How do you find an oxidation number of an element in a compound?

Answer 1

#"The oxidation number of an element in a compound........."#

When all bonding pairs of electrons are formally broken and the charge is distributed to the most electronegative atom, the element's oxidation state remains on the atom of interest.

This definition is, I grant, a mouthful, but let's see how it is applied. We start with the water molecule, #OH_2#, which of course is neutral. The #O-H# bond is of course composed of 2 electrons (this goes back to the idea of covalent bonds as the result of the sharing of 2 electrons between adjacent atoms), and when we break this bond, we are left with #O^(2-)# and #2xxH^+# (because oxygen is more electronegative than hydrogen, the 2 electrons in the bond devolve to oxygen). Thus given the definition, the oxidation state of #O# #=# #-II#, and that of #H# #=# #+I#.

Elements, of course, are considered to have #0# oxidation states, because in their elemental state they neither accepted not donated electrons: cf oxidation of carbon:

#C(s)+O_2(g)rarrCO_2(g)#

Elemental carbon is conceived to have been oxidized, i.e. it has lost 4 electrons to give #C(IV+)#, and dioxygen has accepted those same electrons to give #2xx(-II)#.

Now of course, these ideas of electron loss and electron gain are formalisms in that they have no actual reality, but often they allow us to balance redox reactions. I can give you a few ions with the oxidation numbers assigned: #CO_3^(2-), C(+IV)#; #SO_3^(2-), S(+IV)#; #SO_4^(2-), S(+VI)#; #ClO_4^(-), Cl(+VII)#; #ClO_3^(-), Cl(+V)#.

In any case, I hope that this spray hasn't completely confused you; keep in mind that these are straightforward concepts with extremely basic arithmetic.

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Answer 2

Cameron Andrews

To find the oxidation number of an element in a compound, you follow these steps:

Determine the oxidation number rules and exceptions.
Assign known oxidation numbers to elements with fixed oxidation states.
Apply algebraic rules and the charge neutrality of the compound to find the oxidation number of the unknown element.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.