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

OH -1 NO 3 -1 ClO 3 -1 CO 3 -2 SO 4 -2 PO 4 -3 NO 2 -1 SO 3 -1 CN -1 HCO 3 -1 C 2 H 3 O 2 -1 ClO 4 -1 ClO 2 -1 ClO -1 NH 4 +1

Symbol

Hydroxide Nitrate Chlorate Carbonate Sulfate Phosphate Nitrite Sulfite Cyanide Bicarbonate Acetate Perchlorate Chlorite Hypochlorite Ammonium

Practice Identifying Polyatomic Ions

Example:

Identify and name the polyatomic ion in each compound NaNO NH 4 Cl 3 Ca(OH) 2 (NH 4 ) 3 PO 4 K 2 CO 3 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 - Al 2 (SO 4 ) 3 Three SO 4 -2 groups NOT SO 43 -2

Practice Identifying Polyatomic Ions

Example:

Identify and name the polyatomic ion in each compound NaNO 3 NH 4 Cl Ca(OH) 2 (NH 4 ) 3 PO 4 K 2 CO 3 Nitrate Ammonium Hydroxide Ammonium & phosphate Carbonate

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 NH 4  Name the anion write down the name ammonium  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

NaNO

3

Example #1

“Sodium” Cation

NaNO

3 Polyatomic Anion “Nitrate”

Sodium Nitrate

Example #2

K

2

SO

4

Example #2

“Potassium” Cation

K

2

SO

4 Polyatomic Anion “sulfate”

Potassium sulfate

Example #3

Cu(OH)

2

Example #3

“Copper” A Multivalent Metal Cation

Cu(OH)

2

Two OH -1 groups provide a total charge of -2. The Copper has to be +2 to balance this charge.

Polyatomic Anion “hydroxide”

Copper (II) hydroxide

Example #4

(NH

4

)

2

S

Example #4

“Ammonium” Polyatomic Cation

(NH

4

)

2

S

Anion “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 CO 3 -2

Example #1

Na +1 Cation Sodium carbonate Polyatomic Anion CO 3 -2

Na

2

CO

3 Na +1 CO 3 2 +1 + -2 = -1 Na +1 Na +1 CO 3 2 +1 + 1 + -2 = 0 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 NO 3 -1

Example #2

Mg +2 Cation

Mg +2 NO 3 +2 + -1 =+ 1

Magnesium nitrate

Mg +2 NO 3 NO 3 -

Polyatomic Anion NO 3 -1

+2 + -1 + -1 = 0 The subscript “2” is used to show that 2 anions are needed.

Mg(NO

3

)

2 Use parenthesis when adding subscripts to polyatomic ions