Confused about subscripts and coefficients wrt forumulas

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Discussion Overview

The discussion revolves around the interpretation of subscripts and coefficients in chemical formulas, specifically comparing expressions like (XY)2 and 2XY. Participants explore the implications of these notations in terms of moles and molecular structure, touching on both theoretical and practical aspects of chemical representation.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants assert that 2XY indicates two moles of the species XY, while (XY)2 represents one mole of a compound that consists of two XY units bound together.
  • One participant provides an example, stating that (CN)2 is a molecule of cyanogen, emphasizing that the notation (XY)2 highlights the binding of two units rather than simply counting atoms.
  • Another participant explains that a coefficient in front of a formula indicates the number of moles of the entire molecule, while subscripts denote the number of specific atoms or groups within that molecule.
  • There is a reiteration that the interpretation of (XY)2 as a standalone molecule may vary depending on the context, suggesting that additional atoms or molecules could alter its representation.

Areas of Agreement / Disagreement

Participants express differing views on the implications of the notations, with some agreeing on the basic definitions while others question the context and specificity of the examples provided. The discussion remains unresolved regarding the broader implications of these notations in different chemical contexts.

Contextual Notes

Participants note that the interpretation of chemical formulas can depend on the context in which they are used, and the discussion highlights the complexity of representing molecular structures accurately.

instantresults
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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
 
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Without context impossible to answer.

Example for (XY)2 ? Standalone ? Or did you just make that up ?
 
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.
 
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instantresults said:
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)

mjc123 said:
(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.
 

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