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how do books define "formula unit"?

how do books define "formula unit"?

Undergrad books? (I think the term isn't used in GCSE or A level)
(edited 1 year ago)
Formula unit is a term used in chemistry to refer to the simplest ratio of atoms in a chemical compound. For example, the formula unit for water is H2O, indicating that there are two hydrogen atoms for every one oxygen atom. This term is typically used in undergraduate chemistry courses, so you may not find it covered in GCSE or A level textbooks. Some examples of undergraduate books that may have a definition of formula unit include "Introduction to General, Organic, and Biological Chemistry" by Karen Timberlake and "Chemistry: The Central Science" by Theodore L. Brown
Reply 2
Original post by dulladulla
Formula unit is a term used in chemistry to refer to the simplest ratio of atoms in a chemical compound. For example, the formula unit for water is H2O, indicating that there are two hydrogen atoms for every one oxygen atom. This term is typically used in undergraduate chemistry courses, so you may not find it covered in GCSE or A level textbooks. Some examples of undergraduate books that may have a definition of formula unit include "Introduction to General, Organic, and Biological Chemistry" by Karen Timberlake and "Chemistry: The Central Science" by Theodore L. Brown

Well,

That definition "the simplest ratio of atoms in a chemical compound." is a problematic definition because that doesn't seem to distinguish it from the term empirical formula. Do you have any of the books that you mention such that you'd be able to show the definition in one of them?

Thanks
(edited 1 year ago)
Original post by gazbo1
Well,

That definition "the simplest ratio of atoms in a chemical compound." is a problematic definition because that doesn't seem to distinguish it from the term empirical formula. Do you have any of the books that you mention such that you'd be able to show the definition in one of them?

Thanks


I understand where you're coming from, as the definition of formula unit can be a bit confusing at first.

Here's a little more detail on the difference between formula unit and empirical formula:

Formula unit is the simplest ratio of atoms in a chemical compound, without regard to the arrangement of atoms in the molecule. It represents the minimum number of atoms required to make up a chemical compound.
Empirical formula, on the other hand, represents the simplest whole-number ratio of atoms in a molecule. This means that the empirical formula shows the relative number of atoms in a molecule, but not the actual number of atoms.
For example, let's take the compound methane (CH4). The formula unit for methane would be CH4, as this represents the simplest ratio of atoms (one carbon atom and four hydrogen atoms). The empirical formula for methane would be CH2, as this represents the simplest whole-number ratio of atoms (one carbon atom and two hydrogen atoms).

I hope this clears things up a bit.
Reply 4
Original post by dulladulla
I understand where you're coming from, as the definition of formula unit can be a bit confusing at first.

Here's a little more detail on the difference between formula unit and empirical formula:

Formula unit is the simplest ratio of atoms in a chemical compound, without regard to the arrangement of atoms in the molecule. It represents the minimum number of atoms required to make up a chemical compound.
Empirical formula, on the other hand, represents the simplest whole-number ratio of atoms in a molecule. This means that the empirical formula shows the relative number of atoms in a molecule, but not the actual number of atoms.
For example, let's take the compound methane (CH4). The formula unit for methane would be CH4, as this represents the simplest ratio of atoms (one carbon atom and four hydrogen atoms). The empirical formula for methane would be CH2, as this represents the simplest whole-number ratio of atoms (one carbon atom and two hydrogen atoms).

I hope this clears things up a bit.



Regarding that explanation about minimum number of atoms for the compound..and without regard for the arrangement.. Molecular formula H2O doesn't tell you any more or less about the arrangement than formula unit H2O does. And empirical formula too doesn't tell you more about the arrangement. So this whether it tells you about the artangement seems like a strange distinction

Also, when I look up CH2 though, I get Methylene rather than Methane. Also 1:4 (what CH4's ratio is), is already as simplified as possible. The ratio already has the smallest whole numbers that it can.

So it looks to me like for Methane/CH4, the molecular formula and empirical formula are the same. CH4.
(edited 1 year ago)
Formula unit is used for ionic compounds whereas empirical formula is used for molecular substances. Ionic compounds are not molecular so empirical formula, strictly speaking does not apply, even though it would give the same answer as the formula unit. The formula of an ionic compound is always given as the formula unit. E.g MgCl2.
Reply 6
Original post by Old man1234
Formula unit is used for ionic compounds whereas empirical formula is used for molecular substances. Ionic compounds are not molecular so empirical formula, strictly speaking does not apply, even though it would give the same answer as the formula unit. The formula of an ionic
compound is always given as the formula unit. E.g MgCl2.


Looks like formula unit can apply for giant covalent network solid structures too. Macromolecules like diamond.

https://en.wikipedia.org/wiki/Network_covalent_bonding

And indeed they're not molecular. (not molecular, in the sense of, they're not composed of molecules)

I guess Methane CH4 won't have a formula unit? (an earlier poster thought it did but I don't think so 'cos it's a molecule/covalent). And I suppsoe an ion pair wouldn't have a formula unit 'cos while ionic in terms of electronegativity, it's not ionic in assembly,

I guess if you define empirical formulae as simplest whole number ratio of a molecular formula, then indeed the term emirical formula wouldn't apply to ionic compounds. But according to https://en.wikipedia.org/wiki/Chemical_formula#Empirical_formula Empirical formula does apply to ionic compounds so a formula unit would be an empirical formula in an ionic compound.

Also I think a funny feature of the term formula unit is it might refer to the component of the actual substance.. But it can also refer to the formula (formula of the formula unit).

In contrast, when it comes to molecules we distinguish between The Molecule, and The Molecular Formula.

Formula unit can be either a formula, (which represents the component of the substance), or it can be the component of the substance itself.

Is K2S2O4 ionic? I think that might be an example of one where the formula unit is different to the empirical formula. Empirical formula would be KSO2
(edited 1 year ago)

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