3/25/25, 9:25 PM Nomenclature for Binary Ionic Compounds General Chemistry 1 (Open + Free) (/jcourse/lms/students/syllabus.do? (/jcourse/workbook/activity/page? context=182898020a0001dc46062c13c9826f07) section=18287eda0a0001dc64aada34eee27b78) 35 (/jcourse/wo context=182 - [ SIGN IN ] (/JCOURSE/WEBUI/WELCOME.DO) () Unit 1 - Foundations of Chemistry This course is not led by an instructor Search Module 5 | (/jcourse/webui/syllabus/module.do? context=182897f70a0001dc082b35a5ec6dbdff) Nomenclature for Binary Ionic Compounds Learning Objectives Write chemical formulas for compounds. Name chemical compounds. In every ionic compound, the total number of positive charges of the cations equals the total number of negative charges of the anions. Thus, ionic compounds are electrically neutral overall, even though they contain positive and negative ions. We can use this observation to help us write the formula of an ionic compound. The formula of an ionic compound must have a ratio of ions such that the numbers of positive and negative charges are equal. A binary ionic compound consists of a monatomic (formed from one atom) cation and a monatomic anion. Note that the ending of the names of monatomic anions are changed to -ide. For example, sulfide is an ion of sulfur and phosphide is an ion of phosphorus. Writing a Chemical Formula for Binary Ionic Compounds 1. Identify the cation and anion and their charges. https://oli.cmu.edu/jcourse/workbook/activity/page?context=182898030a0001dc7b2b04f39aa4ef93 1/8 3/25/25, 9:25 PM Nomenclature for Binary Ionic Compounds 2. Combine the ions in the smallest whole number ratio such that the total number of positive charges is equal to the total number of negative charges. 3. Write the chemical formula that reflects this ratio. (/jcourse/workbook/activity/page? context=182898020a0001dc46062c13c9826f07) (/jcourse/wo context=182 Example Write the chemical formula for potassium sulfide. Determine the ionic charges. Referring to the periodic table, we see that potassium will form a 1+ ion and sulfur will form a 2- ion, as illustrated in the diagrams below. Combine in a ratio that results in a neutral compound. In order to obtain a neutral compound 2 potassium ions must combine with 1 sulfur ion. Resulting in a chemical formula of: K S 2 Criss-Cross Method of Writing Chemical Formulas A convenient method to write chemical formulas is by using the criss-cross method. In this method the value of the ionic charge for the cation becomes the subscript of the anion in the chemical formula and the value of the ionic charge of the anion becomes the subscript of the cation in the chemical formula. Looking at the previous example we can see how the criss-cross method works. https://oli.cmu.edu/jcourse/workbook/activity/page?context=182898030a0001dc7b2b04f39aa4ef93 2/8 3/25/25, 9:25 PM Nomenclature for Binary Ionic Compounds (/jcourse/workbook/activity/page? context=182898020a0001dc46062c13c9826f07) (/jcourse/wo context=182 Like the previous method, the result is K2 S. One thing to remember with the criss-cross method is that the ratio of ions in a chemical formula of an ionic compound must always be in the smallest whole number ratio. Example Write the chemical formula for magnesium oxide. Determine the ionic charges. Use the criss-cross method. Notice the result of the criss-cross method results in: Mg O 2 2 This 2:2 ratio of ions is reduced to 1:1, resulting in the formula: MgO Learn By Doing What is the chemical formula for magnesium bromide? https://oli.cmu.edu/jcourse/workbook/activity/page?context=182898030a0001dc7b2b04f39aa4ef93 3/8 3/25/25, 9:25 PM Nomenclature for Binary Ionic Compounds Mg2 Br Mg2 Br2 (/jcourse/workbook/activity/page? context=182898020a0001dc46062c13c9826f07) MgBr2 (/jcourse/wo context=182 MgBr Correct. Magnesium will form a 2+ ion and bromine will from a 1- ion. (javascript();) What is the chemical formula for calcium nitride? CaN Ca2 N Ca3 N2 Ca2 N3 Correct. Calcium will form a 2+ ion and nitrogen will from a 3- ion. This 3:2 ratio of calcium to nitride will result in a neutral compound. (javascript();) What is the chemical formula for sodium oxide? Na2 O Na2 O3 NaO NaO2 Correct. Sodium will form a 1+ ion and oxygen will form a 2- ion. This 2:1 ratio of sodium to oxide will result in a neutral compound. (javascript();) Reset this Activity https://oli.cmu.edu/jcourse/workbook/activity/page?context=182898030a0001dc7b2b04f39aa4ef93 4/8 3/25/25, 9:25 PM Nomenclature for Binary Ionic Compounds Naming Binary Ionic Compounds Given the name of a binary ionic compound you can derive the formula and given the formula you (/jcourse/workbook/activity/page? can name the compound. context=182898020a0001dc46062c13c9826f07) (/jcourse/wo context=182 Naming Binary Ionic Compounds 1. Name the cation first. If the cation is monatomic, the name is the same as the element name. 2. Name the anion second. If the anion is monatomic, change the ending of the element name to -ide. 3. Add roman numeral that indicates the charge of the ion for cations that can have multiple charges. Example Name the compound Li P. 3 Name the cation. The cation is lithium. Name the anion, change its ending to -ide. The anion is the phosphorus ion, which we change the name to phosphide. The name of the compound is: lithium phosphide Learn By Doing Name the following compounds: Al2 S3 aluminum sulfide CsBr cesium bromide (javascript();) (javascript();) https://oli.cmu.edu/jcourse/workbook/activity/page?context=182898030a0001dc7b2b04f39aa4ef93 5/8 3/25/25, 9:25 PM Nomenclature for Binary Ionic Compounds Correct. Name the cation and change the ending of the anion to -ide. Correct. Name the cation and change the ending of the anion to -ide. (/jcourse/workbook/activity/page? context=182898020a0001dc46062c13c9826f07) (/jcourse/wo context=182 Reset this Activity Naming Ionic Compounds with Multiple Charge Cations In all of the examples we have looked at so far the cation in the formula can only form one ion. For example, when the calcium atom forms an ion, it is always Ca2+ or when potassium forms an ion it is always K+. However some of the transition metals can form different ions. For example lead can form ion Pb2+ and Pb4+. So when it combines with chlorine the result may be PbCl2 or PbCl4 . When we write the name for each of these formulas we need to indicate whether the compound is formed from the Pb2+ and Pb4+ ion. We do this using roman numerals. Where the roman numeral indicates the charge of the ion in the formula. Formula Cation in the Compound Name of the Compound PbCl2 Pb2+ lead(II) chloride PbCl4 Pb4+ lead(IV) chloride Note that not all transition metals can form multiple cations. Here is a list of the most common. Formula Cation in the Compound Chromium(II) Cr2+ Chromium(III) Cr3+ Manganese(II) Mn2+ Manganese(III) Mn3+ Iron(II) Fe2+ Iron(III) Fe3+ Cobalt(II) Co2+ Cobalt(III) Co3+ https://oli.cmu.edu/jcourse/workbook/activity/page?context=182898030a0001dc7b2b04f39aa4ef93 6/8 3/25/25, 9:25 PM Nomenclature for Binary Ionic Compounds Copper(I) Cu+ Copper(II) Cu2+ (/jcourse/workbook/activity/page? context=182898020a0001dc46062c13c9826f07) Mercury(I) Hg2 2+ Mercury(II) Hg2+ Tin(II) Sn2+ Tin(IV) Sn4+ Lead(II) Pb2+ Lead(IV) Pb4+ (/jcourse/wo context=182 It is also worth noting that the following metals always form the same ion. Silver always forms Ag+. Cadmium always forms Cd2+. Zinc always forms Zn2+. Gallium always forms Ga3+. Aluminum always forms Al3+. Learn By Doing Name the following compounds. (Be sure to spell correctly and do not add any punctuation to the answer box. Do not add a space between the name of the cation and the roman numeral. Put parentheses around the roman numeral.) For example: SnCl2 should be entered as tin(II) chloride. (javascript();) FeS Iron (II) sulfide (javascript();) SnO Tin (IV) Oxide (javascript();) Cu N Copper (II) Nitride (javascript();) CrCl3 chromium (III) chlorid 2 3 2 The chromium atom can form a 2+ ion or a 3+ ion. Tin can form +2 and +4 ions. Oxygen forms a -2 ion. The copper atom can form a 1+ ion or a 2+ ion. Correct. The Cr3+ ion would produce the compound CrCl3 . https://oli.cmu.edu/jcourse/workbook/activity/page?context=182898030a0001dc7b2b04f39aa4ef93 7/8 3/25/25, 9:25 PM Nomenclature for Binary Ionic Compounds Correct. The Fe2+ ion would produce the compound FeS. Correct. The Sn4+ ion combining with O2- would produce the compound SnO2 . 2+ Correct. The Cu ion would produce the compound Cu3 N2 . (/jcourse/workbook/activity/page? context=182898020a0001dc46062c13c9826f07) (/jcourse/wo context=182 Reset this Activity Adapted from Openstax Chemistry (https://cnx.org/contents/havxkyvS@9.422:b39avmGq@29/Preface) under Creative Commons Attribution 4.0 License. (https://creativecommons.org/licenses/by/4.0/) Download for free at http://cnx.org/contents/85abf193-2bd2-4908-8563-90b8a7ac8df6@9.312. (http://cnx.org/contents/85abf193-2bd2-4908-8563-90b8a7ac8df6@9.312) (http://creativecommons.org/licenses/by-nc-sa/4.0/)Unless otherwise noted this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 Unported License (http://creativecommons.org/licenses/by-nc-sa/4.0/) . Open Learning Initiative (/) https://oli.cmu.edu/jcourse/workbook/activity/page?context=182898030a0001dc7b2b04f39aa4ef93 8/8
