Im currently doing my standard grade chemistry course and need your help.. I can't get the hang of valency numbers :(
My teacher shout at me beacuase i dont understand :'(
Please some one help me!
2006-11-03 19:58:18 · 4 answers · asked by George 2 in Science & Mathematics ➔ Chemistry
Valency number is the combining power of an atom or group of atoms and is used to work out the formulae of compounds. It used to be defined as how many hydrogen atoms am atom or group could combine with or displace. Nowadays it is the number of electrons the element or group can give, take or share. A sodium atom will give away one electron so it has a valency number of +1. Chlorine will take an electron so it has a valency of -1. When working out the formula of a compound the valency numbers must add up to zero. So in sodium chloride there is one of each atom as the +1 and -1 add up to 0. The formula is NaCl. The group sulphate SO4 has a valency number of -2 and so in sodium sulphate you would need two sodiums (each +1) for one sulphate and so the formula of sodium sulphate is Na2SO4. Copper has a valency of +2 so copper sulphate would have one copper and one sulphate group (+2 and -2 = 0) so its formula is CuSO4. If you end up with a formula with more than one of a group - the group has to be enclosed in brackets as in Copper nitrate where the nitrate, NO3 is -1 and the copper is +2 you need 2 nitrates. The formula is Cu(NO3)2
Carbon can share 4 electrons and hydrogen can share 1 electron. So carbon is considered as -4 and hydrogen +1. The formula for the simplest compound of carbon and hydrogen is therefore CH4 (methane).
2006-11-04 01:16:40 · answer #1 · answered by Anonymous · 0⤊ 0⤋
Do you mean how do you work out the charge on an ion in a compound? If so, here it is....you need to know that for groups 1 - 4, valency = group number and is positive, and for groups 5 - 7, valency = 8-group number and is negative.
So...if an element is in group 1 its valency is 1+, group 2 is 2+....etc....group 7 is 1-, group 8 is 2- etc.
Where it gets tricky is in the transition metals, where valency is variable. If you need to work that out, you just use the information above to work out valency for everything else in the compound, then you can work out the transition metal valency.
For instance, valency of Mn in MnO4^- can be calculated as follows : O is group 6 so valency is 2-...there's 4 O's so (4 x 2-) = 8-. The charge on the ion MnO4^- is 1-...so Mn must be 7+ since 7+ added to 8- gives 1-.
2006-11-04 13:31:45 · answer #2 · answered by drjaycat 5 · 0⤊ 0⤋
Perhaps your teacher has`nt a clue either, I have to say valency with me was a long time ago, so I won`t waffle, what I will say is this,
If your teacher cannot explain something he or she is teaching and/or is not capable of explaining to you some thing that you do not understand resulting in you having to resort to this "forum" to get an answer, then I think that the teacher should be hauled before the head to explain his/her actions. A really poor show.
Speak to your parents.
2006-11-06 14:00:21 · answer #3 · answered by Spanner 6 · 0⤊ 0⤋
Not sure what part of valency numbers you are having problems with but here are some sources for you to check out to help you understand them:
2006-11-04 04:18:51 · answer #4 · answered by MonkeyLab 2 · 0⤊ 0⤋