Nomenclature Lab

Nomenclature Lab INTRODUCTION Nomenclature Lab INTRODUCTION Whenever you begin study of a new field, what do you have to do first? You have to learn the language of that field. Every field of study has its own vocabulary. Thus, before you can communicate you have to learn the words that people use in that field, or you will have a very hard time learning the concepts that are being taught. This is certainly also true in chemistry. In chemistry we use words that you may or may not have heard before such as electrolysis, effusion, hybridization, resonance, and stoichiometry. Chemists also use words that have a different meaning than the common definition such as the word mole. Therefore, a good grasp of the language of chemistry is critical to your success in a chemistry course. However, studying a new language is difficult and not considered enjoyable by many people. Luckily, when instructors teach chemistry they generally try to use the new words only when they need them making the learning of the language much easier. However, there is one part of the chemical vocabulary that simply can't be put off, and that is the language of chemical nomenclature. When instructors talk about the properties of chemicals (which is what chemistry is!), it is critical that you recognize the chemical that is being discussed. For example, if during the discussion of chemical reactions an instructor mentions that potassium chlorate is heated to produce potassium chloride and oxygen, it is critical that you are able to write the chemical reaction for this process. Thus you must learn chemical nomenclature as soon as possible. As further impetus to your study keep in mind that studies show a good correlation between learning nomenclature and final course grade. That is, students who learn nomenclature early and well have greater success in the course. How do you learn chemical nomenclature? You practice and practice and practice. The following pages contain notes that have been prepared as an aid in your pre-workshop preparation. Please read these over carefully before coming to the laboratory. ASSIGNMENT View the On-line Prelab Presentation of Nomenclature. It is a detailed presentation of the rules of nomenclature. Examples are given in the presentation, as well as, practice problems. Complete the 50 point/50 question on-line quiz. You can find it under “Post-Laboratory” in the on-line program. Unlike the prelab quizzes, you can log out of the quiz at any time without penalty and continue the quiz later. The on-line program times out at 20 minutes. Also, unless you click on the submit button for the particular question you are working on, the program will not count the question against you. For example, if you are working on question 10 when the program times out or you log out, the program will begin at question 10 the next time you log-in to continue the Nomenclature quiz. Nomenclature Lab ASSIGNMENT I. IONIC COMPOUNDS A. Cations 1. Monatomic a) Monatomic cations are most commonly formed from metallic elements. They take the name of the element itself: Na + sodium ion Zn 2+ zinc ion b) If an element can form more than one positive ion, the positive charge of the ion is indicated by following the name of the metal with a Roman numeral in parenthesis: 2+ iron(II) ion Cu + copper(I) ion 3+ iron(III) ion Cu 2+ copper(II) ion Fe Fe Experience is required to know which elements commonly exist in more than one charge state. An older method still widely used for distinguishing between two differently charged ions of a metal uses the endings -ous or -ic; these endings represent the lower and higher charged ions, respectively. They are used together with the root of the Latin name of the element: 2+ Fe 3+ Fe ferrous ion ferric ion Cu + cuprous ion Cu 2+ cupric ion 2. Polyatomic a) The only common polyatomic cations are those given below: + NH4 2+ ammonium ion Hg2 mercury(I) or mercurous ion 2+ The name mercury(I) ion is given to Hg2 because it can be considered to consist + 2+ of two Hg ions. Mercury also occurs as the monatomic Hg ion, which is known as the mercury(II) or mercuric ion. B. Anions 1. Monatomic Negative ions are called anions. Monatomic anions are most commonly formed from atoms of the nonmetallic elements. They are named by dropping the ending of the name of the element and adding the ending -ide: - H hydride ion F - fluoride ion 2- O S 2- oxide ion sulfide ion 3- N P 3- nitride ion phosphide ion Nomenclature Lab ASSIGNMENT 2. Polyatomic a) Only a few common