Diamond & Silicon oxide

Evidence 1- if you look at the structure you will see that each Si atom is in a tetrahedral orientation with respect to the oxygen atoms showing the bonding to be sp3 hybridised. i.e. no pi bonds

Evidence 2- if oxygen were to form a double bond with one of the silicon atoms it would have to form three bonds in total - it cannot do this

Evidence 3 - the Si-O-Si bond angle suggests sp3 hybridisation of the oxygen electrons i.e. no pi bonds.

Evidence 4 - SiO2 does not conduct electricity therefore it cannot have conjugated pi bonds.

There are no weak intramolecular forces for the simple reason that they are all covalent bonds. It's a giant molecule.

Did you have a look at the structure on the link I sent?

Silicon DOES NOT form pi bonds in silicon dioxide.

It does not have weak bonds it has strong bonds (just a little less strong than carbon in diamond) - all the bonding is covalent sigma, direct orbital overlap.

Perhaps you are getting confused with silicates???

These have the SiO4(2-) ion - but they are not silicon dioxide.

Your logic is flawed.

What makes you think that carbon has to be atomised to boil? why can't it vaporise as C2 or C4 or buckyballs or nanotubes or one of the other myriad forms of carbon?

Hellooo?

Um Im not quite getting it?

YES!!!!!!!!!!!!! Oops sorry...are u totally sure? coz thats my theory too...

With the longer silicon-oxygen bonds, the p orbitals on the silicon and the oxygen aren't quite close enough together to allow enough sideways overlap to give a stable pi bond.

Marcus

Er - there are no pi bonds in silicon oxide. There aren't any delocalised electrons. All the electrons are held tightly between the atoms, and aren't free to move, as opposed to carbon dioxide. With the longer silicon-oxygen bonds, the p orbitals on the silicon and the oxygen aren't quite close enough together to allow enough sideways overlap to give a stable pi bond. Carbon is the only Group 4 element that forms double bonds (pi) with oxygen.

Marcus
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I can tell you for certain that is incorrect.

Marcus

this is true, but in buckyballs etc there have to be quite specific comditions for them to form, otherwise they would have been noticed a lot earlier. if it is a vapour it wont be in very large clumps and so it stands to reson that some of the bonds are likely to have to be broken whereas SiO2 can exist as a single molecule where no net bondiong change is noticed.

large clumps of carbon would not be a gas either, so they will be in small bits at the very least even if only c2 or c4 you still ahve to break some bonds, unless they miraculously cyclise.

the whole point is that carbon does not really boil at all as it has no liquid phase at 1 bar. it cant vapourise as any of the oher allotropes of carbon as (excluding fullerenes) they are all in the solid state.