Writing Formula Order

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Will Pham 1J
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Joined: Wed Sep 30, 2020 10:00 pm

Writing Formula Order

Postby Will Pham 1J » Thu Oct 08, 2020 3:25 pm

Hi, I was wondering how we determine the order for the elements when writing out a formula. For example, if there is C, H, N, and O in a compound, which letters would come first and why.

Chem_Mod
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Re: Writing Formula Order

Postby Chem_Mod » Thu Oct 08, 2020 3:28 pm

For organic compounds, generally C and H come first and are followed by the other atoms in alphabetical order. For ionic compounds, the cation proceeds the anion.

Siwa Hwang 3G
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Re: Writing Formula Order

Postby Siwa Hwang 3G » Thu Oct 08, 2020 3:32 pm

When writing down empirical formulas, carbon always comes first, then hydrogen, then rest of the elements follow by alphabetical order.

Andre Fabian 1F
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Re: Writing Formula Order

Postby Andre Fabian 1F » Thu Oct 08, 2020 4:04 pm

According to this post https://chemistry.stackexchange.com/questions/1239/order-of-elements-in-a-formula, the Hill System is used when determining the order of chemical formulas. In short, carbon is always placed first, followed by hydrogen, and after those two the rest of the elements comprising the compound are sorted in alphabetical order.

Katie Phan 1K
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Re: Writing Formula Order

Postby Katie Phan 1K » Thu Oct 08, 2020 4:19 pm

Some exceptions to what the other's have stated would be in the case of ionic compounds in which the cation is listed first and then the anion, regardless of alphabetical order.

Katie Phan 1K
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Joined: Wed Sep 30, 2020 9:55 pm

Re: Writing Formula Order

Postby Katie Phan 1K » Thu Oct 08, 2020 4:21 pm

I forgot to mention in my previous post but I just realized that other exceptions would be things like oxides and acids. Acids usually begin with H and oxides end in O. Another example would be hydroxides since they end in OH.

David Y
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Re: Writing Formula Order

Postby David Y » Fri Oct 09, 2020 4:02 pm

I think it is Carbon first, the Hydrogen and the rest after.


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