# The 3rd shell holds 8 or 18 electrons.

Watch
Announcements
#1
Hey I am a bit confused here. I've just looked into the AS book I bought to see what kind of stuff I will study from September on.

I found one weird thing. I know from GCSE that the first shell occupies 2 electrons the 2nd 8 and the 3rd 8 aswell.

This AS book states that the 3rd shell occupies 18 electrons. . It further goes on to describe s,p,d and f sub shells and their orbitals.

Why is there this contradiction, what am I missing .
0
9 years ago
#2
Things are simplified at GCSE. At A-level you learn the real facts - shells can hold 2, 8, 18 and 32 electrons respectively.
0
9 years ago
#3
(Original post by Giggy88)
Hey I am a bit confused here. I've just looked into the AS book I bought to see what kind of stuff I will study from September on.

I found one weird thing. I know from GCSE that the first shell occupies 2 electrons the 2nd 8 and the 3rd 8 aswell.

This AS book states that the 3rd shell occupies 18 electrons. . It further goes on to describe s,p,d and f sub shells and their orbitals.

Why is there this contradiction, what am I missing .
GCSE teaches 8 because it doesn't take into account 10 of the electrons (its a bit wtfish I know)

Basically, there are 18 because each shell is divided into s, p and d sub-shells. s always holds 2, p always holds 6 and d always holds 6 (there's an f shell that holds 14, it goes up in 4's xD)

Basically, shell 3, when full, looks like this:

1s2, 2s2, 2p6, 3s2, 3p6, 3d10

There are 2 on the 1st shell, 2+6=8 on the 2nd shell, and 2+6+10=18 on the 3rd shell
0
9 years ago
#4
18.

Period 3 elements only go up to 8 for the 3rd shell, this is as far as you learn for GCSE generally.

When you get to transition metals the 4th shell stays at 1 or 2 electrons and the third shell changes.

I can't explain the orbitals well though.
1
#5
(Original post by Jake200493)
GCSE teaches 8 because it doesn't take into account 10 of the electrons (its a bit wtfish I know)

Basically, there are 18 because each shell is divided into s, p and d sub-shells. s always holds 2, p always holds 6 and d always holds 6 (there's an f shell that holds 14, it goes up in 4's xD)

Basically, shell 3, when full, looks like this:

1s2, 2s2, 2p6, 3s2, 3p6, 3d10

There are 2 on the 1st shell, 2+6=8 on the 2nd shell, and 2+6+10=18 on the 3rd shell
Ok, this makes a bit more sense (after reading twice ).. I can follow your electron configuration for shell 3.

But the reason they only tell us 8 of the electrons occupying the 3rd shell and not 18 is still not clear. (This assumes that they have left out the 10 electrons in the 3d orbital.) For Simplicity? Well, I hope there is a more profound reason.

Can't believe I always used to write e.g electron configuration of calcium 2,8,8,2. After looking closely it actually relates to the electron config. shown at AS e.g 1s2, 2s2, 2p6, 3s2, 3p6 4s2. The 2 stands for the 1s2. The 8 stands for the 2s2 and 2p6. And the third 8 stands for 3s2 and 3p6. And lastly the 2 standing for 4s2. (Hope its clear what I am babbling about. )
1
9 years ago
#6
This is why you should wait.
You just majorly screwed with your chemistry confidence there, m'friend. Bonne chance if you decide to continue though!
3
9 years ago
#7
(Original post by Giggy88)
Ok, this makes a bit more sense (after reading twice ).. I can follow your electron configuration for shell 3.

But the reason they only tell us 8 of the electrons occupying the 3rd shell and not 18 is still not clear. (This assumes that they have left out the 10 electrons in the 3d orbital.) For Simplicity? Well, I hope there is a more profound reason.
Its because it gets more complicated when you start using the d shell, due to the 4s sub-shell. (I'll explain, but its A2 work xD)

Basically, in the transition metals, it gets a bit weird. The 4s sub-shell has a lower energy than the 3d shells, so they fill up first. And the configuration for the transition metals is as follows:

• Sc = 1s2,2s2,2p6,3s2,3p6,3d1,4s2
• Ti = 1s2,2s2,2p6,3s2,3p6,3d2,4s2
• V = 1s2,2s2,2p6,3s2,3p6,3d3,4s2
• Cr = 1s2,2s2,2p6,3s2,3p6,3d5,4s1
• Mn = 1s2,2s2,2p6,3s2,3p6,3d5,4s2
• Fe = 1s2,2s2,2p6,3s2,3p6,3d6,4s2
• Co = 1s2,2s2,2p6,3s2,3p6,3d7,4s2
• Ni = 1s2,2s2,2p6,3s2,3p6,3d8,4s2
• Cu = 1s2,2s2,2p6,3s2,3p6,3d10,4s1
• Zn = 1s2,2s2,2p6,3s2,3p6,3d10,4s2

As you can see, Cr and Cu don't really follow that pattern, and an energy from their 4s sub-shell gets promoted to the 3d shell. Its like this a bit for Cu:

>> >> >> >> >> 3d
> 4s
>> >> >> 3p
>> 3s
>> >> >> 2p
>> 2s
>> 1s

Which explains the lack of 3d4 and 3d9 in the list

If any of that makes any sense I'm not too great at explaining xD
1
#8
(Original post by george..)
18.

