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2008-04-29 03:14:56
twiistaaa
Member
+87|7092|mexico
im starting a chem subject next semester and ive decided to work on it abit now so i'm ready. its only a chem-101 type of course so don't worry that i completely suck at it now.

anyway, i was wondering how you figure out the charge when you name a molecule. for instance:

SF6 = Sulfur Hexafluoride, +6

i understand the naming and the cation-anion part, just not the charge. how do you get it?

also when does knowing the charge become useful? anytime you read about a molecule it doesn't list the charge in the name.
2008-04-29 03:30:46
Laika
Member
+75|6368
I don't think the +6 would be the charge if thats what you mean (can't tell from your Q). It might be the oxidation number or something like that but I can't tell as I don't have your chart and I don't remember that much from chemistry.
2008-04-29 04:19:51
Spark
liquid fluoride thorium reactor
+874|7099|Canberra, AUS
Ah.

That has to do with ionization, when a particle recieves a certain amount of energy, it loses an electron.

And yes, it is VERY useful.

When you read about molecules you'll generally hear about uncharged molecules. Charged atoms usually don't exist on their own, they bond with other charged atoms so both have full outershells. That's basically why atoms bond.

In this case, SF6+6 would just simply have been sulfur hexaflouride minus six electrons. That would of taken a fair bit of energy, but oh well...

BTW: "Charge" is closer to the meaning of "polarity" (if you do physics), protons have + charge, electons have - charge.

Last edited by Spark (2008-04-29 04:20:40)

The paradox is only a conflict between reality and your feeling what reality ought to be.
~ Richard Feynman
2008-04-29 04:38:02
PureFodder
Member
+225|6709
You need to know (or at least be able to predict) the oxidation state of the atoms involved. Flourine is pretty well always -1 Sulphur can be in various oxidation states, in this case it's +6. This gets the whole molecule to be neutrally charged.

Generally speaking, substances tend to be neutral as a whole for every positive charge there's something negative to counterbalance it. If not then the whole substance would repel itself (like charges repel) and fall apart. The reason anyone cares about charges is when molecules dissolve they can split into a cationic species and an anionic one. so salt (NaCl) turns into Na+ and Cl- which are entirely separated from each other. The reason people care about that is, say if you wanted to make, say, magnesium sulphate, how many magnesium ions would be needed per sulphate ion? In this case sulphate is SO4 2- and magnesium is 2+ hence the product would be MgSO4. If the sulphate ion was a 1- species then the formula would be Mg(SO4)2 hence you'd need twice as much sulphate.

The real arse comes about with atoms like sulphur which can have various oxidation states, depending upon what they're reacting with.

For working out charges, they will tend to loose/gain a specific number of electrons to complete their outermost valence shell typically:
group 1 metals are 1+
Group 2 metals are 2+
oxygen is 2-
noble gasses are 0
Halogens 1-
Hydrogen 1+
Nitrogen 3+
Carbon 4+

So a hydroxide ion (OH) has one oxygen (-2) one hydrogen (+1) so it is OH-.

You basicaly have to learn the typical oxidation states of common atoms.

 

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