What are they? Is it really that important in Chemistry? How many are there? Did you memorise them? How long did it take?

It's useful because they pop up fairly often. It didn't take me too long (but I don't profess to know that many), and you should probably just print out a sheet of the common ones and try to learn them. The more chemistry you end up doing, the more ions you'll be using and thus the more you'll end up remembering. (You remember the common ones easily because you end up needing to know them a lot.)

poly atomic ions are simply molecules that have a charge. examples are:

 

OH-

H3O+

NO3-

NH4+

 

and so on.

 

it is best if you memorise them as poly atomic ions pop up everywhere.

I would suggest learning the names of about 10-15 of them. You'll enjoy it the rest of your life.

 

[ce]SO4^2- , PO4^3- , CO3^2- , HCO3^-[/ce]

 

These and the ones posted by insane_alien are all very common. You might find them in any article by your local newspaper, and in any science related article. Useful to know them no matter what the future will bring for you.

 

Wikipedia (as always) has a page on this topic.

 

I know about 30%-50% of all names in the list they provide on the page... they're not all equally common.

 

p.s. this topic doesn't belong in the organic chem. forum. Inorganic or general chemistry is better imho.

and for the halogens you only have to remember the ions for one of then (say Chlorine for instance) and the all the Other halogens ar easily transposed into the name.

 

Cl = chloride

OCl =hypo chlorite

ClO3 = chlorate

ClO4 =perchlorate

 

everything in Bold could just as easily be "Brom" "Iod" "Fluor"

Do perfluorates exist?

Perfluorates are unlikely to exist as F has no available d orbitals required for pi bonding

http://scidiv.bcc.ctc.edu/bg/poly.html

http://66.102.9.104/search?q=cache:Qvv3kAAUnyoJ:math-wizard.com/chemdata2.pdf+Perfluoric+Acid&hl=en&ct=clnk&cd=20&gl=uk&client=firefox-a

I can constuct a hypothetical perfluorate ion by analogy with perchlorate. I can put it on a list on a web page.

Is there any evidence of it really existing in macroscopic quantities?

If you wish to continue your education in the sciences I seriously suggest you pile these little beasts into your head...maybe 20 at the least. They are simple to memorize and will serve you well the rest of your career.

It's very useful (and sort of fun) to remember the most common ones, as pointed out multiple times already. Not only by name but by structure too, helps if you need to predict properties of the compounds that they are a part of.

What are they? Is it really that important in Chemistry? How many are there? Did you memorise them? How long did it take?

Knowing some oxidation numbers would help. If you know what oxidation number can a certain element have, then finding the oxidation number of any polyatomic ion would be just way easy!