Polyatomic Ions

SNC2D

POLYATOMIC IONS

● Polyatomic ions are groups of atoms that tend to stay together and carry an overall ionic charge

● The ion is typically held together with covalent bonds

● The polyatomic ion is capable of bonding with other ions

POLYATOMIC IONS TO KNOW

● Below is the list of polyatomic ions you need know

● The list is from the periodic table for SNC2DI

WRITING FORMULAS WITH POLYATOMIC IONS

1. Write the symbol for the cation first and the anion second

2. Write the combining capacity for each element over each of the ions (for polyatomic ions this is the same as the ionic charge)

3. Use “cross over” method and reduce numbers to lowest ratio without changing the formula for the ion

Na + SO42- →

Na2SO4 Al + OH- → Al(OH)3

NH41+ + NO3

- → NH4NO3

NAMING COMPOUNDS CONTAINING POLYATOMIC IONS

● Name of the metal first

● Name of the polyatomic ion second

● Polyatomic ions usually end in “ate”

Na2SO4 → sodium sulphateAl(OH)3 → aluminum hydroxideNH4NO3 → ammonium nitrate

OXYACIDS

● When hydrogen bonds to many of the polyatomic ions that contain oxygen, oxyacids form:

● nitrate (NO3-)

→ nitric acid (HNO3)

● phosphate (PO43-)

→ phosphoric acid (H3PO4)