How to name ionic compounds with polyatomic ions

How to name ionic compounds with polyatomic ions

How to name ionic compounds with polyatomic ions
SNC2D1
NaCl (table salt) enhances flavour and extends shelf life
Sodium phosphate is a white solid, relatively stable, and an
electrolyte
 Chemical formula: Na3PO4.
 Sodium, Na = cation
 Phosphate, (PO4)3- = anion
This is an example of a
POLYATOMIC ION
Polyatomic Ions



“poly” means “many”
consists of a stable group of several atoms acting together as a single charged particle
The ionic charge of a polyatomic ion is shared over the entire ion rather than being on just
one atom
The phosphate ion is made up of 4 oxygen atoms bonded to a central
phosphorus atom = (PO4)3-
Naming Compounds with Polyatomic Ions
Example 1: Write the name of the compound Na2CO3
Step 1: Write the name of the metal and check whether is has more than one ionic charge
Sodium (always has a charge of +1)
Step 2: Recognize and name the polyatomic ion
CO3 is the carbonate ion
Step 3: Write the name of the compound
The name of Na2CO3 is Sodium carbonate
Example 2: What is the name of Ca(OH)2?
Step 1: Calcium (always has a charge of +2)
Step 2: (OH) is the hydroxide ion
Step 3: The name of Ca(OH)2 is Calcium hydroxide
Example 3: What is the name of Fe(NO3)3?
Step 1: Iron (has a charge of +2 or +3)
Step 2: Determine the ionic charge of iron!
Fex + 3(NO3)1- = 0
x + 3(-1) = 0
x + (-3) = 0
x = +3
Therefore, the charge on the Fe ion is +3
Step 3: (NO3) is the nitrate ion
Step 4: The name of Fe(NO3)3 is Iron (III) nitrate
Writing chemical formulas involving polyatomic ions
Example 1: Write the formula for sodium phosphate
Step 1: Write the symbols and ionic charges above each symbol
Step 2: Determine how many of each ions are required to give a total charge of zero OR use
the criss-cross method
Step 3: Write the chemical formula using subscripts
Method #1
Na1+
+
(PO4)3___(+1) + ___(-3) = 0
3 (+1) + 1 (-3) = 0
(+3) + (-3) = 0
Chemical formula: Na3(PO4)
Criss-Cross Method
(Na)1+ (PO4)3Na3
(PO4)1
Chemical formula: Na3(PO4)
Example 2: What is the chemical formula for copper (II) nitrate?
Method #1
Criss-Cross Method
Cu2+
+
(NO3)1___(+2) + ___(-1) = 0
1 (+2) + 2 (-1) = 0
(+2) + (-2) = 0
Chemical formula: Cu(NO3)2
(Cu)2+ (NO3)1Cu1
(NO3)2
Chemical formula: Cu(NO3)2
Example 3: What is the chemical formula for ammonium carbonate?
Method #1
Criss-Cross Method
(NH4)1+ +
(CO3)2___(+1) + ___(-2) = 0
2 (+1) + 1 (-2) = 0
(+2) + (-2) = 0
Chemical formula: (NH4)2(CO3)
(NH4)1+
(CO3)2-
(NH4)2
(CO3)1
Chemical formula: (NH4)2(CO3)
Oxyacids
 A special group of polyatomic ions
 Formed when hydrogen combines with polyatomic ions that contain oxygen
 In these compounds, hydrogen has an ionic charge of +1
 See Table 3 on page 198 for examples of common oxyacids