Aim: How do we name binary ionic compounds given the chemical formula

Binary Compound Binary Compounds are composed of two elements bonded together One Metal, and One Nonmetal for Ionic Compound

What are chemical formulas A chemical formula tells us the number of atoms of each element in a compound. It contains the symbols of the atoms of the elements present in the compound, as well as how many there are for each element in the form of subscripts.

Formula Units Ionic compounds do not exist as discrete units, but as collections of positively and negatively charged ions arranged in repeating patterns.

Formula Units The chemical formula of an ionic compound refers to a ratio known as a formula unit. A formula unit is the lowest whole-number ratio of ions in an ionic compound.

Formula Units For sodium chloride, the lowest whole-number ratio of the ions is 1:1 (one Na+ ion to each Cl– ion). The formula unit for sodium chloride is NaCl. Although ionic charges are used to derive the correct formula, they are not shown when you write the formula unit of the compound.

Naming Ionic Compounds with Two Elements To name a compound that contains two elements, identify the cation (+ ion) and anion (- ion). name the cation first followed by the name of the anion.

Naming Ionic compounds with metals that have only one oxidation state

Names of Some Common Ions Naming nonmetal ions: element stem name + “ide” + ion Naming metal ions with one oxidation state: Element name + ion

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

Examples of Ionic Compounds with Two Elements Formula Ions Name cation anion 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

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

Transition Metals form Positive Ions Most transition metals and Group 4(14) metals form 2 or more positive ions. Zn2+, Ag+, and Cd2+ form only one ion.

Metals that form more than One Cation The name of metals with two or more positive ions (cations) use a Roman numeral to identify ionic charge. Lead Pb2+ lead(II) Pb4+ lead(IV) Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Naming Ionic Compounds with Variable Charge Metals

Naming Variable Charge Metals Transition metals with two or more different ions use a Roman numeral after the name of the metal to indicate ionic charge.

Naming FeCl2 To name FeCl2 1. Determine the charge of the cation using the charge of the anion (Cl-). Fe ion + 2 Cl- = Fe ion + 2 (-1) = 0 Fe ion = 2+ 2. Name the cation by the element name and add a Roman numeral in parenthesis to show its charge. Fe2+ = iron(II) 3. Write the anion with an ide ending. FeCl2 = iron(II) chloride

Naming Cr2O3 To name Cr2O3 1. Determine the charge of cation from the anion (O2-). 2 Cr ions + 3 O2- = 0 2 Cr ions + 3(2-) = 0 2 Cr ions - 6 = 0 2 Cr ions = +6 Cr ion = 3+ = Cr3+ 2. Name the cation by the element name and add a Roman numeral in parenthesis to show its charge. Cr3+ = chromium(III) 3. Write the anion with an ide ending. chromium(III) oxide = Cr2O3

Practice: Given the formula determine the chemical name Chemical Formula Cation (+) ion (Metal ion) Anions (-) ions (Nonmetal ion) Chemical Name MgCl2 KCl AgF FeO PbI4

Summary Steps to naming Binary Ionic Compounds 1. Determine if the metal is a transition metal. 2. If Transition Metal, Determine the proper oxidation number to use. (Use nonmetal to help you determine) 3. Write down the name of the metal. (use roman numerals to show oxidation state for transition metals) 4. Write the name of the non-metal, changing the ending to ide Ex: Oxide, Fluoride, Bromide, Chloride, Nitride Examples NaF2 CuO Al2O3 Cu2O SnF2

Predicting Formulas of Ionic Compounds Sample Problem 7.1 Predicting Formulas of Ionic Compounds Use electron dot structures to predict the formulas of the ionic compounds formed from the following elements: a. potassium and oxygen b. magnesium and nitrogen

Analyze Identify the relevant concepts. Sample Problem 7.1 Analyze Identify the relevant concepts. 1 Atoms of metals lose valence electrons when forming an ionic compound. Atoms of nonmetals gain electrons. Enough atoms of each element must be used in the formula so that electrons lost equal electrons gained.

Solve Apply the concepts to this problem. Sample Problem 7.1 Solve Apply the concepts to this problem. 2 a. Start with the atoms. • • • K and O • • • •

Solve Apply the concepts to this problem. Sample Problem 7.1 Solve Apply the concepts to this problem. 2 a. In order to have a completely filled valence shell, the oxygen atom must gain two electrons. These electrons come from two potassium atoms, each of which loses one electron. K • • • O + K+ 2–

Solve Apply the concepts to this problem. Sample Problem 7.1 Solve Apply the concepts to this problem. 2 a. Express the electron dot structure as a formula. The formula of the compound formed is K2O (potassium oxide).

Solve Apply the concepts to this problem. Sample Problem 7.1 Solve Apply the concepts to this problem. 2 b. Start with the atoms. Mg and N • • •

Solve Apply the concepts to this problem. Sample Problem 7.1 Solve Apply the concepts to this problem. 2 b. Each nitrogen atom needs three electrons to have an octet, but each magnesium atom can lose only two electrons. Three magnesium atoms are needed for every two nitrogen atoms. • • • N 3– + Mg2+ Mg

Solve Apply the concepts to this problem. Sample Problem 7.1 Solve Apply the concepts to this problem. 2 b. Express the electron dot structure as a formula. The formula of the compound formed is Mg3N2 (magnesium nitride).

Use electron dot structures to determine the formula of the ionic compound formed when calcium reacts with fluorine.

Guide to Writing Formulas from the Name

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

Writing Formulas Write a formula for iron(III) chloride. 1. Identify the cation and anion. iron (III) = Fe3+ (III = charge of 3+) chloride = Cl− 2. Balance the charges. Fe3+ Cl− Cl− = (3+) + 3(1-) = 0 Cl− 3. 1 Fe3+ and 3 Cl− = FeCl3

Example: Aluminum Chloride Predicting Chemical Formula of Ionic Compounds Criss-Cross Rule Example: Aluminum Chloride Step 1: write out name with space Al Cl 3+ 1- Step 2: write symbols & charge of elements Al Cl Step 3: 1 3 criss-cross charges as subscripts Step 4: AlCl 3 combine as formula unit (“1” is never shown)

Example: Aluminum Chloride Criss-Cross Rule Example: Aluminum Chloride Step 1: Aluminum Chloride Step 2: Al3+ Cl1- Step 3: Al Cl 1 3 Step 4: AlCl 3

Example: Aluminum Oxide Criss-Cross Rule Example: Aluminum Oxide Step 1: Aluminum Oxide Step 2: Al3+ O2- Step 3: Al O 2 3 Step 4: Al2O3

Example: Magnesium Oxide Criss-Cross Rule Example: Magnesium Oxide Step 1: Magnesium Oxide Step 2: Mg2+ O2- Step 3: Mg O 2 2 Step 4: Mg2O2 Step 5: MgO

Practice Using Criss-Cross Method to Predict Ionic Formulas Predict the formulas of the ionic compounds formed form the following elements. Potassium and oxygen Magnesium and nitrogen K+1 O-2 K2O Mg+2 N-3 Mg3N2

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

Summary Steps to writing formulas of binary ionic compounds given the name 1. Write down the Chemical Symbols for each element 2. Determine if the metal is a transition metal. (If a roman numeral is used, it is a transition metal) 3. Using oxidation numbers, determine how many of each element are needed. 4. Write the final formula Ex: Aluminum nitride Aluminum oxide Gold (I) oxide