Balancing Equations: Oxygen in Compounds

[J-Girl]

hi there,:) I am just wondering, when balancing equations, because oxygen is a diatomic molecule, when it is in a compound, can it exist in threes of fives? for example, Fe2O3, or does it have to be 2Fe203. Or is it just when it is a single molecule of oxygen(and not in a compound) that it must be in atoms of two? So my question is, when oxygen in is a compound, does it have to exist in atoms of twos, or can it be uneven? sorry this may be a stupid question but its not clear in my textbook! ! thanksssss:D

 

[Borek]

It is diatomic only when in the form of oxygen molecules. Same can be said about all other diatomic gases. When in compounds, they don't have to be in pairs - so CaO contains one oxygen atom, CO₂ two, Fe₂O₃ three, OsO₄ four and so on.

Note that gaseous oxygen - while in most cases diatomic - has also a triatomic form, called ozone. You will not see it often in reactions when starting to learn chemistry, but it is quite an important compound.

 

[J-Girl]

but what about H20, isn't it always written as 2H20? or just H20?

 

[Borek]

H₂O - single water molecule - is perfectly correct.

NaOH + HCl -> NaCl + H₂O

 

[Dr_Morbius]

Didn't your chemistry teacher explain this?

 

[J-Girl]

shes wasnt very direct. so diatomic atoms are only covalently bonded when they exist naturally, before they enter into chemical reactions? this was the one thing that wasnt clear to me in chem class

 

[Borek]

so diatomic atoms are only covalently bonded when they exist naturally, before they enter into chemical reactions?

Diatomic molecules. It can be put that way, although atoms of the same element can be also covalently bonded in the compound. They don't have to, but it happens, so your statement (especially "only") is way too strong.

Some gases in free, elemental form, are present as diatomic molecules.

 

[J-Girl]

ohh haha sorry i did mean diatomic molecules:)my bad.

 

[Dr_Morbius]

If you don't understand something raise your hand and ask the teacher. Don't be shy. And keep asking until the teacher explains it to your satisfaction. That's their job.

In high school my chemistry teacher knew less chemistry than I did and I had to correct him a few times.