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Structure and bonding

Hello, co2 and so2 both have double covalent bonds. However the answer states that silicon dioxide has single covalent bonds only, why ?

Thanks

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Reply 1
Avatar for alow
alow
19
What would a giant lattice of silicon dioxide look like?
Reply 2
Avatar for coconut64
coconut64
OP
16
Original post by alow
What would a giant lattice of silicon dioxide look like?


It's quite big; each s atom is bonded to 4 other o atoms.
Reply 3
Avatar for alow
alow
19
Original post by coconut64
It's quite big; each s atom is bonded to 4 other o atoms.


Exactly. That's your single bonds.
Reply 4
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coconut64
OP
16
Original post by alow
Exactly. That's your single bonds.


But if I am only looking at the dot and cross diagram, it suggests otherwise...
Reply 5
Avatar for alow
alow
19
Original post by coconut64
But if I am only looking at the dot and cross diagram, it suggests otherwise...


Silicon dioxide which isn't in a giant covalent structure, as far as I'm aware, isn't really a thing.
Reply 6
Avatar for coconut64
coconut64
OP
16
Original post by alow
Silicon dioxide which isn't in a giant covalent structure, as far as I'm aware, isn't really a thing.


https://www.google.co.uk/search?q=silicon+dioxide&espv=2&biw=1920&bih=912&source=lnms&tbm=isch&sa=X&sqi=2&ved=0ahUKEwjcnITKoefOAhXLD8AKHZ3RDeUQ_AUIBigB
The pic shows that it has a giant covalent structure. How do you know that it only has single covalent bond if you don't look at this?
Reply 7
Avatar for alow
alow
19
Original post by coconut64
https://www.google.co.uk/search?q=silicon+dioxide&espv=2&biw=1920&bih=912&source=lnms&tbm=isch&sa=X&sqi=2&ved=0ahUKEwjcnITKoefOAhXLD8AKHZ3RDeUQ_AUIBigB
The pic shows that it has a giant covalent structure. How do you know that it only has single covalent bond if you don't look at this?


Si is in the same group as carbon so has a valency of 4.
Reply 8
Avatar for coconut64
coconut64
OP
16
Original post by alow
Si is in the same group as carbon so has a valency of 4.


I understand that but the answer states that SO2 has single covalent bonds but co2 has double covalent bond, although they are the same in the dot and cross diagram. Why is that ? Thanks
Reply 9
Avatar for alow
alow
19
Original post by coconut64
I understand that but the answer states that SO2 has single covalent bonds but co2 has double covalent bond, although they are the same in the dot and cross diagram. Why is that ? Thanks


Si forming 4 Si-O bonds instead of two Si=O double bonds is due to the energy of it's 3p orbitals making this a more favorable situation.

The exact details of why this is are quite a bit beyond A Level, but I guess you could think of it as the Silicon orbitals which would form the pi bond not having enough "side-on" overlap with the singly sigma bonded oxygen's lone pairs to form a pi bond as these orbitals are quite a bit more diffuse than the orbitals of carbon. These orbitals however can form a sigma bond as they can have enough overlap "head-on" with the oxygen's orbitals.
(edited 7 years ago)
Reply 10
Avatar for coconut64
coconut64
OP
16
Original post by alow
Si forming 4 Si-O bonds instead of two Si=O double bonds is due to the energy of it's 3p orbitals making this a more favorable situation.

The exact details of why this is are quite a bit beyond A Level, but I guess you could think of it as the Silicon orbitals which would form the pi bond not having enough "side-on" overlap with the singly sigma bonded oxygen's lone pairs to form a pi bond as these orbitals are quite a bit more diffuse than the orbitals of carbon. These orbitals however can form a sigma bond as they can have enough overlap "head-on" with the oxygen's orbitals.


You're right, that's actually beyond my spec. It's strange because a question asking for a dot and cross diagram for so2 is just same as co2 but when asking for bonding, it's different. I will bear that in mind. Cheers!
Original post by coconut64
Hello, co2 and so2 both have double covalent bonds. However the answer states that silicon dioxide has single covalent bonds only, why ?

Thanks


Are you doing OCR? Because if you are, there is a tonne of mistakes in the book
Reply 12
Avatar for alow
alow
19
Original post by coconut64
You're right, that's actually beyond my spec. It's strange because a question asking for a dot and cross diagram for so2 is just same as co2 but when asking for bonding, it's different. I will bear that in mind. Cheers!


Yeah... I guess you could just do a dot and cross diagram of a silicon singly bonded to four oxygens? Strange question.
Reply 13
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coconut64
OP
16
Original post by Ze Witcher
Are you doing OCR? Because if you are, there is a tonne of mistakes in the book


Hi, yea I am doing that but the the dot and cross diagram for so2 I am sure is right cuz that's in one of the exam questions. It is just like co2 right?
Original post by coconut64
Hi, yea I am doing that but the the dot and cross diagram for so2 I am sure is right cuz that's in one of the exam questions. It is just like co2 right?


Hi, theoretically yes in terms of dot and cross but their bond angles differ
Original post by coconut64
Hi, yea I am doing that but the the dot and cross diagram for so2 I am sure is right cuz that's in one of the exam questions. It is just like co2 right?


No, in sulfur(IV) oxide there is a lone pair on the sulfur atom.
Reply 16
Avatar for alow
alow
19
Original post by Ze Witcher
Hi, theoretically yes in terms of dot and cross but their bond angles differ


Original post by charco
No, in sulfur(IV) oxide there is a lone pair on the sulfur atom.


Yeah... OP are you getting confused between SiO2 and SO2?
Original post by charco
No, in sulfur(IV) oxide there is a lone pair on the sulfur atom.


No one knew the oxidation number, in that case yes there is a lone pair on the sulfur atom, giving it a different bond angle
Reply 18
Avatar for alow
alow
19
Original post by Ze Witcher
No one knew the oxidation number, in that case yes there is a lone pair on the sulfur atom, giving it a different bond angle


In SO2, the sulfur clearly has an oxidation state of +4...
Original post by alow
In SO2, the sulfur clearly has an oxidation state of +4...


Hey, its been a few months since I've recapped this stuff :smile:

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