1. Unit 4: Polyatomic Ions and Ionic Bonding

2. Polyatomic Ions Polyatomic ions are two or more atoms covalently bonded that have a charge. Polyatomic ions are two or more atoms covalently bonded that have a charge. NH 4 + SO 4 2- OH - NO 3 -

3. Writing Formulas with Polyatomic Ions Follow same guidelines as binary ionic compounds except you must treat the polyatomic ion as a single unit. Follow same guidelines as binary ionic compounds except you must treat the polyatomic ion as a single unit. Write formulas for the ions with charges. Remember cation first! Write formulas for the ions with charges. Remember cation first! NH 4 + CO 3 2- NH 4 + CO 3 2- It is sometimes helpful to put parenthesis around the formula and leave the charges outside the parenthesis before criss-crossing! It is sometimes helpful to put parenthesis around the formula and leave the charges outside the parenthesis before criss-crossing! (NH 4 ) + (CO 3 ) 2- (NH 4 ) + (CO 3 ) 2-

4. Criss-cross the charges into subscripts (Leaving out the + and – signs). Criss-cross the charges into subscripts (Leaving out the + and – signs). If a subscript is needed for the polyatomic ion, you must enclose the polyatomic ion in parenthesis. If a subscript is needed for the polyatomic ion, you must enclose the polyatomic ion in parenthesis. (NH 4 ) + (CO 3 ) 2- Simplify the numbers to lowest terms if needed. Simplify the numbers to lowest terms if needed. (NH 4 ) 2 CO 3 (NH 4 ) 2 CO 3 Remember, never simplify the polyatomic ion subscripts, only the subscript outside the parenthesis!!!! Remember, never simplify the polyatomic ion subscripts, only the subscript outside the parenthesis!!!!

5. Examples Cu 2+ NO 3 - Cu 2+ NO 3 - Cu 2+ (NO 3 ) - Cu 2+ (NO 3 ) - Cu(NO 3 ) 2 Cu(NO 3 ) 2 Li + PO 4 3- Li + (PO 4 ) 3- Li 3 PO 4 Parenthesis are removed because only 1 phosphate ion is needed!

6. Memorizing Polyatomic Ions JUST DO IT!!!!! JUST DO IT!!!!! One tip to make it easier: One tip to make it easier: Memorize the “-ate” ion and then know: Memorize the “-ate” ion and then know: “ite” ending has one less oxygen than “ate” ion “ite” ending has one less oxygen than “ate” ion “Per” “ate” has one more oxygen than “ate” ion “Per” “ate” has one more oxygen than “ate” ion “Hypo” “ite” has 2 less oxygens than “ate” ion “Hypo” “ite” has 2 less oxygens than “ate” ion Chlorate ClO 3 -1 Chlorite ClO 2 -1 Perchlorate ClO 4 -1 Hypochlorite ClO -1

7. Polyatomic Ions sulfate SO 4 2– sulfate SO 4 2– sulfite SO 3 2– sulfite SO 3 2– phosphate PO 4 3– phosphate PO 4 3– phosphite PO 3 3– phosphite PO 3 3– nitrate NO 3 –1 nitrate NO 3 –1 nitrite NO 2 –1 nitrite NO 2 –1

8. Monatomic Metal Ions aluminum Al 3+ aluminum Al 3+ cuprous (or Copper I)Cu + cuprous (or Copper I)Cu + cupric (or Copper II)Cu 2+ cupric (or Copper II)Cu 2+ ferrous (or Iron II)Fe 2+ ferrous (or Iron II)Fe 2+ ferric (or Iron III)Fe 3+ ferric (or Iron III)Fe 3+ silver Ag + silver Ag + zinc Zn 2+ zinc Zn 2+

9. Monatomic Non-Metal Ions bromide Br – bromide Br – chloride Cl – chloride Cl – fluoride F – fluoride F – iodideI - iodideI - oxide O 2– oxide O 2– sulfide S 2– sulfide S 2– nitrideN 3- nitrideN 3-