Shell numbers/orbitals and Periods Watch

tingirl
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I was doing a bit of chemistry revision and now I've got myself all confused about how shell numbers are related to periods of the periodic table...

Basically, do all elements in the same period have the same number of shells?
If so, why are there 4s orbitals and 3d orbitals both in the fourth period (surely the 3 in "3d" means that the 3d subshell is part of the 3rd shell, right? So why are they in period 4?)

Shells are groups of orbitals which are a similar distance from the nucleus. So why is the 3d subshell part of the 3rd shell and not part of the 4th shell?

I don't know if I'm just tired or something but none of this is making sense, so I'd be SOOO grateful if someone could help me understand the above!!!!
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ThatPerson
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(Original post by tingirl)
I was doing a bit of chemistry revision and now I've got myself all confused about how shell numbers are related to periods of the periodic table...

Basically, do all elements in the same period have the same number of shells?
If so, why are there 4s orbitals and 3d orbitals both in the fourth period (surely the 3 in "3d" means that the 3d subshell is part of the 3rd shell, right? So why are they in period 4?)

Shells are groups of orbitals which are a similar distance from the nucleus. So why is the 3d subshell part of the 3rd shell and not part of the 4th shell?

I don't know if I'm just tired or something but none of this is making sense, so I'd be SOOO grateful if someone could help me understand the above!!!!
I think I understand your question.

Basically, when both shells are empty, the 4s subshell has a lower energy level than the 3d subshell.

Once electrons fill these shells they flip round to the expected order (3d then 4s).
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charco
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(Original post by tingirl)
I was doing a bit of chemistry revision and now I've got myself all confused about how shell numbers are related to periods of the periodic table...

Basically, do all elements in the same period have the same number of shells?
If so, why are there 4s orbitals and 3d orbitals both in the fourth period (surely the 3 in "3d" means that the 3d subshell is part of the 3rd shell, right? So why are they in period 4?)

Shells are groups of orbitals which are a similar distance from the nucleus. So why is the 3d subshell part of the 3rd shell and not part of the 4th shell?

I don't know if I'm just tired or something but none of this is making sense, so I'd be SOOO grateful if someone could help me understand the above!!!!
The energy shells emerge from the solutions to the Schroedinger equation. 1, 2, 3, 4 etc

Each is sub-divided into sub-shells (except 1) and orbitals.

Energy level 1 has only 1 's' orbital (which can house 2 electrons)
Energy level 2 has 1 's' orbital and 3 'p' orbitals (which can house 8 electrons in total)
Energy level 3 has 1 's' orbital, 3 'p' orbitals and 5 'd' orbitals (which can house 18 electrons in total)
Energy level 4 has 1 's' orbital, 3 'p' orbitals, 5 'd' orbitals and 7 'f' orbitals (which can house 32 electrons in total)

BUT (and it's a big BUT) the actual energy of the orbitals in the shells means that the 4s orbital fills up before the 3d orbitals (Hundt's rule and the Aufbau principle).

Hence the 3d electrons are shown after the 4s electrons in the periodic table.

However, elements in the 3rd period have the empty 'd' orbitals available for extra bonding if needed. This is demonstrated in the hydrolysis of silicon tetrachloride or the octet expansion of phosphorus pentachloride etc.
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