Polyatomic Ionic Compounds

Definition Polyatomic Ion- more than one atom that together have a charge Polyatomic Ionic Compound- compound containing at least one polyatomic ion + Cation - Polyatomic Anion Polyatomic Ionic Compound

Common Polyatomics Name Symbol OH-1 Hydroxide NO3-1 Nitrate ClO3-1 Chlorate CO3-2 Carbonate SO4-2 Sulfate PO4-3 Phosphate NO2-1 Nitrite SO3-1 Sulfite CN-1 Cyanide HCO3-1 Bicarbonate C2H3O2-1 Acetate ClO4-1 Perchlorate ClO2-1 Chlorite ClO-1 Hypochlorite NH4+1 Ammonium

Practice Identifying Polyatomic Ions NaNO3 NH4Cl Ca(OH)2 (NH4)3PO4 K2CO3 Example: Identify and name the polyatomic ion in each compound Note: Parenthesis are only used on POLY’s and only when we need more than one. You can’t change the subscript on the poly. Example - Al2(SO4)3 Three SO4-2 groups NOT SO43-2

Practice Identifying Polyatomic Ions NaNO3 NH4Cl Ca(OH)2 (NH4)3PO4 K2CO3 Nitrate Ammonium Hydroxide Ammonium & phosphate Carbonate Example: Identify and name the polyatomic ion in each compound

Naming Polyatomic Ionic Compounds To name these compounds: Write the name of the cation If it is a metal just name the metal If it is a multivalent metal, name the metal and put a set of parenthesis after it If it is a NH4 write down the name ammonium Name the anion If the anion is a polyatomic ion, just name the polyatomic If the anion is a single non-metal element, write its name with the suffix “-ide” Determine the roman numeral if it is multivalent

Example #1 NaNO3

NaNO3 Example #1 Sodium Nitrate Cation Polyatomic Anion “Sodium”

Example #2 K2SO4

K2SO4 Example #2 Potassium sulfate Cation Polyatomic Anion “Potassium”

Example #3 Cu(OH)2

Cu(OH)2 Example #3 Copper (II) hydroxide Cation Polyatomic Anion “Copper” A Multivalent Metal Cation Two OH-1 groups provide a total charge of -2. The Copper has to be +2 to balance this charge. Cu(OH)2 Polyatomic Anion “hydroxide” Copper (II) hydroxide

Example #4 (NH4)2S

(NH4)2S Example #4 Ammonium sulfide Polyatomic Cation Anion “Ammonium” “sulfur” becomes “sulfide” Ammonium sulfide

Writing Formulas for Polyatomic Ionic Get out your Poly List!!!! To write these formulas: Write the symbol & charge of the cation & anion Add additional cations or anions to have a neutral compound. (We once again do this by balancing charge. Methods such as the Swap/Drop/Reduce or Lowest Common Multiple) Use subscripts to show the number of ions When using subscripts with a polyatomic ion, you must put the polyatomic ion in parenthesis.

Example #1 Sodium carbonate

Example #1 Na+1 Cation Sodium carbonate Polyatomic Anion CO3-2

Na2CO3 Example #1 Sodium carbonate Cation Polyatomic Anion Na+1 +1 + -2 = -1 Polyatomic Anion Na+1Na+1CO32- +1 + 1 + -2 = 0 CO3-2 Na2CO3 The subscript “2” is used to show that 2 cations are needed.

Example #2 Magnesium nitrate

Example #2 Mg+2 Cation Magnesium nitrate Polyatomic Anion NO3-1

Mg(NO3)2 Example #2 Magnesium nitrate Cation Polyatomic Anion Mg+2 +2 + -1 =+ 1 Magnesium nitrate Mg+2NO3- NO3- Polyatomic Anion +2 + -1 + -1 = 0 NO3-1 The subscript “2” is used to show that 2 anions are needed. Mg(NO3)2 Use parenthesis when adding subscripts to polyatomic ions