I was given $\ce{K2CrO4}$ and was asked to name the compound.

Can this be done by:

1) Determining the molecular compounds oxidation state


2) Does one need to memorize the polyatomic ions and that is the only way to know what is what?

  • $\begingroup$ There are many hows for nomenclature. #2 above is correct. $\endgroup$ – Brinn Belyea Sep 26 '14 at 1:41
  • $\begingroup$ Wow! My teacher gave us 24 to remember. $\endgroup$ – user137452 Sep 26 '14 at 1:44
  • $\begingroup$ Memorizing a small number (and 24 is a small number) of things is sometimes preferable. $\endgroup$ – Ben Norris Sep 26 '14 at 2:00

Definitely you need to remember it. Potassium Chromate is IUPAC name of $\ce{K2CrO4}$. There are other names such as Chromic acid and dipotassium salts. But mostly IUPAC names are accepted.

I don't think you should try to mug up all 24 names instead you should keep getting familiar with them when they come in reactions or somewhere else. After seeing them at few different places you will be remember them all. They will come very often while you are learning chemistry.

  • $\begingroup$ "I don't think you should try to mug up all 24 names" We're right around that time in General Chemistry classes where brute force memorization of all the polyatomic ions are necessary. ;) $\endgroup$ – LordStryker Sep 26 '14 at 12:33
  • $\begingroup$ @LordStryker In chemistry there are few stuff you need to memorize, which does not include small compounds :) $\endgroup$ – Freddy Sep 26 '14 at 12:36
  • $\begingroup$ According to the chemistry exams I write and administer, there are a lot of things you need to memorize. $\endgroup$ – LordStryker Sep 26 '14 at 12:42
  • $\begingroup$ @LordStryker Just now i am memorizing uses of each element of S-block. $\endgroup$ – Freddy Sep 26 '14 at 12:44

2 - Yes and no.

It is recommended to known common ions. They are, however, derived in uniform fashion from name of the element in latin. For example, for $Fe$ the name is Ferrum so anions are Ferrates. The 'fancy' part of the anion may consist either of naming the oxidation state (and optionally the number of oxygens and other atoms), i.e. (tetraoxo)ferrate(VI) or known suffixes and prefixes (hypochlorite-chlorite-chlorate-perchlorate, also hydro-, pyro-, orto- and meta- prefixes). Probably the easiest way to remember the second nomenclature would be to learn several (tens of) common ions and assume that isoelectronic ions have same prefixes and suffixed, but are derived from names of respective elements.

In practice, even though the first nomenclature is normative and is understood universally, the second is traditional and more common.

Some oxoions, however, have special names, like dithionite-ion.


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