Polyatomic Ions and Polyatomic Ions and CompoundsCompounds

Polyatomic IonPolyatomic Ion– A group of atoms that tend to stay together and carry A group of atoms that tend to stay together and carry

an overall ionic charge.an overall ionic charge.

+1 -1 -2 -3

NH4+

(ammonium) OH- (hydroxide) 

CO32-

(carbonate) 

PO43-

(phosphate) 

  NO3- (nitrate)  SO4

2- (sulfate)   

  ClO3- (chlorate) 

CrO42-

(chromate)  

 

HCO3- 

(hydrogen carbonate or bicarbonate) 

Cr2O72-

(dichromate)  

 MnO4

-

permanganate)    

   

Writing Formulas for Polyatomic Writing Formulas for Polyatomic CompoundsCompounds

To write a chemical formula for a polyatomic To write a chemical formula for a polyatomic compound, follow these steps:compound, follow these steps:

1. Write the symbols for each substance, with 1. Write the symbols for each substance, with the positive first.the positive first.

2. Write the ionic charge above each symbol.2. Write the ionic charge above each symbol.

3. Add more of the positive or negative ions until 3. Add more of the positive or negative ions until the total charges are balanced.the total charges are balanced.

4. Write the formula using subscripts to indicate 4. Write the formula using subscripts to indicate the number of ions of each type.the number of ions of each type.

For Example – Sodium SulfateFor Example – Sodium Sulfate

Example #2 – Calcium HydroxideExample #2 – Calcium Hydroxide

Naming Polyatomic CompoundsNaming Polyatomic Compounds

To name a polyatomic compound,To name a polyatomic compound,

1. The positive ion is named first1. The positive ion is named first

2. The negative ion is named second. Do 2. The negative ion is named second. Do not change the ending of a polyatomic ion.not change the ending of a polyatomic ion.

For example…For example…

1. Sodium and phosphate1. Sodium and phosphate

2. Na + CO32. Na + CO3

3. K + SO43. K + SO4

Multi Valent Nomenclature.Multi Valent Nomenclature.

Some transition metals have more than one valence Some transition metals have more than one valence option. option. Ex. Sn, Au, Pb, Fe.Ex. Sn, Au, Pb, Fe.For determining the name you need to first look at For determining the name you need to first look at what it is paired with. what it is paired with.

Ex. FeEx. Fe22OO33

Oxygen has a ionic charge of -2 so in total there is -6 as a Oxygen has a ionic charge of -2 so in total there is -6 as a charge for oxygen (3 x -2). Iron needs to match so 2 x (+3) will charge for oxygen (3 x -2). Iron needs to match so 2 x (+3) will match it. Thus the charge for iron MUST be +3match it. Thus the charge for iron MUST be +3

Then we write the name with roman numeralsThen we write the name with roman numeralsIron(III)oxideIron(III)oxide

Practice QuestionsPractice Questions

Pg 151 # 1-8Pg 151 # 1-8

Multi Valent Cont’dMulti Valent Cont’d

When you are given the name you read the When you are given the name you read the roman numerals to get the ionic charge of the roman numerals to get the ionic charge of the elementelement

Ex. Nickel (II) phosphateEx. Nickel (II) phosphate– Ni has a charge of +2 according to the nameNi has a charge of +2 according to the name– Phosphate has a charge of (-3)Phosphate has a charge of (-3)

– The formula would be NiThe formula would be Ni33(PO(PO44))22

– **REMEMBER**REMEMBER****Polyatomic Ions are treated as a unit. Polyatomic Ions are treated as a unit.

A subscript is put outside brackets to have a A subscript is put outside brackets to have a consistent chargeconsistent charge