Unformatted text preview: Chapter 5 Chapter 5 Nomenclature 5.1 Naming Compounds
In this section we will discuss a system for naming binary compounds. Binary compounds are those that contain only two types of atoms or ions. For example, NaCl, BaO, Al2O3, and CO2 are binary compounds. Each has only two elements. These compounds are divided into two categories: Compounds containing a metal and nonmetal: CaCl2, BaO, NaCl, etc Compounds containing two nonmetals: SO2, CO2, CO, NO Before we discuss name rules, we should review the information in 4.10 regarding cation charges. Remember that metals will tend to lose electrons. Specifically, the metals in groups 1A 2A and 3A all tend to lose one, two and three electrons respectively. These metals only form one type of cation. In comparison, transition metals can generally form several types of cations. As an example, vanadium (atomic number 23) can form V+, V2+, V3+, V4+ and V5+. Each of these ions is unique and has a specific chemistry. We cannot generally predict which transition metal ion will form my looking at the periodic table. These concepts form the basis for our initial naming method. You should note that there are some exceptions to this rule. For example, lead (Pb) and tin (Sn) are not transition metals but can form several types of ions: Pb2+, Pb4+, Sn2+ and Sn4+. In Addition transition metals zinc (Zn) and silver (Ag) tend to always form Zn2+ and Ag+ respectively. These exceptions should be memorized. 5.2 Naming Binary Inorganic Compounds That Contain a Metal+Nonmetal (Type I and II)
There are two types of binary compounds that form from a metal and a nonmetal: Type I : The cation only forms one type of ion. (Group 1A, 2A, 3A metals) e.g. sodium (Na) is a group IA metal that only forms Na+ Type II : The cation forms more than one type of ion. (Transition metals) e.g. chromium ( Cr), forms Cr3+ and Cr6+ When naming Type I compounds we use the following rules: 1. The cation is always named first and the anion second. 2. A simple cation formed from one element takes its name from the element 3.
name. i.e. Na+ in compounds is called sodium The anion takes its name from element but the suffix –ide is added. i.e. Clbecomes chloride. Consider the following examples: NaCl is named sodium chloride CaCl2 is named calcium chloride AlBr3 is named aluminum bromide When naming Type II we follow the same rules but we must Specify the charge on cation Specify
with roman numerals. with CrCl3 chromium(III)chloride CrCl6 chromium(VI)chloride VBr5 vanadium(V)bromide Remember, the roman number specifies the charge on the cation. When given a chemical formula with a Type II cation, we must determine its charge based on the anion present. Consider CrCl3. We know that this is a Type II compound because it contains a transition metal. The anion in this compound is formed from chlorine. From the figure above, we know that chlorine is a group 7A element. Elements in this group tend to form ions with a charge of -1. CrCl3 contains 3 Cl- ions. To balance the charges so that the net charge is zero, chromium must have a charge of +3. Therefore the name is Chromium(III)chloride. CrCl6 contains 6 Cl- ions. Therefore, the charge on Cr must be +6 to balance the negative charges. By now you should be able to see why roman numerals are necessary. CrCl3 and CrCl6 are two different compounds with a similar name but different chemistry. The roman numeral describes a specific chromium chloride compound Examples: Name the following simple binary compounds: NaI This is a binary compound containing a group 1A metal. Sodium only forms one type of cation (+1). Therefore we do not need to specify charge. The name is sodium Iodide. CaF2 This is a binary compound containing a group 2A metal. Calcium only forms one type of cation (+2). Therefore we do not need to specify charge. The name is calcium fluoride. Al2S3 This is a binary compound containing a group 3A metal. Aluminum only forms one type of cation (+3). Therefore we do not need to specify charge. The name is aluminum sulfide. CaBr2 This is a binary compound containing a group 1A metal. Calcium only forms one type of cation (+2). Therefore we do not need to specify charge. The name is calcium bromide. CoCl2 This is a binary compound containing a transition metal. Therefore we need to specify charge using a roman numeral. The name is cobalt(II) chloride. We determine the charge on cobalt by realizing that Cl is a group 7A element and therefore forms ions of charge -1. CrBr3 This is a binary compound containing a transition metal. Therefore we need to specify charge using a roman numeral. The name is chromium(III) Bromide. We determine the charge on chromium by realizing that bromine (Br) is a group 7A element and therefore forms ions of charge -1. PbO Lead is an exception that forms ions of charge +2 and +4. Therefore, we must specify which ion is present in the compound using roman numerals. The name of this compound is lead(II)oxide. We determine the charge on lead by realizing that oxygen is a group 6A element that forms ions of charge -2. SnO2 Tin is an exception that forms ions of charge +2 and +4. Therefore, we must specify which ion is present in the compound using roman numerals. The name of this compound is tin(IV)oxide. We determine the charge on tin by realizing that oxygen is a group 6A element that forms ions of charge -2. 5.3 Naming Binary Compounds that Contain Only Nonmetals (Type III)
When two nonmetals combine, they are named as if the first element is the cation and the second is an anion. For binary compounds containing nonmetals, prefixes are added so as to indicate the number of atoms present. For example: P2O5 Diphosphorus Pentoxide NO Nitrogen monoxide (note: the mono prefix is not used with the first element) SF6 sulfur hexafluoride Examples: IF5 Iodine pentafluoride AsCl3 Arsenic trichloride SeO Selenium monoxide XeF4 Xenon tetrafluoride NI3 Nitrogen triiodide In general, we can follow this flowchart when naming binary compounds: ...
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