Any help with electron shells and orbitals?

Ok I have a science test tomorrow and I'm having trouble with electron orbitals and shells. I kind of know what they are but I need an actual definition. I can't find any anywhere. And, what are the levels of the shells. I know the first few, I think it's 2-8-8 but then I don't know. Any help?

Any help with electron shells and orbitals?
1s2 ( 2 electrons)



2s2 , 2p6 ( 8 electrons)



3s2 , 3p6 , 3d10 ( 18 electrons)
Reply:it is a very simple concept. it is nothing but 2n^2

if n = 1, then s orbital shell is 2*1*1 = 2

if n = 2, then p orbital shell is 2*2*2 = 8

if n = 3, then d orbital shell is 2*3*3 =18

if n = 4, then f orbital shell is 2*4*4 = 32

and so on

for eg the atomic number of chlorine is 17 and the respective shells are in the order of 2,8,7.

the last shell constitutes the balance electron.

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