[unsavedhero]

I know this is an extremely easy question, but I'm stumped . Nitrogen has an atomic number of 7 and oxygen has an atomic number of 8. So I would assume that it is 7 + 8 + 8 which is 23 electrons. However someone told me it is 24 electrons because NO₂ has a charge of -1 which means it has an excess electron. However doesn't that break the law of conservation of mass? Where does the extra electron come from? Thank You =)

[magician4]

there is the nitrogen dioxide molecule NO₂ , with 23 electrons total ( i.e. a free radical, and violating the octet rule at that)
it's an uncharged particle

also, there is the nitrite ion NO₂^- , with 24 electrons total
it obeys the octet rule and bears a single negative charge

i.e.: two different species, and both exist in their own right

However doesn't that break the law of conservation of mass?

I'm not sure that I understand the what you're asking, i.e. how the conservation of mass possibly could be violated here. Could you pls. expand on this?

Where does the extra electron come from?

like always in chemistry: from someone else, who in return became a positively charged cation

regards

Ingo

[unsavedhero]

what I am saying is that the NO₂ ion is made up of 1 nitrogen and 2 oxygens. The nitrogen has 7 electrons in total and the oxygens have 16 electrons in total. when you add 7 and 16 you get 23... so where did that extra electron come from to make 24 electrons if there are only 23 electrons between the N and two Oxygens.

[magician4]

the moment you "add" a further electron to nitrogen dioxide, it will have one more electron ( i.e. 24 instead of previously 23 ) and will have become a different species, the nitrate anion.

the very electron has to come from elsewhere, i.e. from some electron donating process (oxidation)

(not sure if this reaction exists , but as a hypothetical example, by reaction with potassium:
K + NO₂  K⁺ + NO₂^- = KNO₂ )


regards

Ingo