Poly-atomic Formulas and Names

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hey

Hi,

 

I would like to say thank you for taking your time to answer my question, in advance.

 

My quetsion is when you are writing the formula of a poly atomic substance how do you know the charge on one of the symbols. 

 

For example I am looking at gold (III) Nitrate. 

 

The steps in my book say to first get the symbols which  are : Au No3

Then it says to add the valences. Based on the periodic table, I see that Au has a valence charge of +1.  

The final answer it gives is Au(NO3)3

 

I am just unsure of how to go from the names and add the charges in. 

 

Please so steps. I am desperate. 

The method which you are using is applicable only on the elements of the representative elements of the periodic table.1 and 2 group and then 3,4,5,6,7 group 

Gold is a transition element and icharge on it is decided by the numbers written in roman numerals in the formula so Au3+ 

nitrate is a polyatomic ion and it is compulsory to know some basic polyatomic ions with their charges ...or you should have a good knowledge of making of lewis structures and formal charges 

Nitrate as -1 charge on it 

Au3+   and NO3- ...now make the formula.