Naming Chemical Compounds and Writing Formulae (c) McGraw Hill Ryerson 2007

3.2 Names & Formulas of Ionic Compounds Rules for naming ionic compounds: Positive ion (metal) is always first Negative ion (non-metal) is always second Non-metal ion’s name ends with the suffix “-ide” Practice: BaCl2 NaF Al2O3 K2S CaO See page 85

Ionic Chemical Formulas In an ionic compound, the positive charges balance the negative charges. You need to determine the smallest whole number ratio of positive to negative ions. See page 87 (c) McGraw Hill Ryerson 2007

Practice: BaCl2 NaF Al2O3 K2S CaO Ba3P2 Na2O BeS

Rules for writing ionic formulae: Identify each ion and its charge. (Metal first then non-metal) Determine the smallest number of charges needed to balance out the +’s and –’s Write this ratio in subscript form (Note: do not write ones) Ex. 1: zinc nitride Ex. 2: aluminum chloride

Short-cut: “Swap and Drop” Write each element’s symbol with their charges The charge (without the sign) of one ion becomes the subscript of the other ion. Reduce subscripts to the smallest whole numbers that keep the ration of ions.

Why this works: Consider beryllium fluoride:

Practice! Na and Cl Ba and F K and S Al and I Ag and O

Multivalent Metal Compounds Many metals are multivalent, meaning the metals form two or more different positive ions with different charges For ex., the atom iron forms two ions Fe2+ and Fe3+ Use roman numerals to distinguish between the ions. For ex., Fe3+ would be named “iron(III)” See page 88 (c) McGraw Hill Ryerson 2007

Know your Roman numerals! (c) McGraw Hill Ryerson 2007

Writing Multivalent Formulas Same rules as regular ionic compounds but you don’t have to look up the charges (a.k.a. combining capacity) on the metal – just look at the roman numeral! Practice: Copper (I) chloride Copper (II) chloride Cobalt (III) oxide Manganese (IV) sulphide See page 89 (c) McGraw Hill Ryerson 2007

Multivalent Compound Names Steps to writing multivalent compound names are as follows: Identify the metal and verify it forms more than one ion. Look at the formula and reverse “swap & drop”. Check the periodic table to see what the charge on the non-metal & to make sure the ratio hasn’t been reduced. For example: Fe2O3 See page 90 (c) McGraw Hill Ryerson 2007

Writing the Formula of Polyatomic Ion (PAI) Compounds Write the ions and their charges. “Swap and drop”. Reduce if necessary For example: Ammonium sulphide Magnesium nitrate See page 91 (c) McGraw Hill Ryerson 2007

Writing the Names of Polyatomic Ion (PAI) Compounds Verify a polyatomic atom is present. Name the positive ion and decide if a roman numeral is necessary. Name the negative ion and if it is a polyatomic ion, do NOT change the ending on the name. For example: Na3PO4 (NH4)2CO3 (c) McGraw Hill Ryerson 2007

Practice: Write the formula for: sodium nitrate potassium acetate aluminum sulfate lithium chlorate magnesium nitrate

2. Write the name: KNO3 Ba(OH)2 Li2CO3 Fe2(SO4)3 NH4ClO3

Writing and Naming Covalent Compounds Uses Greek prefixes to show how many atoms of each element are present Last vowel of the prefix is dropped when the second element begins with a vowel Mono is omitted on the metal Do NOT use the charges on the periodic table!! Remember: Covalent compounds SHARE electrons so NO ions are formed. It is ions that possess the charges. For example: dinitrogen trioxide N2O3 carbon tetrafluoride CF4

Know your prefixes! Number Prefix 1 Mono- 2 Di- 3 Tri- 4 Tetra- 5 Penta- Number Prefix 6 Hexa- 7 Hepta- 8 Octa- 9 Nona- 10 Deca-

Practice: CO CO2 SO2 N2O CCl4 P2O5 PCl3 PBr5 Take the Section 3.2 Quiz