POLYATOMIC IONS

Poly - many Atomic - atoms Polyatomic ion - a many atom ion - a group of atoms tightly held together that acts like a single ion All are negative except for NH4+ (ammonium), the only positive polyatomic ion

Writing Names The metal is written as before: If a single valent metal, just write the name If it is a multivalent metal, you must include the roman numeral indicating the charge. Ammonium is single valent. If ammonium is the positive ion, do NOT use a roman numeral A negative polyatomic ion is written as is with out change

EXAMPLES KNO3 Potassium is single valent, so no roman numerals Potassium nitrate

FeSO4 Iron is multi Valent, so we must find its ionic charge Fe2+ SO42- Iron (II) sulphate

Al(ClO4)3 Aluminum perchlorate

Fe2(CO3)3 Iron is multivalent Fe+3 CO32- CO32- ___________________ +6 -6 Iron (III) carbonate

NH4Br Ammonium Bromide (NH4)3PO4 Ammonium phosphate

WRITING FORMULA Done the same as before except: If there is more than 1 of the polyatomic ion, it MUST be in brackets If there is only one of the polyatomic ion, it MUST NOT be in brackets DO NOT CHANGE THE FORMULA

EXAMPLES Barium sulphite Ba+2 SO32- Just need one of each BaSO3

Ammonium carbonate NH4+ CO32- NH4+ ______________________ +2 -2 (NH4)2CO3

Lead ( II ) hydroxide Pb+2 OH- OH- __________________ +2 -2 Pb(OH)2

Cobalt (II) phosphate Co+2 PO43- Co+2 PO43- Co+2 ___________________ +6 -6 Co3(PO4)2