DeusExMachina - 27-3-2003 at 19:08
ok, I'm totally new to this chemistry stuff and Darkfire has been kind enoguh to teach me chemistry over IM message conversations and email. I
understood most of the stuff (it took a while 
) I just have one question that I
dont get and Darkfire hasn;t been able to explain it to me fully because I always have to get off the computer whenever my brother tells me to...
anyways, to the question:
can someone explain to me what chemical formula is made when Ca and S come together? and also, how is this made? like, I know stuff like when two
atoms with the same charge come together (-2 and +2) there are no numbers in the formula. Darkfire, please reply to this topic and you can explain it
here and maybe I'll finally get it.
and if I dont, maybe someone else can tell me?
Basically, the question is: how are the numbers arranged and how do you know what numbers to use when you are trying to make a new compound with atoms
where one has a charge of - or + 2 and one has a charge of - or + 3. Obvioulsy both have to have different signs or else they can't be attractedd
to eachother to make an ionic compund.
thank you for your help.
vulture - 28-3-2003 at 07:40
There's a very simple trick for this called the cross rule.
It basically comes down to transferring the oxidation state of one atom to the index of the other.
Example:
Ca<sup>2+</sup> + PO<sub>4</sub><sup>3-</sup>
This only works if the ions have opposite charges ofcourse. What you do next is you write the oxidation state of Ca, 2, as the index of
PO<sub>4</sub> and vice versa:
Ca<sup>2+</sup> --> (PO<sub>4</sub>
<sub>2</sub>
and
PO<sub>4</sub><sup>3-</sup> --> Ca<sub>3</sub>
Finally:
Ca<sub>3</sub>(PO<sub>4</sub><sub>2</sub>
This method simply comes down to balancing charges, because (3x2<sup>+</sup> + (2x3<sup>-</sup> = 0
[Edited on 28-3-2003 by vulture]
DeusExMachina - 28-3-2003 at 08:10
that was exactly what darkfire was trying to tell me and I didn't get it... I'm stupid... I think a may even drop this chemsitry stuff all
together because it's confusing me.
DeusExMachina - 28-3-2003 at 10:42
ok, well, I'm starting to understand it more. I think I'll get it into my hed by tonight 
. I am going to get a book. Either a big chemistry dictionary or a book called chemistry made easy.
Thanks again for your help guys!
Blind Angel - 28-3-2003 at 13:57
If you want to know which charge has every element, just look at a periodic table, if you have one advanced enough to have the oxidation state wrote
on, choose the one in bold unless stated. If you only have a basic table: the most common element are in the two first row, so here how you do:
1 colum (alkali metal) they all have a +1 charge
2 colum: has a +2 charge
3 collum: (Borom) has +3
4 collum: (Carbon) has -4 or +4
5 colum: (Nitrogen) has -3
6 colum: (Oxygen) has -2
and halogen as -1
The las row are inert.
The trick is that their full layer must be full to be stable (every element tend to go to the most stable arrangement), the row in the periodic table
represent the number of electron in the last layer. Before carbon element will tend to GIVE an electron (add +1 to the other charge) and after carbon
they tend to TAKE an electron (add -1 to the other charge), Carbone and element in is row are special and can either give or take 4 electron. The last
row (Noble Gas) already have they last layer fill so they don't react.
Hope this help.
DeusExMachina - 28-3-2003 at 14:23
No, I already have my periodic table marked up with the charges but thanks anyways.
[Edited on 28-3-2003 by DeusExMachina]
Darkfire - 28-3-2003 at 15:52
Most of that will just confuse him more, ive tyed to make it simple, i havent even told him about certain elements having more than 1 charge.
Oxidation states and diferent valence will just be confusing. Its a lot of work teaching some one chemistry, but its better he learn from us than from
a teacher, as what they say always ends up being false or misleading unless you get a good teacher which come few and far between.
Dues if you dont get a chem book soon email me your shipping adress and ill send you mine.
CTR
Sparky - 28-3-2003 at 19:24
If you are interested in learning grade 11 chemistry, there is a textbook that I have used available for download here:
http://www.nepeanhs.com/index2.html
It generally explains things very well.
DeusExMachina - 28-3-2003 at 20:40
that's grade eleven chemistry? whoa, I'm only in grade eight. Anyways, I completely understand ionic bonds and all that stuff.
Darkfire - 28-3-2003 at 20:45
I wouldnt go that far but your getting better thats for sure.
CTR
DeusExMachina - 28-3-2003 at 21:02
well, what I meant is everything that you told me.