Covalent Formulas and Nomenclature Say Thanks to the Authors Click http://www.ck12.org/saythanks (No sign in required) To access a customizable version of this book, as well as other interactive content, visit www.ck12.org CK-12 Foundation is a non-profit organization with a mission to reduce the cost of textbook materials for the K-12 market both in the U.S. and worldwide. Using an open-content, web-based collaborative model termed the FlexBook®, CK-12 intends to pioneer the generation and distribution of high-quality educational content that will serve both as core text as well as provide an adaptive environment for learning, powered through the FlexBook Platform®. Copyright © 2014 CK-12 Foundation, www.ck12.org The names “CK-12” and “CK12” and associated logos and the terms “FlexBook®” and “FlexBook Platform®” (collectively “CK-12 Marks”) are trademarks and service marks of CK-12 Foundation and are protected by federal, state, and international laws. Any form of reproduction of this book in any format or medium, in whole or in sections must include the referral attribution link http://www.ck12.org/saythanks (placed in a visible location) in addition to the following terms. Except as otherwise noted, all CK-12 Content (including CK-12 Curriculum Material) is made available to Users in accordance with the Creative Commons Attribution-Non-Commercial 3.0 Unported (CC BY-NC 3.0) License (http://creativecommons.org/ licenses/by-nc/3.0/), as amended and updated by Creative Commons from time to time (the “CC License”), which is incorporated herein by this reference. Complete terms can be found at http://www.ck12.org/terms. Printed: October 12, 2014 www.ck12.org C HAPTER Chapter 1. Covalent Formulas and Nomenclature 1 Covalent Formulas and Nomenclature Lesson Objectives The student will: • list the Greek prefixes from 1 to 10. • provide the correct formulas for binary covalent compounds. • name binary covalent compounds using the IUPAC nomenclature system. Vocabulary • chemical nomenclature Introduction The systematic procedure for naming chemical compounds, or the chemical nomenclature, is different for different types of compounds. In the chapter “Ionic Bonds and Formulas,” we have discussed the procedures for naming binary ionic compounds, ionic compounds involving polyatomic ions, and ionic compounds involving metals with variable oxidation states. In this section, we will describe chemical nomenclature for covalently bonded compounds. Because of the large numbers of covalent compounds that may form between the same two elements, the nomenclature system for covalent compounds is somewhat different to the nomenclature system for ionic compounds. In naming ionic compounds, there is no need to indicate the number of atoms of each element in a formula because, for most cases, there is only one possible compound that can form from the ions present. When aluminum combines with sulfur, the only possible compound is aluminum sulfide, Al2 S3 . The only exception to this is a few metals with variable oxidation numbers, and these are handled by indicating the oxidation number of the metal with Roman numerals, such as in iron(II) chloride, FeCl2 . With covalent compounds, however, we have a very different situation. There are six different covalent compounds that can form between nitrogen and oxygen, and for two of them, nitrogen has the same oxidation number. Therefore, the Roman numeral system will not work. Instead, chemists devised a nomenclature system for covalent compounds that would indicate how many atoms of each element is present in a molecule of the compound. Greek Prefixes In naming binary covalent compounds, four rules apply: 1. The first element in the formula is named first using the normal name of the element. 2. The second element is named as if it were an anion. There are no ions in these compounds, but we use the “-ide” ending on the second element as if it were an anion. 3. Greek prefixes, shown in Table 1.1, are used for each element to indicate the number of atoms of that element present in the compound. 4. The prefix "mono-" is never used for naming the first element. For example, CO is called carbon monoxide, not monocarbon monoxide. 1 www.ck12.org TABLE 1.1: Greek Prefixes Prefix MonoDiTriTetraPentaHexaHeptaOctaNonaDeca- Number Indicated 1 2 3 4 5 6 7 8 9 10 Examples: N2 O NO NO2 N2 O3 N2 O4 N2 O5 SF6 CO2 P4 O10 P2 S5 dinitrogen monoxide nitrogen monoxide nitrogen dioxide dinitrogen trioxide dinitrogen tetroxide dinitrogen pentoxide sulfur hexafluoride carbon dioxide tetraphosphorus decaoxide diphosphorus pentasulfide Lesson Summary • Covalently bonded molecules use Greek prefixes in their nomenclature. Further Reading / Supplemental Links This website reviews the rules for naming binary covalent compounds and includes a quiz to test your understanding of these rules. • http://www.chem.purdue.edu/gchelp/nomenclature/covalent_2009.htm Review Questions 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 2 Name the compound CO. Name the compound PCl3 . Name the compound PCl5 . Name the compound N2 O3 . Name the compound BCl3 . Name the compound SF4 . Name the compound Cl2 O. Write the formula for the compound sulfur trioxide. Write the formula for the compound dinitrogen tetrafluoride. Write the formula for the compound oxygen difluoride. www.ck12.org Chapter 1. Covalent Formulas and Nomenclature 11. Write the formula for the compound dinitrogen pentoxide. 12. Write the formula for the compound sulfur hexafluoride. 13. Write the formula for the compound tetraphosphorus decaoxide. Answer: 1. carbon monoxide 2. phosphorus trichloride 3. phosphorus pentachloride 4. dinitrogen trioxide 5. boron trichloride 6. sulfur tetrachloride 7. dichlorine monoxide 8. SO3 9. N2 F4 10. OF2 11. N2 O5 12. SF6 13. P4 O10 3