Question

May someone please help me understand oxidation numbers please? I really need help

Answer 1

so the point is how many electrons were taken from that atom

Answer 2

@jygebs I been told that, its just when it get to the problems that I did its just confusing. May I give you a sample problem?

Answer 3

Sure
What is the oxidation number of hydrogen in H2O?

Answer 4

@jygebs is it two?

Answer 5

how can you predicte it is 2 or -2?

Answer 6

nope it is +1.
oxygen takes two electrons. Then two hydrogen atoms lacks two electrons in total. Each lacks one so therefore +1 is its charge

Answer 7

but oxygen also get the -1 charge,tha how

Answer 8

than how?

Answer 9

no oxygen gets 2

Answer 10

Its starting to click in.. I don't know.. Thanks anyways for the help @jygebs

Answer 11

I get that but not for hydrogen

Answer 12

there is this order of which gets which charges

Answer 13

First, the alkali metals ALWAYS gets +1, alkali earth metals ALWAYS gets +2
Second, F is always -1, SO2 2-, NO3 -, etc
Third, Hydrogen is +1
Fourth, Oxygen is -2
Fifth the halogens are -2

Answer 14

From criteria 1, you go down the list and check the charges

Answer 15

Okay I think I get it now, @jygebs so a periodic table is required then

Answer 16

yup

Answer 17

do remember that in very strange instances that some of the state oxidation values provided by @jygebs may be different.

Answer 18

1. The OS of an individual atom is 0.
2. The total OS of all atoms in: a neutral species is 0 and in an ion is equal to the ion charge.
3. Group 1 metals have an OS of +1 and Group 2 an OS of +2
4. The OS of fluorine is -1 in compounds
5. Hydrogen generally has an OS of +1 in compounds
6. Oxygen generally has an OS of -2 in compounds
7. In binary metal compounds,
Group 17 elements have an OS of -1,
Group 16 of -2, and
Group 15 of -3.
Note: The sum of the OSs is equal to zero for neutral compounds and equal to the charge for polyatomic ion species.

http://chemwiki.ucdavis.edu/Analytical_Chemistry/Electrochemistry/Redox_Chemistry/Oxidation-Reduction_Reactions