I am aware that since 2005, IUPAC guidelines established that hydrogen is more electronegative than all elements from group V in the periodic table (you can check official documentation). Thus, $\ce{NH3}$ is now named nitrogen trihydride and $\ce{PH3}$ is phosphorous trihydride. Nevertheless, now I am revisiting some material regarding chemical equations balancing and I found this reaction as an example:

$$\ce{4 ClO3- + 3 N2H4 -> 6 NO + 4 Cl- + 6 H2O}$$

In this reaction, $\ce{Cl^5+}$ reduces to $\ce{Cl^1-}$ and, supposedly, nitrogen (-2) from $\ce{N2H4}$ (hydrazine) oxidises to nitrogen +2 in $\ce{NO}$. Nevertheless, according to the new rules, nitrogen in hydrazine should have a positive oxidation number (+2) and hydrogen a negative one (-1). In such a case, there wouldn't be a redox reaction since nitrogen's oxidation number is not changing. So, what is the final answer? Are IUPAC ruled not applicable? or, based on the new guidelines, is this reaction not a redox type anymore?

  • $\begingroup$ Chlorine's oxidation state is changing, so it must be a redox. Unless... were the oxidation state guidelines for any elements besides hydrogen changed? $\endgroup$
    – unstable
    Commented Apr 7 at 3:30
  • $\begingroup$ If Cl goes from +$5$ to $-1$, Hydrogen must go from $-1$ to $+1$, and nitrogen stays at +$2$, as strange as it may look. . $\endgroup$
    – Maurice
    Commented Apr 7 at 12:21

1 Answer 1


The guidelines for naming compounds do not coincide with the guidelines for oxidation state, because:

(1) the formal electronegativity order for compound naming does not match the actual electronegativities of the elements as determined by bond polarities or electronic properties of the atoms;

(2) since 2016, oxidation state is defined in terms of molecular-orbital structure, which correlates with electronegativity differentials most but not all of the time (see here).

In the case of ammonia, the molecular-orbital structure is rendered as it has always been: the occupied (bonding) orbitals are polarized towards nitrogen, so that element is given the negative oxidation state no matter how we name the compound.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.