Polyatomic Ions and Compounds

Polyatomic Ion –A group of atoms that tend to stay together and carry an overall ionic charge NH 4 + (ammonium) OH - (hydroxide) CO 3 2- (carbonate) PO 4 3- (phosphate) NO 3 - (nitrate) SO 4 2- (sulfate) ClO 3 - (chlorate) CrO 4 2- (chromate) HCO 3 - (hydrogen carbonate or bicarbonate) Cr 2 O 7 2- (dichromate) MnO 4 - permanganate)

Writing Formulas for Polyatomic Compounds To write a chemical formula for a polyatomic compound, follow these steps: 1. Write the symbols for each substance, with the positive first. 2. Write the ionic charge above each symbol. 3. Add more of the positive or negative ions until the total charges are balanced. 4. Write the formula using subscripts to indicate the number of ions of each type.

For Example – Sodium Sulfate

Example #2 – Calcium Hydroxide

Naming Polyatomic Compounds To name a polyatomic compound, 1. The positive ion is named first 2. The negative ion is named second. Do not change the ending of a polyatomic ion.

For example… 1. Sodium and phosphate 2. Na + CO3 3. K + SO4

Multi Valent Nomenclature. Some transition metals have more than one valence option. Ex. Sn, Au, Pb, Fe. For determining the name you need to first look at what it is paired with. Ex. Fe 2 O 3 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 match it. Thus the charge for iron MUST be +3 Then we write the name with roman numerals Iron(III)oxide

Practice Questions Pg 151 # 1-8

Multi Valent Cont’d When you are given the name you read the roman numerals to get the ionic charge of the element Ex. Nickel (II) phosphate –Ni has a charge of +2 according to the name –Phosphate has a charge of (-3) –The formula would be Ni 3 (PO 4 ) 2 –**REMEMBER ** Polyatomic Ions are treated as a unit. A subscript is put outside brackets to have a consistent charge