Period 3 elements only go up to 8 for the 3rd shell, this is as far as you learn for GCSE generally.

When you get to transition metals the 4th shell stays at 1 or 2 electrons and the third shell changes.

I can't explain the orbitals well though.
So you are saying the electrons occupy the 3rd shell upto 8 electrons (3s2, 3p6) and then continue with the 4th shell for 2 electrons and if there are still more electrons depending on the element they come back to the 3rd shell filling the d orbital?
0
9 years ago
#9
(Original post by Giggy88)
Hey I am a bit confused here. I've just looked into the AS book I bought to see what kind of stuff I will study from September on.

I found one weird thing. I know from GCSE that the first shell occupies 2 electrons the 2nd 8 and the 3rd 8 aswell.

This AS book states that the 3rd shell occupies 18 electrons. . It further goes on to describe s,p,d and f sub shells and their orbitals.

Why is there this contradiction, what am I missing .
it is contradictory yes, but gcse is simplified...

it can hold more than 8 because of the different orbitals
0
#10
(Original post by Jake200493)
Its because it gets more complicated when you start using the d shell, due to the 4s sub-shell. (I'll explain, but its A2 work xD)

Basically, in the transition metals, it gets a bit weird. The 4s sub-shell has a lower energy than the 3d shells, so they fill up first. And the configuration for the transition metals is as follows:

• Sc = 1s2,2s2,2p6,3s2,3p6,3d1,4s2
• Ti = 1s2,2s2,2p6,3s2,3p6,3d2,4s2
• V = 1s2,2s2,2p6,3s2,3p6,3d3,4s2
• Cr = 1s2,2s2,2p6,3s2,3p6,3d5,4s1
• Mn = 1s2,2s2,2p6,3s2,3p6,3d5,4s2
• Fe = 1s2,2s2,2p6,3s2,3p6,3d6,4s2
• Co = 1s2,2s2,2p6,3s2,3p6,3d7,4s2
• Ni = 1s2,2s2,2p6,3s2,3p6,3d8,4s2
• Cu = 1s2,2s2,2p6,3s2,3p6,3d10,4s1
• Zn = 1s2,2s2,2p6,3s2,3p6,3d10,4s2

As you can see, Cr and Cu don't really follow that pattern, and an energy from their 4s sub-shell gets promoted to the 3d shell. Its like this a bit for Cu:

>> >> >> >> >> 3d
> 4s
>> >> >> 3p
>> 3s
>> >> >> 2p
>> 2s
>> 1s

Which explains the lack of 3d4 and 3d9 in the list

If any of that makes any sense I'm not too great at explaining xD
Well I think I understand . Well here is what I picked up, correct me if wrong.

Due to different energy levels i.e. 3d orbitals having more energy than 4s orbitals, the 4s orbitals are filled first? So its right to assume that if there are more electrons left after filling the 4s orbital with 2 electrons, you go back to 3d orbital and fill it with 10 electrons (if available).

But this can only be seen at the transition metals simply because you do not reach such a high number of electrons before the transition metals, i.e. in period 1,2 and 3?

So at GCSE they just didn't mention the 3d orbital because if they do mention 18 electrons, they would have to explain the whole idea of 3d having more energy and being occupied later than 4s?
2
9 years ago
#11
(Original post by Giggy88)
Well I think I understand . Well here is what I picked up, correct me if wrong.

Due to different energy levels i.e. 3d orbitals having more energy than 4s orbitals, the 4s orbitals are filled first? So its right to assume that if there are more electrons left after filling the 4s orbital with 2 electrons, you go back to 3d orbital and fill it with 10 electrons (if available).

But this can only be seen at the transition metals simply because you do not reach such a high number of electrons before the transition metals, i.e. in period 1,2 and 3?

