I am beginning a chemistry course at my local TAFE and I have a problem, which I would be very gratefull if the knowledgeable members here could help
me out.
I am learning about predicting the formulas of ionic compounds using the octet rule and the periodic table.
I believe I have it under control as I have worked out some formulas correctly, but the problem is with one of the example's given in my text book.
Here it is as written in my book.
What is the formula for aluminium oxide?
1. Al is in group IIIA; so remove 3 electrons from an Al atom to give the ion Al3+
2. O is in group VIA; so add 2 electrons to give 8. The resulting ion is O2-
3. to make this formula electronically neutral: Al3+ ion is +3 and 2 ions gives a total charge of +6; O2- ion is -2 and 3 ions gives a total charge of
-6; +6 and -6 =0; therefor the formula is Al2O3.
Is this a mis-print in my text book should the total charges be +5 and -5 which would obviously still =0 and a formula of Al2O3, or am I missing
something.
From what I have worked out I think it's a mis-print and the 6 should be 5.
If this is the case I can move on in my study otherwise I must be not gettting something.
I know this question will be extremely basic for the vast majority of the members here, but we all had to start at the beginning at some time.
I would be very gratefull if someone could clear this up for me.Xenoid - 23-12-2007 at 20:35
Your statements 1, 2, and 3 look fine. Al2O3 is correct.
Where did the +5 and -5 come from ???~TCM~ - 23-12-2007 at 20:42
well doesn't +3 and 2 ions give a total charge of +5 and -2 and 3 ions -3.
I don't understand how +3 and 2 ions = +6.
I thought +3 and 2 ions = +512AX7 - 23-12-2007 at 20:47
Uh, multiplication?
You have three baggies. Each bag contains two pebbles. How many pebbles do you have in total? 2 + 2 + 2 = 3 * 2 = 6.
Didn't they teach this on Barney or something?
Tim
[Edited on 12-23-2007 by 12AX7]Xenoid - 23-12-2007 at 21:00
Quote:
Originally posted by ~TCM~
well doesn't +3 and 2 ions give a total charge of +5 and -2 and 3 ions -3.
I don't understand how +3 and 2 ions = +6.
I thought +3 and 2 ions = +5
No, it's 2 Al ions each with +3 charge, therefore 2 x +3 = +6
and
3 oxygen ions each with -2 charge, therefore 3 x -2 = -6~TCM~ - 23-12-2007 at 21:07
Thankyou Xenoid, now I understand.
I haven't actually started my course yet, so i'm trying to teach myself with the text books.
Your advice has helped me greatly.
My most sincere thank's.
