Understanding Polyatomic Ions in Lewis Structures

[bjon-07]

Hi everybody, I am new to PF and thus far have found it very interesting and helpfull.

I have a chemistry question, my test is tomorrow.

I know how to draw lewis strutures in general. But i have a question concering polyatomic ions,

from what i have learned you should treat each ion seperatly.

but on the compound KH2PO4 the struture looks like thus
H--O O
\ / (the lines should contact the p to the o's
P but for some resonce i can't make it work)
/ \
H--O O
sense PO4 is an polyatomic ion why isn't is seperate

my other question (which more critically of the two) is the structure of HCN and HN03

in both of the stutures the h is attaced to the struture. But both contain polyatmoic ions, cyanide and nitrate.

why are they seperate?

Does have something to do with them being acids( my not sure if they are acids, we have not covered acid in my chem text yet).

thank you for your help

Brandon

 

[ShawnD]

The PO4 is not separated from the H2 because H2PO4 is itself a polyatomic ion.

HCN and HNO3 separate because they are not polyatomic ions; they are simply acids just as you said :).

Here is a list of polyatomic ions for future referance
http://www.woodrow.org/teachers/chemistry/links/chem1/PolyatomicIonsChart.html

 

[bjon-07]

thank you for your help. The list of polyatomic ions i was using is small and only contains a few of the hundrens of them out their. Thank your replie and the list.