[sabre2th1]

Why does the P atom have more than eight electrons in its outer shell?

[EierVonSatan]

It has ''expanded it's octet'' which means it is using a d orbital to bond 10 electrons instead of just s and p orbitals to bond only 8

[otrivine]

(Original post by EierVonSatan)
It has ''expanded it's octet'' which means it is using a d orbital to bond 10 electrons instead of just s and p orbitals to bond only 8

in an exam how would we now if this applies the octet rule?

[lukas1051]

(Original post by otrivine)
in an exam how would we now if this applies the octet rule?

I highly doubt they'd expect you to know something like this in an exam. I don't know if you're doing GCSE or A-level, but either way, any dot and cross questions will be ordinary, simple covalent molecules with each atom having the expected number of bonds/electrons. Sometimes chemistry just doesn't like to obey rules, but it's unfair to expect you to know things like this (I'm doing A2 level chemistry and I wouldn't know how to do this). I mean I suppose you could deduce it from the fact that chlorine always(?) donates one electron so it's the only possible structure but I personally wouldn't worry about it. This is pretty helpful: http://sixthsense.osfc.ac.uk/chemist...g/covalent.asp

[amd1]

(Original post by otrivine)
in an exam how would we now if this applies the octet rule?

Well in this particular example you can see that it can't possibly bond to 5 Cls without having more than 8 electrons in its outer shell, simply because it already has 5 valence electrons, and so only needs 3 more to reach 8. After some practise you get quite used to 'knowing' which compounds use the d orbitals and which don't-if not, just learn them!

[sabre2th1]

(Original post by lukas1051)
I highly doubt they'd expect you to know something like this in an exam. I don't know if you're doing GCSE or A-level, but either way, any dot and cross questions will be ordinary, simple covalent molecules with each atom having the expected number of bonds/electrons. Sometimes chemistry just doesn't like to obey rules, but it's unfair to expect you to know things like this (I'm doing A2 level chemistry and I wouldn't know how to do this). I mean I suppose you could deduce it from the fact that chlorine always(?) donates one electron so it's the only possible structure but I personally wouldn't worry about it. This is pretty helpful: http://sixthsense.osfc.ac.uk/chemist...g/covalent.asp

(Original post by amd1)
Well in this particular example you can see that it can't possibly bond to 5 Cls without having more than 8 electrons in its outer shell, simply because it already has 5 valence electrons, and so only needs 3 more to reach 8. After some practise you get quite used to 'knowing' which compounds use the d orbitals and which don't-if not, just learn them!

For the Edexcel AS specification, I know that you have to be able to draw the shape of the PCl5 molecule, but am I expected to apply this "expand it's octet" idea and draw the dot and cross?

(Original post by EierVonSatan)
It has ''expanded it's octet'' which means it is using a d orbital to bond 10 electrons instead of just s and p orbitals to bond only 8

[lukas1051]

(Original post by sabre2th1)
For the Edexcel AS specification, I know that you have to be able to draw the shape of the PCl5 molecule, but am I expected to apply this "expand it's octet" idea and draw the dot and cross?

I highly doubt it. Dot and cross diagrams, and molecule shapes are two different areas, although you'll probably encounter both I highly doubt dot and cross will be applied to more complex molecules such as PCl5 or SF6.

[EierVonSatan]

(Original post by lukas1051)
I highly doubt it. Dot and cross diagrams, and molecule shapes are two different areas, although you'll probably encounter both I highly doubt dot and cross will be applied to more complex molecules such as PCl5 or SF6.

It would be very mean to ask something like:

''Draw a dot and cross diagram for the Re₂Cl₈^2- ion''

[thegodofgod]

(Original post by EierVonSatan)


It would be very mean to ask something like:

''Draw a dot and cross diagram for the Re₂Cl₈^2- ion''

In one AQA paper they asked for the Lewis-dot structure of SO₄^2-, and about the delocalisation as well

[cpchem]

(Original post by lukas1051)
I highly doubt they'd expect you to know something like this in an exam. I don't know if you're doing GCSE or A-level, but either way, any dot and cross questions will be ordinary, simple covalent molecules with each atom having the expected number of bonds/electrons. Sometimes chemistry just doesn't like to obey rules, but it's unfair to expect you to know things like this (I'm doing A2 level chemistry and I wouldn't know how to do this). I mean I suppose you could deduce it from the fact that chlorine always(?) donates one electron so it's the only possible structure but I personally wouldn't worry about it. This is pretty helpful: http://sixthsense.osfc.ac.uk/chemist...g/covalent.asp

Chemistry obeys the rules... it's just that you don't know all of the rules yet.

Oh, and by the way, every now and again we have to rewrite the rules.

[illusionz]

(Original post by cpchem)
Chemistry obeys the rules... it's just that you don't know all of the rules yet.

Oh, and by the way, every now and again we have to rewrite the rules.

Was just about to say the exact same thing

[amd1]

(Original post by sabre2th1)
For the Edexcel AS specification, I know that you have to be able to draw the shape of the PCl5 molecule, but am I expected to apply this "expand it's octet" idea and draw the dot and cross?

I'm doing higher level IB, so have had to learn a hell of a lot of weird shapes/structures! But it's not the type of thing they should expect in detail at AS, because even our standard level chemists don't learn about it. Just make sure you know exactly which molecules you need to learn and have a basic understanding of how it works, then hopefully you'd be able to apply it to other molecules (if they were nasty enough to diverge off the syllabus).