POLYATOMIC COMPOUNDS Chapter 5.9

Polyatomic Ions Poly - more than one or many Atomic – made of atoms Polyatomic Ion - groups of atoms that tend to stay together and carry an overall ionic charge. Example: Nitrate ion = NO 3 -

Looking at the top center of your Periodic Chart of Ions handout you will see examples of these. Examples: CO 3 2- Carbonate NO 3 1- Nitrate Note: you will know the difference between a regular non-metal ion and a polyatomic ion by the fact that there is no “ide” ending on the polyatomic ion. Polyatomic Ions

These can bond with other elements to form ionic compounds. Example: Na + and NO 3 - form NaNO 3 Just like other ionic compounds NaNO 3 has a net charge of “0”. Polyatomic Compounds

Polyatomic Ions When a compound containing a polyatomic ion is dissolved in water, the positive metal ion and the nitrate ion separate from each other, but the nitrate ion itself stays together as a unit surrounded by water molecules.

WRITING FORMULAS FOR POLYATOMIC COMPOUNDS All the compound formula calculations and compound naming procedures are the same as for regular ionic compounds. EXAMPLE: What is the formula for the ionic compound formed by sodium and sulfate ion?

STEPS 1) Write the symbols of the metal and of the polyatomic group Na SO 4 2) Write the ionic charges Na +1 SO ) Choose the number of ions to balance the charge Na +1 Na +1 SO 4 -2

STEPS 4) Write the formula using subscripts. Na 2 SO 4 You could use the criss-cross rule if you wanted to.

EXAMPLE 2 What is the formula for lead (IV) carbonate? 1) Pb CO 3 2) Pb +4 CO ) Pb +4 CO 3 -2 CO ) Pb(CO 3 ) 2

EXAMPLE 3 What is the name of Ca(NO 3 ) 2 ? Go through the steps backwards. Solution: Calcium Nitrate

PRACTICE QUESTIONS PAGE 198; 3 abce, 4 abd

SOLUTIONS 3a) Na 3 PO 4 3b) CaSO 4 3c) KClO 3 3e) Be(N0 3 ) 2 4a) Potassium Carbonate 4b) Sodium Sulfate 4d) Silver Nitrate