# Why is the relationship between a compound in its elements expressed in moles or particles? Is there a law dedicated to this? [closed]

I understand that a ratio can be made for the number of elements in a compound and the actual compound. Depending on the need, different units can be used. It can be both moles. It can also be entities where the entity is an ion, molecule or atom.

For example, in $$NO_3$$ a ratio can be made where 3 mol of O is to 1 mol of $$NO_3$$. Another ratio is 3 atoms of O is to 1 formula unit of $$NO_3$$. What is the law that says this, and why can different units be used for this formula? What are the other possible units aside from mole and particles? Why are moles or particles the basis?

I know the topic is fairly simple but most discussions I've seen just focus on other things. For example, there is more emphasis Law of Definite Proportions and Multiple Proportions. Then when the part where this ratio is used in other lessons such as percentage composition or conversions between mass, mole, and atom they just briefly explain that you can make a ratio because that's how it is presented in chemical formula. I mean I can accept it but I'd like a little more explanation that really focuses on ratio between a compound and an element it contains. It's not that I don't completely get it but I'd like a more intuitive grasp.

• Do you got this bit about how proportion works? Unit is irrelevant. Jul 22, 2022 at 0:19
• " a ratio can be made for the number of elements in a compound and the actual compound" Sorry but this is unclear. What do you mean with "number of elements in a compound"? For instance, in methane there are two different elements. Is that what you mean? Jul 22, 2022 at 5:33
• It is like a common sense law, not related to chemistry, applied since ancient times, e.g. for scaleable cooking. Jul 22, 2022 at 6:49