Chemical Formula Element Order

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Nell Mitchell 1E
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Joined: Fri Sep 28, 2018 12:16 am

Chemical Formula Element Order

Postby Nell Mitchell 1E » Sun Oct 07, 2018 8:48 pm

Is there a rule of thumb for the order elements should be listed in formula? For example in problem F.17, how do you know that Osmium should be listed first?

Chem_Mod
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Re: Chemical Formula Element Order

Postby Chem_Mod » Sun Oct 07, 2018 9:16 pm

Hill notation is used to determine which atom to list first in a chemical equation, but I would not worry too much about this.

Louis Zhao 4C
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Joined: Sun Oct 07, 2018 12:17 am

Re: Chemical Formula Element Order

Postby Louis Zhao 4C » Sun Oct 07, 2018 9:18 pm

I think the general consensus is that the atoms with lower electronegativity values are written first. So Osmium has the lowest electronegativity of 2.0, compared to Carbon (2.6) and Oxygen(3.4) so it would make sense to write it first. However, I don't think the order of elements in a chemical formula is too important.

Chem_Mod
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Re: Chemical Formula Element Order

Postby Chem_Mod » Sun Oct 07, 2018 9:29 pm

Using the rule of electronegativity doesn't quite work, eg. CH4, but like you said, it isn't so critical to know this for now. You will get used to writing chemical equations as the quarter progresses.

Mallory_Podosin_1H
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Joined: Fri Sep 28, 2018 12:15 am

Re: Chemical Formula Element Order

Postby Mallory_Podosin_1H » Wed Oct 10, 2018 9:12 pm

I had this same question... I think that for now it doesn't matter but later on it may start to matter/we will get used to the order in which the elements are listed.

Dayna Pham 1I
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Re: Chemical Formula Element Order

Postby Dayna Pham 1I » Wed Oct 10, 2018 9:25 pm

Hello!

I asked Dr. Lavelle this question today in office hours, and he said for now, not to worry about it. Conventionally, for organic molecules, it usually goes in the order of C H O, but if it has lesser known elements, like Cl or Br, it can be in any order.

Some order the elements in descending order with regards to the number of atoms each has, but it shouldn't be a big worry for now I think.

Hope this helped!


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