the shell or subshell model except when with the shell model it gets to the point that an element with a shell which can hold more than 8 electrons (3rd)  and has fewer than 18 electrons in total is written out using more than the third shell. this is shown in the examples i listed above, and the same goes with elements which have more than 18 electrons... I'm sorry if i'm being confusing but what i mean to say is for eg:
Why do people write 2,8,8,1 when they can write 2,8,9. Isn't it the same thing? Or do people do this because of the subshell grouping?

Ok

I see where you are coming from

The answer is in the links I have given above but to address your particular example

The third "shell" , as you have written, has a capacity of 18 electrons, but the third shell isn't filled completely before 4s starts getting occupied by electrons. The reason for this order of filling is to do with energy levels of the orbitals. There is a good diagram of this in the chemguide link above

Taking the example 2.8.8.1 (Potassium)

as I wrote above, this is a more compact way of writing

1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹

It is only after 4s is fully occupied as 4s² are the 3d orbitals accessible to electrons, that's why there is that large "slab" of transitions metals starting in the 4th period.

So Scandium has the electronic configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹

I think (I'm not sure) we could write the electronic configuration of scandium in the compact form

2.8.9.2

where each orbit separated by a dot and each number just counts the electrons in an orbit and gives no information about orbital filling

[noob_]

thanks very much i understand this more than before!

[fcb]

Look up the Aufbau Principle.