Ionic Bonding: Polyatomic Ions & Roman Numerals

Ex: (NO3)1- Polyatomic Ions Ionic compounds with polyatomic ions – Polyatomic Ion – a charged group of covalently bonded atoms that stay bonded together during chemical reactions Ex: (NO3)1-

Polyatomic Ions The STAAR Chart contains the most common Polyatomic Ions You have the list – Keep it! Also, these are not ALL the polyatomic ions that exist, but the ones you will see in this course.

Writing Formulas with Polyatomic Ions Example #1: Ammonium chloride NH4Cl NH4 Cl +1 1– Example #2: Copper (II) sulfate CuSO Cu+2 SO4 2– 4 NEVER drop the polyatomic ion’s original subscripts!!

Writing Formulas with Polyatomic Ions When more than one of a particular polyatomic ion is present, parentheses are needed Parentheses go around the entire formula of the polyatomic ion with the NEW subscript outside parentheses – Subscript describes the number of polyatomic ions Example #3: Ammonium carbonate NH4 (NH4)2CO3 +1 CO3 2–

NH +1 SO 2– Sr+2 OH1– Ba+2 Fe+3 More Examples Ammonium sulfate 4 4 Strontium hydroxide Sr+2 OH1– Barium phosphate • (NH4)2SO4 Sr(OH)2 • Ba3(PO4)2 Ba+2 PO4 3– Iron (III) nitrite Fe(NO2)3 Fe+3 NO2 1–

Naming Ionic Compounds with Polyatomic Ions Ionic compound naming pattern NEVER change a polyatomic ion’s name. cation’s name + anion’s name Ex) NH4NO3 = ammonium nitrate Don’t forget to check if the CATION is a Transition Metal. If so, a Roman Numeral is required.

Examples Mg(OH)2 Magnesium hydroxide • (NH4)2S Ammonium sulfide Cu2SO4 FeSO3 NH4OH Magnesium hydroxide Ammonium sulfide Copper (I) sulfate Iron (II) sulfite Ammonium hydroxide

1 Sodium phosphate

2 Calcium carbonate

3 Potassium chloride

Sodium hypochlorite 4

5 Ammonium hydrogen carbonate

Writing Ionic Formulas with Roman Numerals Write ions with charges -The Transition metal’s charge IS the Roman numeral - Anions & Polyatomics have fixed charges so use the periodic table Cross and drop charges Reduce subscripts to the lowest whole number ratio Ex) Write the formula for lead(IV) oxide. Step 1 & 2: Pb4+ O–2 Step 3: Pb2O4 Step 4: PbO2 The charges of the ions balance each other so the overall charge is zero. Oxidation state will be written in the name as a Roman numeral Roman numerals 1-10 = I, II, III, IV, V, VI, VII, VIII, IX, X

Cu2+ S-2 Cu1+ S-2 Fe2+ N-3 Fe3+ Cl-1 More Examples Copper (II) sulfide Copper (I) sulfide Cu1+ S-2 Iron (II) nitride Fe2+ N-3 Iron (III) chloride Fe3+ Cl-1 Cu2S2 = CuS Cu2S Fe3N2 FeCl3

Naming Compounds with Roman Numerals Some metals have more than one oxidation state – In these cases, Roman numerals are used to denote the charge of the ion in the compound Binary ionic compound containing multiple oxidation state metal naming pattern metal’s name(Roman numeral) + non-metal’s stem + -ide = iron (II) fluoride Ex) FeF2

Fixed & Multiple Charged Metals In the table below – Metallic cations with a fixed charge – Common oxidation states of metals that form more than one cation

Metals with FIXED charges ►Metals with fixed charges will NOT have roman numerals next to their names. ►MEMORIZE the following elements AND their charges. Group 1 (1A) = +1 Group 2 (2A) = +2 Group 13 (3A) = +3 Group 14 (4A) = +4 (do not participate in Ionic bonds) Group 15 (5A) = –3 Group 16 (6A) = –2 Group 17 (7A) = –1 ►Zinc (Zn) = +2 ►Silver (Ag) = +1 ►Cadmium (Cd) = +2

Metals with MULTIPLE charges Only metals with multiple charges have a roman numeral in the name of the compound. The following metals WILL have roman numerals as a part of their name. All metals in groups 3-12 EXCEPT zinc (Zn), silver (Ag), and cadmium (Cd) Tin (Sn) = +2 or +4 Lead (Pb) = +2 or +4 Indium (In) = +1 or +3 Thallium (Tl) = +1 or +3

Naming Ionic Compounds with Roman Numerals  Example #1: What is the name of FeF2?  Finding the Roman Numeral for metals with Multiple Charges: Multiply the anion’s charge by the anion’s subscript. Then, drop the negative sign & divide by the cation’s subscript. That will give you the roman numeral.  Example Continued: FeF2 : First, –1 x 2 = –2 Iron’s oxidation number = +2 NAME OF FeF2 = Iron (II) fluoride Then, 2/1 = 2

Naming Ionic Compounds with Roman Numerals Example #2: What is the name for CuO? • CuO : First, –2 x 1 = –2 Then, 2/1 = 2 Copper’s oxidation number = +2 NAME OF CuO = Copper (II) oxide

More Examples Iron (III) chloride FeCl3 Cu3P PbO Copper (I) phosphide Zn3N2 MnO2 Copper (I) phosphide Lead (II) oxide Zinc nitride Manganese (IV) oxide