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Noah Carey 1G
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Joined: Fri Apr 06, 2018 11:02 am
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Postby Noah Carey 1G » Fri Apr 06, 2018 5:25 pm

In exercise H.3, why is it written SiH4 instead of H4Si? I read that Carbon and Hydrogen come before the other atoms and then the rest follow in alphabetic order (Hill System). Is this an exception or am I just confused?

Marina Souliman 1K
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Joined: Fri Apr 06, 2018 11:05 am

Re: H.3

Postby Marina Souliman 1K » Fri Apr 06, 2018 9:38 pm

I think this might be an exception but I'm not 100% sure. I looked it up and found that Silane is interchangeable between SiH4 and H4Si but I couldn't find an exact explanation why it can be written both ways. Interesting question, though. I didn't know it was possible.

Here's the link I found. Hope this helps.
https://pubchem.ncbi.nlm.nih.gov/compou ... ection=Top

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Re: H.3

Postby KristinaNguyen_1A » Sat Apr 07, 2018 10:07 am

I agree that through the Hill System, H4 should go before Si, but I think it is disregarded because in either order it will not affect the balancing process, there will still be 4 H and 1Si in SiH4 and H4Si.

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Joined: Wed Nov 15, 2017 3:01 am

Re: H.3

Postby ElizabethP1L » Sat Apr 07, 2018 12:31 pm

Hi, Noah! I actually don't know much about the Hill System, unfortunately. In my own case, I intuitively knew the H4 would follow the Si.
However, usually when the H comes first, it usually means its an acid:
H2CO3 (carbonic acid)
HNO3 (nitric acid)
HClO4 (perchloric acid) etc....

Therefore, if it was written H4Si we'd probably expect it to be an acid and we have not touched upon acid-base reactions yet. Another clue as to why Si would come first is from the structure shown in the picture of H.3. You'll notice that Si is the center atom and the four hydrogens flank either side. This is also a clue that Si should precede the hydrogens. However, you could still balance the chemical equation just fine and I doubt you'd be penalized for writing it as H4Si. Hope this helped! :)

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