Names & Formulas of Compounds #3 Naming and Writing Ionic Formulas Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

What is a binary ionic compound? Binary means “two” A binary ionic compound is made of 2 elements only…always a metal first and a nonmetal last

Some Ionic Compounds with Two Elements Formula Ions Name NaCl Na+ Cl- sodium chloride K2S K+ S2- potassium sulfide MgO Mg2+ O2- magnesium oxide CaI2 Ca2+ I- calcium iodide Al2O3 Al3+ O2- aluminum oxide

What you will do… If given the formula, you will have to determine the correct name If given the name, you will have to determine the correct formula

Get your Periodic Table out and look at it… Elements in groups 1, 2, and 13-17 have fixed or set charges when they form ions…you should already have these marked on your table (Group 1 is +1, etc…) But most transition metals (groups 3-12) AND tin (Sn) and lead (Pb) form multiple ions because of a varying valence Silver (Ag), Cadmium (Cd), and Zinc (Zn) are the only transition metals that have fixed charges…you must memorize this!!!!!!

OUTLINE Silver, Cadmium, & Zinc on your table…write in their charges…OUTLINE Tin & Lead on your table

Metals with varying charges Because most of the metals in groups 3 to 12 and Sn & Pb have multiple charges, when you name them in a compound you must include a Roman Numeral after their name to indicate which ion it is…Pb+2 is called Lead II…Pb+4 is called Lead IV Remember, Ag, Cd, & Zn have only one charge…they will NEVER need Roman Numerals with their names.

Over groups 3-12 write "need roman numerals " Over groups 3-12 write "need roman numerals ". Under Sn & Pb, write "need roman numerals". Above Ag, Cd, & Zn write "do not need roman numerals". You can abbreviate RN for roman numerals…

Another ion to watch for… Mercury forms two ions Mercury II is just Hg+2 Mercury I is odd…2 mercury I's will always go in pairs in a compound, so even though they have a +1 charge each, because there are two of them you will use them like this: Hg2+2

Writing Formulas when given the name of the compound— STEP 1. Identify the cation . Cations are metals. Write down the metal ion and the charge it normally has according to the periodic table. If it has a Roman numeral, that is its charge. STEP 2. Identify the anion. Anions are nonmetals. Write down the ion and its normal charge. STEP 3. Balance the charges. Remember that compounds have no charges!!

Writing Formulas: Example Write the formula of potassium sulfide. STEP 1 Identify the cation and anion. potassium = K+ sulfide = S2− STEP 2. Balance the charges. K+ S2− K+ 2(1+) + 2(1-) = 0 STEP 3. 2 K+ and 1 S2− = K2S

Learning Check The correct formula for each of the following is: A. Copper (I) nitride 1) CuN 2) CuN3 3) Cu3N B. Lead (IV) oxide 1) PbO2 2) PbO 3) Pb2O4

Solution The correct formula is A. Copper (I) nitride 3) Cu3N Need 3Cu+ and N3- B. Lead (IV) oxide 1) PbO2 Need Pb4+ and 2O2-

Naming of Binary Ionic Compounds To NAME a binary ionic compound 1. Look at the METAL a. If it's a Group 1, Group 2, or Group 13 metal, OR Ag, Zn, or Cd, just use the name of the metal. b. If it's a TRANSITION metal from groups 3-12, OR tin (Sn) or lead (Pb) it will need a roman numeral! 2. The negative nonmetal ion (second ion) is named by changing the end of the element name to –ide. EX: Chlorine becomes chloride Bromine becomes bromide

Names of Some Common Ions Table 5.3 3A (13) Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Learning Check--practice Complete the names of the following ions: Ba2+ Al3+ K+ _________ __________ _________ N3 O2 F _________ __________ _________ P3 S2 Cl

Solution barium aluminum potassium N3 O2 F nitride oxide fluoride Ba2+ Al3+ K+ barium aluminum potassium N3 O2 F nitride oxide fluoride P3 S2 Cl phosphide sulfide chloride

Learning Check Write the names of the following compounds: 1) CaO ___________ 2) KBr ___________ 3) Al2O3 ___________ 4) MgCl2 ___________

Solution Write the names of the following compounds: 1) CaO calcium oxide 2) KBr potassium bromide 3) Al2O3 aluminum oxide 4) MgCl2 magnesium chloride

Naming a compound that has a transition metal in it… To name Cr2O3, or any other compound that contains a metal with a variable charge Always start with the anion. It has a fixed charge. O is always (2-) and there are 3 of them. 3 x (-2) = -6. Therefore, the metal portion must have a total charge of +6 to balance the compound 2. Divide the + charge of metal by the number of metal ions: +6 ÷ 2 = +3 3. Name the cation by the element name and use a Roman numeral in parenthesis to show its charge. Cr3+ = chromium(III) 4. Write the name of the anion with -ide ending. chromium (III) oxide = Cr2O3

Learning Check Select the correct name for each. A. Fe2S3 1) iron sulfide 2) iron(II) sulfide 3) iron (III) sulfide B. CuO (Careful! Remember oxygen’s charge!) 1) copper oxide 2) copper(I) oxide 3) copper (II) oxide

Solution Select the correct name for each. A. Fe2S3 3) iron (III) sulfide Fe3+ S2- B. CuO 3) copper (II) oxide Cu2+ O2- Note: Because Cu and O both have the same charge, the formula is reduced to a 1:1 ratio Cu2O2 = CuO