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# Starting a foundation degree after 10 years away from study.....P. table confusion! watch

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1. Hey guys,
I am doing a foundation degree after 10 years away from study, unbelievably, I have forgotten everything. I thought going over some old text books would help bring it all back to me but it hasn't and now i'm worried.

So in the periodic table, the horizontal rows are grouped into periods, 1 - 7, so each of these horizontal rows indicates how many shells each atom has , or so my texbook tells me.

But lets take mercury for instance, it has 80 electrons, it is in period 6, so therefore going by this theory it should have 6 shells, it however has 11 shells, 2 in the first shell followed by 9 shells of 8 electrons and finally one last shell of 6 electrons.

The virtical rows are groups, or so my textbook tells me and this indicates how many electrons are in the outer shell of an atom. This is fine for boron, its in group 3, and in period 2. So it does indeed have two shells as it is in period two and it is in group 3 which means it has 3 electrons in its outer shell, yes it does. However, when I look at arsenic "AS", it is in group 5 which would indicate it has 5 electrons in its outer shell, it is also in period 4 which would indicate it has 4 outer shells, however it has 5 outer shells! It is in group 5 which would indicate it has 5 electrons in its outer shell, but it doesn't, it has 7.

I thought I has a good grasp on the periodic table yesterday, but after looking into it more today, i am so confused and back to square on!

all help is appreciated.
2. Your understanding of shells is at GCSE standard. Is there a chapter on orbitals in that book? S, P and E orbitals?

In essence, each 'shell' you described can be broken down into smaller energy levels and this is where your confusion is coming from.
3. (Original post by hurricaneee)
x
As Occam's Chainsaw hinted at, the idea that a shell can only contain 8 electrons only works for the early atoms, up to calcium. Once you reach the transition metals, further subshells are occupied, which mean that a ground state atom's higher-energy shells can contain 18 or even 32 electrons. You might find this page on chemguide handy for a quick summary.
4. Hey mate,
No there isn't anything on S, P and e oribitals, do you have any links or recommend any youtube videos/books?
5. (Original post by hurricaneee)
Hey mate,
No there isn't anything on S, P and e oribitals, do you have any links or recommend any youtube videos/books?
BJack gave you a link to chemguide which, in my experience, is great. WJEC do free revision aids on their website too which definitely have this in them.

6. (Original post by hurricaneee)
Hey mate,
No there isn't anything on S, P and e oribitals, do you have any links or recommend any youtube videos/books?
(For what it's worth, they're d orbitals, not e orbitals.)
7. (Original post by BJack)
(For what it's worth, they're d orbitals, not e orbitals.)
I mistyped. Sorry about that. E is right above D on the keyboard
8. Thanks very much for the replies guys, it makes much more sense now.

I missed the first few weeks of term sadly and they went over the basics and a run through of GCSE chemistry for background etc.

My first class was on friday past and it all went over my head, sadly the teacher didn't seem to worried about helping those out who were struggling.

The lesson was on relative atomic mass, relative isotopic mass and relative molecular mass in terms of carbon-12. Calculating the number of moles etc.

Anyone recommend a good base to start here? Any reading I am doing isn't getting it threw to me at all.
9. (Original post by hurricaneee)
Anyone recommend a good base to start here? Any reading I am doing isn't getting it threw to me at all.
Reading is too passive. You need to get a problem book and do some questions. Do you know what exam board you are on.
10. I sadly do not buddy, the more I look at this topic on the internet the more it scares me. However, I know if I hadn't missed the first two weeks of class I would be fine.

Can you reccomend a workbook?

thanks very much!

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Updated: October 6, 2013
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