Confused about subscripts and coefficients wrt forumulas

[instantresults]

What exactly is the difference between something like (XY)₂ and 2XY? I get that the 2XY would indicate 2 moles of XY, but I don't see why (XY)₂ wouldn't be the same thing, so long as the whole formula is surrounded by parenthesis? thanks for any help

 

[BvU]

Without context impossible to answer.

Example for (XY)₂ ? Standalone ? Or did you just make that up ?

 

[mjc123]

2XY means two moles of the species XY. (XY)₂ means one mole of the species (XY)₂, which contains two XY units bound together. for example, (CN)₂ is the molecule cyanogen. We could write it as C₂N₂, but writing it as (CN)₂ emphasises that it is made up of two CN groups joined together, as N≡C-C≡N, rather than any other arrangement of two C and two N atoms. 2CN would imply two separate CN radicals.

 

[Comeback City]

What exactly is the difference between something like (XY)2 and 2XY? I get that the 2XY would indicate 2 moles of XY, but I don't see why (XY)2 wouldn't be the same thing, so long as the whole formula is surrounded by parenthesis? thanks for any help

When a coefficient is placed in front of a molecule, that coefficient will show how many moles are present of the entire molecule following it.

When a subscript is placed after an atom or the parentheses of a molecule, that indicates how many moles of that specific atom or molecule (in parentheses) that is represents.

Let's examine Aluminum Carbonate...

5 Al₂(CO₃)₃

The coefficient 5 represents that there will be 5 moles of Al₂(CO₃)₃ molecules present.
The subscript 2 after Aluminum represents that for every molecule of Aluminum Carbonate, there will be 2 Al atoms present.
The subscript 3 after Oxygen represents that for every molecule of Carbonate, there will be 3 O atoms present.
The subscript 3 after Carbonate represents that for every molecule of Aluminum Carbonate, there will be 3 CO₃ molecules present.

Also, to find the number of moles of each individual atom/molecule, multiply the leading coefficient by all subscripts that apply to it. (ex: in the previous example there are 45 moles of Oxygen, found by multiplying coefficient 5 by subscripts 3 and 3)

(XY)2 means one mole of the species (XY)2, which contains two XY units bound together.

If it is a standalone molecule then yes. If there is another atom(s) or molecule(s) involved then they could each be individually bound to that other atom or molecule.