So at GCSE they just didn't mention the 3d orbital because if they do mention 18 electrons, they would have to explain the whole idea of 3d having more energy and being occupied later than 4s?
YES! That's exactly right WOOOOOOOOOOOO I explained something without causing mass confusion :') I can mark that off my "What I need to be able to do to teach" list :')

If you need any Chem help while you're doing your A-Levels, you can always inbox me because I'm doing it at Uni (hopefully) xD And its helped me revise transition metals for my exam tomorrow Thanks xD
0
#12
(Original post by Jake200493)
YES! That's exactly right WOOOOOOOOOOOO I explained something without causing mass confusion :') I can mark that off my "What I need to be able to do to teach" list :')

If you need any Chem help while you're doing your A-Levels, you can always inbox me because I'm doing it at Uni (hopefully) xD And its helped me revise transition metals for my exam tomorrow Thanks xD
LooL yep, you definitely can tick that off . Thanks a lot, that's nice of you. I will inbox you if anything is unclear. I was also thinking of doing it at Uni! (Despite doing 4 AS its the only one I am so curious about that I start reading about it already in the summer. xD) Well lets see how A level goes first.

Good luck with your exam tomorrow !
0
9 years ago
#13
(Original post by Giggy88)
LooL yep, you definitely can tick that off . Thanks a lot, that's nice of you. I will inbox you if anything is unclear. I was also thinking of doing it at Uni! (Despite doing 4 AS its the only one I am so curious about that I start reading about it already in the summer. xD) Well lets see how A level goes first.

Good luck with your exam tomorrow !
No problem And thanks xD Hopefully it'll go well, I'm gonna cram like hell tomorrow :')
0
7 years ago
#14
(Original post by Jake200493)
GCSE teaches 8 because it doesn't take into account 10 of the electrons (its a bit wtfish I know)

Basically, there are 18 because each shell is divided into s, p and d sub-shells. s always holds 2, p always holds 6 and d always holds 6 (there's an f shell that holds 14, it goes up in 4's xD)

Basically, shell 3, when full, looks like this:

1s2, 2s2, 2p6, 3s2, 3p6, 3d10

There are 2 on the 1st shell, 2+6=8 on the 2nd shell, and 2+6+10=18 on the 3rd shell
Then why is Argon considered as a noble gas with a full outer shell? Because the third shell holds 18 right? Argon only has 8 in the third level. This is really getting in the way of my AS Chemistry
0
7 years ago
#15
(Original post by Douve)
Then why is Argon considered as a noble gas with a full outer shell? Because the third shell holds 18 right? Argon only has 8 in the third level. This is really getting in the way of my AS Chemistry
Because when you consider the orbitals energetically, the next orbital on shell 3 (d) is MUCH higher in energy. So much higher that it's easier to put electrons in 4s first.

Noble gases are stable because they have the highest nuclear charge (number of protons) for a given shell (or period), their outermost electrons are strongly attracted to the nucleus and there is no space in the outer orbital for bonding electrons to fit.

In order to bond to a nobel gas, you'd have to promote electrons to a MUCH higher shell which is energetically unstable and very hard to do (impossible for He, Ne).

It's not the "full shell" itself that results in it being stable, it's what that means as far as the electrons, the nuclear charge, and the ability to put more electrons into the shell.

Also- way to go digging up a 2 year old thread.....
0
3 years ago
#16
Can someone please explain what the issue is with 'digging up old threads' when, unless the laws of science have changed, it is just as relavent today? I get knocked every time I revive an old thread. It's like, "well the whole world learned that ten years ago, so where the hell were you?" "Er... playing hopscotch."
0
3 years ago
#17
(Original post by Iron_Maiden)
Can someone please explain what the issue is with 'digging up old threads' when, unless the laws of science have changed, it is just as relavent today? I get knocked every time I revive an old thread. It's like, "well the whole world learned that ten years ago, so where the hell were you?" "Er... playing hopscotch."
Thank you for reviving this though, i learnt something from this thread
and i am shook
0
3 years ago
#18
Can someone please explain what the issue is with 'digging up old threads' when, unless the laws of science have changed, it is just as relavent today?I get knocked every time I revive an old thread. It's like,
0
3 years ago
#19
(Original post by Iron_Maiden)
Can someone please explain what the issue is with 'digging up old threads' when, unless the laws of science have changed, it is just as relavent today? I get knocked every time I revive an old thread. It's like, "well the whole world learned that ten years ago, so where the hell were you?" "Er... playing hopscotch."
Most people dig up old threads and seemingly ask people, who probably haven't been on TSR for years, questions that they aren't going to get answers to.

Why not just post a thread of your own? Maybe you might find an old thread and want clarification on something, but I would suggest avoiding quoting. Like you didn't here. I would go with, "I have found this old thread and there is something discussed here that I don't get..."

But in this here case, you have dug up a thread and added your question in a completely non-related way. This should definitely have been done in your own thread. And possibly not even in the chemistry section.

But, I am no mod. What do I know?
1
3 years ago
#20
But if you start a new thread instead of digging up old ones, you get accused of asking things that have been asked before and are pointed towards the search bar.
0
X

new posts
Back
to top
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### Poll

Join the discussion

Yes (86)
72.27%
No (33)
27.73%