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Naming Compounds

Posted: Wed Oct 03, 2018 8:23 pm
by Emma Scholes 1L
Can someone explain how to write the formula of compounds.

For example, in question E9 it asks you to write the formula for magnesium sulfate heptahydrate.

Re: Naming Compounds

Posted: Wed Oct 03, 2018 8:41 pm
by Ahmet_Dikyurt_3L
Can someone explain how to write the formula of compounds.

For example, in question E9 it asks you to write the formula for magnesium sulfate heptahydrate.

You need to know the basic formulas. Some names give you clues such as ending with -ate or -ite means there is oxygen in the compound. There are also prefixes for numbers of atoms like di-, tri-, and hepta- (which is 7), and you should memorize the first 10 which isn't hard. If there's -ide, it means there are a minimum of two different elements. You should also remember about covalent bonds and how many atoms do you need to fill the outer shell. There are some with special names like White Phosphorus (mentioned in M11) which is P4, but I just look them up. You will most likely can't name every single compound but these are some tips you can use. I probably missed some tips, so please add on, if you read this. Feel free to fix me if I made a mistake, pobody's nerfect

Re: Naming Compounds

Posted: Wed Oct 03, 2018 10:11 pm
by Annalyn Diaz 1J
Per Dr. Lavelle, over time you'll pick up how to name compounds through working through more problems just like this.

To add further elaborate on the post above:

-ite : used when the same compound has lesser amount of oxygen (ex. phosphite, PO3)
-ate: used when the same compound has the larger amount of oxygen (ex. phosphate, PO4)
(Note that the phosphate has the greater amount of oxygen, so it has the suffix -ate)

Going along with oxygen, the prefixes hypo- and per- are thrown in when there's more than just two possibilities. Hypo- goes with -ite, and per- goes with -ate. For example, let's use the anion chloride, Cl- :

hypochlorite: ClO-
chlorite: ClO2-
chlorate:ClO3-
perchlorate:ClO4-

Hope this helps!

Re: Naming Compounds

Posted: Wed Oct 03, 2018 10:37 pm
by Carissa Young 1K
Another thing to note is hydrate refers to water, so it's formula is simply H20. It helps to break down the name into parts and figure out what they mean individually and then put it all together at the end.

Ex. hepta/ hydrate
Hepta means 7
Hydrate refers to water

Therefore heptahydrate is 7H20

Re: Naming Compounds

Posted: Wed Oct 03, 2018 10:41 pm
by haleyervin7
Hi, I had a similar question, except I was also wondering how you know the state of each compound when it is not given.

Re: Naming Compounds

Posted: Wed Oct 03, 2018 10:46 pm
by haleyervin7
Hi, I had a similar question, except I was also wondering how you know the state of each compound when it is not given.

Re: Naming Compounds

Posted: Wed Oct 03, 2018 11:26 pm
by Andre_Galenchik_2L
So is the molecular formula for magnesium sulfate heptahydrate MgS7H2O? I am not even sure if that is how the formula is written, for example is the 7 supposed to be distributed like so: MgSH14O7?

Re: Naming Compounds

Posted: Thu Oct 04, 2018 10:06 am
by Sophia Ding 1B
I saw that you used S, which is actually sulfur rather than sulfate. The compound of sulfate is actually SO4, so the molecular formula for magnesium sulfate heptahydrate is MgSO4(H2O)7. I personally like to keep the 7 separate to help me remember that there are 7 moles of H2O within this compound, but you can also distribute it for example like MgSO11H14. I think it's easier to read as the first way I wrote out, but I'm not sure as to which one is seen as more "correct."

Re: Naming Compounds

Posted: Thu Oct 04, 2018 11:06 am
by Aidan Ryan 1B
Replying to haleyervin7.
The elements themselves are either solids, liquids or gasses at STP. For compounds in a single or double displacement you can assume they are in water I believe unless otherwise stated. From that if you know if the salt is soluble it is aqueous and if insoluble its a solid. The reactants usually end up soluble but something can solidify out. Also some compounds like CO2, C2H4 and NO are gasses at room temp. A lot of it is just knowing the compound I think.

Re: Naming Compounds

Posted: Thu Oct 04, 2018 7:40 pm
by becca_vandyke_4b
For the states of the compounds you also have to know if they are soluble or not (but he said we don't need to know the rules yet) but anyways some compounds like those with NO3- are soluble in water so they become aqueous. I think you can just look at a solubility chart right now for the problems and we'll memorize it later.