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### Formula units vs molecule

Posted: Thu Oct 03, 2019 3:32 pm
What are formula units? Can a formula unit be the same thing as a molecule or atom? (E.21 and E.25 ask about this)

### Re: Formula units vs molecule

Posted: Thu Oct 03, 2019 3:43 pm
A formula unit can be thought of as the empirical formula for an ionic compound. For example, NaCL is the formula unit for sodium chloride.

### Re: Formula units vs molecule

Posted: Thu Oct 03, 2019 3:54 pm
This excerpt from the book cleared that up for me because I was stumped on the idea of formula units too.
" e molar mass of an element is the mass per mole of its atoms.
e molar mass of a molecular compound is the mass per mole of its molecules.
e molar mass of an ionic compound is the mass per mole of its formula units."

This one too "Once you know the molar mass of a compound, you can use the same technique that was used for elements to determine how many moles of molecules or formula units are in a sample of a given mass." So basically, it's just another word for moles of molecules!

### Re: Formula units vs molecule

Posted: Thu Oct 03, 2019 4:28 pm
For questions asking for formula units of a molecule, the unit for your answer should be atoms. So I think these questions are asking you to find N (i.e., number of molecules).

### Re: Formula units vs molecule

Posted: Fri Oct 04, 2019 1:41 am
molecules are able to be broken down into their individual atoms. on the other hand, formula units are ionic or covalently bonded so they are unable to be broken down any farther. the formula unit for these compounds is just the lowest possible ratio for that compound

### Re: Formula units vs molecule

Posted: Fri Oct 04, 2019 1:15 pm
A formula unit is the lowest ratio of ions in an ionic compound. This means that it is the smallest unit of an ionic compound. A molecule is when two or more elements are bonded together specifically in covalently bonded compounds.

### Re: Formula units vs molecule

Posted: Fri Oct 04, 2019 8:56 pm
In terms of how the differ equation wise for formula units you are going to divide the grams of the compound by the molar mass of the compound and then multiply by Avogadro's number whereas if you were looking for how many atoms of lets say oxygen are in an ionic compound you would take the grams of the compound divided by the molar mass of the compound and then multiply by Avogadro's number and by the amount of oxygen molecules/1 mole of the compound. I also agree that your answer will be in atoms because you are doing the conversion from moles to atoms.

### Re: Formula units vs molecule

Posted: Sat Oct 12, 2019 12:52 am
Formula units work the same way as do molecules and atoms through Avogadro's number. According to the book, the key difference is that formula units pertain to ionic compounds, whereas molecules are of molecular compounds and atoms are of elements. If you want to check it out yourself, the information is at the section E.2 Molar Mass on the page labeled F40 (online PDF).