Chapter 6 Chemical Nomenclature Section 6.1 Introduction to Nomenclature Nomenclature: A system of names used in a science. The key to learning such a system is to minimize memorization and develop an understanding of a systematic procedure for naming chemical compounds. Section 6.2 Formulas of Elements Goal 1 In Chapter 5 you learned the symbols of 35 elements. In this chapter you will learn the chemical formulas of those elements. Given a name or formula of an element in Figure 5.9, write the other. 1
Molecule: The tiniest independent particle of a pure substance. For most elements, the smallest independent particle is a single atom. Their formula is the elemental symbol. Element Helium Lithium Examples Formula He Li Seven elements form diatomic molecules under normal conditions Di- means two The smallest particle of these elements is two atoms that are chemically attached to each other The chemical formula of a diatomic molecule is the elemental symbol followed by a subscript of 2 7 elements occur in nature as diatomic (two-atom) molecules: the formula of hydrogen is H 2 the formula of nitrogen is N 2 the formula of oxygen is O 2 the formula of fluorine is F 2 the formula of chlorine is Cl 2 the formula of bromine is Br 2 the formula of iodine is I 2 Some other elements commonly form polyatomic (many-atom) molecules. However, their natural molecular form varies, so we will write their formulas as if they were monatomic (one-atom) species. This will not affect calculations involving these elements. He Element carbon phosphorus sulfur Formula C P S 2
Cl 2 S or S 8 P or P 4 Section 6.3 C or C 60 Compounds Made from Two Nonmetals Goal 2 Goal 3 Given the name or formula of a binary molecular compound, write the other. Given the name or the formula of water, write the other; given the name or the formula of ammonia, write the other. 3
The stair-step line in the periodic table separates elements on the left that are metals from elements on the right that are nonmetals. Several elements bordering on this line are metalloids or semimetals. Compounds formed by two nonmetals or a metalloid and a nonmetal are called binary molecular compounds. Naming binary molecular compounds: 1. The first word is the name of the first element in the compound, modified with a prefix to indicate the number of atoms of that element in the molecule. 2. The second word is the name of the second element in the compound, changed to end in -ide, modified with a prefix to indicate the number of atoms of that element in the molecule. 1 2 3 4 5 6 7 8 9 10 monoditritetrapentahexaheptaoctanonadeca- Examples: Write the name of I 2 O 5. 2 = di- I = iodine first word is diiodine 5 = penta- O = oxygen change 2nd word to end in -ide = oxide second word is pentoxide Answer: diiodine pentoxide Write the formula of nitrogen trifluoride. No prefix on first word = mono- is implied: 1 The symbol of nitrogen is N 2nd word prefix tri- = 3 -fluoride is an -ide modified fluorine = F Answer: NF 3 Two important exceptions to the binary molecular compound nomenclature rules: H 2 O is water NH 3 is ammonia 4
Section 6.4 Names and Formulas of Ions Formed by One Element Goal 4 Given the name or formula of an ion in Figure 6.3, write the other. Ion: Charged particle formed when a neutral atom or molecule loses or gains electrons Cation: Positively-charged ion. Formed when a neutral atom or molecule loses one or more electrons. Figure 6.3 Anion: Negatively-charged ion. Formed when a neutral atom or molecule gains one or more electrons. Monatomic ion: Ion formed from a single (mono-) atom Name of a monatomic cation: Name of element, followed by the word ion Formula of a monatomic ion: Elemental symbol followed by superscript size of charge and sign of charge (if the size of the charge is 1, the 1 is omitted) Name of a monatomic anion: Name of element changed to end in -ide, followed by the word ion 5
