Writing Formula Order

[Will Pham 1J]

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]

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]

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

[Andre Fabian 1F]

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]

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]

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]

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