Confused about subscripts and coefficients wrt forumulas

In summary, the main difference between something like (XY)2 and 2XY is that the former represents one mole of a molecule made up of two XY units bound together, while the latter represents two moles of the species XY. The placement of coefficients and subscripts can change the interpretation of a chemical formula and it is important to understand these differences in order to accurately represent and calculate chemical reactions.
  • #1
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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  • #2
Without context impossible to answer.

Example for (XY)2 ? Standalone ? Or did you just make that up ?
 
  • #3
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.
 

Related to Confused about subscripts and coefficients wrt forumulas

1. What is the difference between subscripts and coefficients in formulas?

Subscripts refer to the small numbers written to the right of an element or compound in a chemical formula, while coefficients refer to the numbers written in front of a compound or element. Subscripts indicate the number of atoms of each element in a molecule, while coefficients indicate how many moles of a compound are present in a reaction.

2. How do I know when to use subscripts or coefficients in a formula?

Subscripts are used to correctly represent the chemical composition of a molecule, while coefficients are used to balance chemical equations. Subscripts should not be changed when balancing equations, only coefficients should be adjusted.

3. Can subscripts and coefficients be used interchangeably in formulas?

No, subscripts and coefficients have different meanings and cannot be used interchangeably. Subscripts represent the number of atoms in a molecule, while coefficients represent the number of moles of a compound in a reaction.

4. How do subscripts and coefficients affect the overall charge of a molecule?

Subscripts do not affect the overall charge of a molecule, as they only indicate the number of atoms present. However, coefficients can change the overall charge of a molecule if they are used to balance an equation involving ions.

5. Is it possible to have a coefficient as a subscript or vice versa?

No, subscripts and coefficients have different positions and roles in a formula. Subscripts are always written as small numbers to the right of an element, while coefficients are always written in front of a compound or element. It is not possible to have a coefficient as a subscript or vice versa.

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