The charge on a main-group (U.S. A group) ion corresponds to its group number: Examples: What is the the formula of sodium ion? Group 1A 2A 3A 5A 6A 7A Charge 1+ 2+ 3+ 3 2 1 Sodium is in Group 1A, so its ion has a 1+ charge We write the symbol of the element, followed by the charge in superscript, omitting the 1 Na + What is are the name and formula of the ion formed from a sulfur atom? Sulfur is in Group 6A, so it forms 2 ions; write the symbol of the element, followed by the charge in superscript: S 2 A monatomic anion is named by changing the name of the element to end in -ide, followed by the word ion: sulfide ion Many transition elements (U.S. B groups) form multiple ions with different charges All transition-element ions have a positive charge To distinguish among the ions, the magnitude of the charge is included with its name: Cr 2+ is chromium(ii) ion Cr 3+ is chromium(iii) ion Three of the transition element ions almost always occur with only one charge, so chemists do not write the magnitude of the charge in their names: Ni 2+ is nickel ion Zn 2+ is zinc ion Ag + is silver ion The mercury(i) ion is a special case: it is a diatomic (two-atom) ion: Hg 2 2+ It is named as if single atoms existed separately: mercury(i) ion You must memorize their charges 6
Example: What is the formula of copper(ii) ion? What is the name of Zn 2+? The symbol for copper is Cu (II) indicates the 2+ ion Cu 2+ The name of Zn is zinc Zinc has just one common charge, so its charge is not included in its name zinc ion Section 6.8 Formulas of Ionic Compounds Ionic compound: A combination of cations and anions that form a crystalline solid Must be electrically neutral How to Write the Formula of an Ionic Compound Write the formula of the cation, followed by the formula of the anion, omitting the charges Insert subscripts to show the number of each ion needed in the formula unit to make the sum of the charges equal to zero with the fewest number of ions possible If only one ion is needed, omit the subscript If a polyatomic ion is needed more than once, enclose the formula of the ion in parentheses and place the subscript after the closing parenthesis Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Second Third Edition Copyright 2007 2004 Examples: What is the formula of magnesium chloride? Refer to this table for your Polyatomic ions. Some General Chemistry Courses will require you to memorize most of these. Be prepared to do that!!! Magnesium ion is in Group 2A/2, so its formula is Mg 2+ Chlorine is in Group 7A/17, so chloride ion is Cl Two 1 ions are needed to balance the 2+ ion MgCl 2 7
What is the formula of aluminum oxide? Aluminum is in Group 3A/13, so aluminum ion is Al 3+ Oxygen in in Group 6A/16, so oxide ion is O 2 The least common multiple of 2 and 3 is 6, so 2 x 3+ balances 3 x 2 Al 2 O 3 What is the formula of barium nitrate? Barium is in Group 2A/2, so barium ion is Mg 2+ The formula of nitric acid is HNO 3, so nitrate ion is what results when the H + is removed, so it is a 1 ion, NO 3 Two 1 ions are needed to balance the charge of the 2+ ion, and to retain the identity of the nitrate ion, enclose it in parentheses Ba(NO 3 ) 2 Goal 9 Section 6.9 Names of Ionic Compounds Given the formula of an ionic compound made up of identifiable ions, write the name of the compound. How to Write the Name of an Ionic Compound Examples: Write the name of the following compound: Write the name of the cation Write the name of the anion To name an ionic compound containing a metal that commonly is capable of having more than one ionic charge, the compound name includes the charge of that metal Zn(NO 3 ) 2 Zinc ion has only one common charge, 2+, so the magnitude of the charge is not included in its name: zinc ion NO 3 comes from the memorized acid HNO 3, nitric acid -ic changes to -ate: nitrate ion zinc nitrate 8
Examples: Write the name of the following compound: CoCl 2 Cobalt ion has more than one common charge Chlorine, Cl, is in Group 7A/17, so it forms a 1 ion that ends in -ide: chloride ion Two 1 ions means the positive charge must be 2+: cobalt(ii) ion cobalt(ii) chloride Section 6.11 Summary of the Nomenclature System Section 6.12 Common Names of Chemicals 9
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