polyatomic ions end in -ide: - OH hydroxide ion CN - 2- cyanide ion O2 peroxide ion b) There are many polyatomic anions containing oxygen. Anions of this kind are referred to as oxyanions. A particular element, such as sulfur, may form more than one oxyanion. When this occurs, rules for indicating the relative numbers of oxygen atoms in the anion are used. When an element has two oxyanions, the name of the one that contains more oxygen ends in -ate; the name of the one with less oxygen ends in -ite: - nitrite ion SO3 - nitrate ion SO4 NO2 NO3 2- sulfite ion 2- sulfate ion When the series of anions of a given element extends to three or four members, as with the oxyanions of the halogens, prefixes are also employed. The prefix hypoindicates less oxygen, whereas the prefix per- indicates more oxygen: ClO - hypochlorite ion (less oxygen than chlorite) ClO2 chlorite ion ClO3 chlorate ion ClO4 perchlorate ion (more oxygen than chlorate) Notice that if these rules are memorized, only the name for one oxyanion in a series is needed to deduce the names of the other members. c) Many polyatomic anions that have high charges readily add one or more hydrogen ions to form anions of lower charge. These ions are named by prefixing the word hydrogen or dihydrogen as appropriate, to the name of the hydrogen-free anion. An older method which is still used, is to use the prefix bi-: - HCO3 hydrogen carbonate (or bicarbonate) ion HSO4 hydrogen sulfate (or bisulfate) ion H2PO4 dihydrogen phosphate ion C. Naming Ionic Compounds The names of cations and anions are combined to name and write the formulas for ionic compounds: sodium chloride NaCl barium bromide BaBr2 Nomenclature Lab ASSIGNMENT copper(II) nitrate Cu(NO3)2 mercurous chloride Hg2Cl2 aluminum oxide Al2O3 The overall zero charge is provided for by adjusting the ratios of cations and anions. In the second example, two Br anions are required to balance the charge of the 2+ single Ba cation. In the third example, two nitrate ions, NO3 , are required to 2+ balance the charge of the Cu ion. Notice that the formula for the entire anion must be enclosed in parentheses so that it is clear that the subscript 2 applies to all the atoms of the anion. The final example, aluminum oxide, is a little more complicated in that more than one of both cation and anion are needed to achieve charge balance. 3+ 2Two Al cations are needed to balance the total charge of three O anions. II. ACIDS This important class of compounds are named in a special way. For purposes of naming, the acids may be thought of as formed from hydrogen ions and an anion. When the anion is a simple monatomic species, the name of the acid has a prefix hydro- and an ending, -ic, as in these examples: - chloride ion (Cl ) hydrochloric acid (HCl) 2- sulfide ion (S ) hydrosulfuric acid (H2S) Many of the most important acids are derived from oxyanions. The name of the acid is related to the name of the anion; when the name of the anion ends in -ate, the name of the acid ends in -ic. Anions whose names end in -ite have associated acids whose names end in -ous. Prefixes in the name of the anion are retained in the name of the acid. These rules are illustrated by the oxyacids of chlorine: - hypochlorite ion (ClO ) chlorite ion chlorate ion (ClO2 perchlorate ion (Continued on next page) ) (ClO3 chlorous acid (HClO2) ) (ClO4 hypochlorous acid (HClO) chloric acid (HClO3) ) perchloric acid (HClO4) Nomenclature Lab ASSIGNMENT III. NON-IONIC COMPOUNDS Before we end this discussion, we will consider the systematic names of compounds that are nonionic. These are named with the more electropositive charged element first. The relative number of atoms of each element is indicated by prefixes; for example, mono-, di-, tri-, tetra-, penta-, and hexa-, which mean 1, 2, 3, 4, 5, and 6, respectively. We use the same suffixes in naming the more negative element as is used in naming ionic compounds. Some examples illustrate the rules: NF3 nitrogen trifluoride CO2 carbon dioxide N2F4 dinitrogen tetrafluoride SO2 sulfur dioxide CO carbon monoxide SO3 sulfur trioxide CCl4 carbon tetrachloride P2O5 diphosphorous pentoxide CHCl3 chloroform NH3 ammonia (trichloromethane) (nitrogen trihydride) The other rules for naming compounds will be used as the need arises. We will also frequently encounter common names of compounds that are still widely used. These compounds were discovered a long time ago and are commonly used in the applied sciences. The common names of these chemicals must simply be memorized.