Chemical Reactions: Why we Use Symbols with Numbers

[intenzxboi]

I was wondering how come when ever there's a question like aluminum reacts with bromine it is usually written like Al + Br2? or Potassium reacts with oxygen is K + O2?

How do we know when there's 2 of them?? Is there like a special rule? Why isn't there K2 or Al2??

 

[pr0blumz]

I was wondering how come when ever there's a question like aluminum reacts with bromine it is usually written like Al + Br2? or Potassium reacts with oxygen is K + O2?

How do we know when there's 2 of them?? Is there like a special rule? Why isn't there K2 or Al2??

Those are not chemical equations. AlBr3 & K2O2 are though. Al forms +3 ions so you would need three -1 bromide ions to balance the charge.

 

[w3390]

http://en.wikipedia.org/wiki/Diatomic_molecule

 

[Borek]

Those are not chemical equations.

They were not inteded to be 'equations'.

AlBr3 & K2O2 are though.

No - these are 'formulas'.