INORGANIC NOMENCLATURE ~ NAMING INORGANIC COMPOUNDS

Transcription

1 INORGANIC NOMENCLATURE ~ NAMING INORGANIC COMPOUNDS Every compound has its own CHEMICAL FORMULA and its own NAME. The nomenclature (naming systems) for IONIC and MOLECULAR compounds are different. IONIC COMPOUNDS: These consist of any positive ion (except H + ) combined with any negative ion. (If H + is the positive ion, the compound is an acid, as we will see later on page 6.) The positive ion (cation) may be a monatomic metal ion (such as Na + ) or a polyatomic ion (such as NH 4 + ) The negative ion (anion) may be a monatomic non-metal ion (such as Cl - ) or a polyatomic ion (such as SO 4 2- or NO 3 - ) When writing formulas for ionic compounds, the net charge of the formula unit must be zero. (Because the actual formula units are neutral! Oppositely charged ions will come together in a ratio that makes neutral units of the compound. "Neutrality principle") Ex: Ca 2+ and Cl - 2 Cl - and 1 Ca 2+ together have a net charge of zero So the formula is CaCl 2 Case 1. Binary Ionic compounds: Representative (Type I) Metal + Non-Metal Examples: KBr potassium bromide AlCl 3 aluminum chloride Li 3 N lithium nitride Note 1: Metal is always first (name unchanged), non-metal second (the ending of the non-metal is dropped, and the IDE ending is added). Note 2: The name does not indicate how many of each ion are in a formula unit. Exercise: Write formulas for the following cations: barium ion _Ba 2+ _ aluminum ion _ Al 3+ _ potassium ion _ K + _ radium ion _ Ra 2+ Exercise: Write formulas for the following anions: bromide _Br - _ nitride _ N 3- _ iodide _ I - _ oxide _ O 2- _ sulfide _ S 2- _ Exercise: Name the following: NaF sodium fluoride SrI 2 strontium iodide K 2 O potassium oxide Ba 3 N 2 barium nitride MgS magnesium sulfide_ Ca 3 N 2 calcium nitride Al 2 O 3 aluminum oxide Na 3 P sodium phosphide Exercise: Give formulas for the following compounds (refer to periodic table only). cesium phosphide Cs 3 P calcium iodide _CaI 2 _ barium fluoride BaF 2 magnesium nitride Mg 3 N 2 aluminum bromide AlBr 3 sodium selenide _Na 2 Se 1

2 Case 2. Binary Ionic Compounds: Type II Metal + Non-Metal In general, it is NOT possible to use the periodic table to predict what cations (i.e., what the charge on the cation is) are formed by transition metals or the main group metals that are not in Group 1A or 2A. Furthermore, unlike the Group 1A and 2A metals, these other metal elements usually form more than one kind of stable ion. These kinds of metals (and their cations) are called Type II metals (or cations). You will see that you can figure out the charge on a Type II metal cation in a given compound from either its formula or from its name. A few metals not in Group 1A or 2A do form only one kind of stable ion. In this class, the three you need to know are: Al 3+, Zn 2+, and Ag +. Name ionic compounds with these cations as in Case 1. Examples: ZnCl 2 zinc chloride; Ag 2 S silver sulfide; AlF 3 aluminum fluoride. If the metal forms two ions (Type II), the naming systems are as follows: Modern (Stock) system: A Roman numeral after the metal name, in parentheses, indicates the charge on the metal ion. THIS IS THE SYSTEM YOU MUST LEARN IN THIS CLASS! Examples: Fe 3+ is iron(iii) Sn 4+ is tin(iv) Cu + is copper(i) Old system: -ous ending refers to the ion with lower charge. -ic ending refers to the ion with the higher charge. Fe 2+ ferrous Fe 3+ ferric Cr 2+ chromous Cr 3+ chromic Cu + cuprous Cu 2+ cupric Hg +2 2 mercurous Hg 2+ mercuric Sn 2+ stannous Sn 4+ stannic Pb 2+ plumbous Pb 4+ plumbic This information is only included so that if you see these names elsewhere, you'll have some idea why. You do not need to learn these for my class!! Note: The charge on a transition metal ion can be determined from the formula of the compound it is in by using the charge on the anion and applying the "neutrality principle" (for a formula unit). Examples: In FeF 2 there are 2 F - ions per formula unit (net charge of -2) so the charge on the (one) Fe must be +2 (the ion is Fe 2+ ) Name: iron(ii) fluoride (or ferrous fluoride) In Fe 2 O 3 there are 3 O 2- ions per formula unit (total charge = -6) so here the ion is Fe 3+ (two of them must add up to +6). Name: iron(iii) oxide (or ferric oxide) Note: In this class you will ONLY be required to know/give the modern (Stock) name Exercise: Name the following compounds: AgCl silver chloride FeBr 3 iron(iii) bromide Cu 3 N copper(i) nitride Cr 2 S 3 chromium(iii) sulfide Exercise: Give formulas for the following compounds: chromium(iii) oxide _ Cr 2 O 3 _ tin(ii) fluoride SnF 2 iron(iii) iodide _ FeI 3 zinc nitride _ Zn 3 N 2 copper(ii) bromide CuBr 2 _ cobalt(ii) oxide CoO 2

3 Case 3. Ionic Compounds with Polyatomic Ions. Cases 1 and 2 above involve ionic compounds that consist of a metal cation and a non-metal anion two types of elements only. These are called binary compounds. Now let us turn to ionic compounds that are formed from polyatomic ions: (mostly ternary compounds) Note: As before, the charge on a transition metal ion can be determined from the formula of the compound it is in, if the charge on the anion is known. You simply apply the "neutrality principle". You must learn the charges (and names and formulas) of the polyatomic anions! NOTE: you need not memorize C 2 O 4 2- (oxalate), although it appears in this handout. As with all ionic compounds, the cation is named first, then the anion: Examples: (NH 4 ) 2 S ammonium sulfide K 3 PO 4 potassium phosphate Zn(NO 3 ) 2 zinc nitrate Fe 2 (SO 4 ) 3 iron(iii) sulfate (or ferric sulfate) CuCO 3 copper(ii) carbonate (or cupric carbonate) Note: In a formula, parentheses ( ) are used around a polyatomic ion only when there are 2 or more of that polyatomic ion in a formula unit (i.e., when the subscript is not 1). Exercise: Name the following: (NH 4 ) 2 O _ ammonium oxide FeC 2 O 4 iron(ii) oxalate Na 2 SO 3 sodium sulfite (or ferrous oxalate ) CuNO 2 copper(i) nitrite (or cuprous nitrite ) or bisulfate Zn 3 (PO 4 ) 2 _ zinc phosphate Sn(NO 2 ) 2 tin(ii) nitrite Ca(HSO 4 ) 2 calcium hydrogen sulfate (or stannous nitrite ) Exercise: Give formulas for the following: copper(ii) nitrate Cu(NO 3 ) 2 lithium phosphate Li 3 PO 4 silver carbonate Ag 2 CO 3 chromium(ii) hydroxide Cr(OH) 2 barium permanganate Ba(MnO 4 ) 2 mercury(ii) cyanide Hg(CN) 2 nickel(ii) hydroxide Ni(OH) 2 magnesium bicarbonate Mg(HCO 3 ) 2 potassium dichromate K 2 Cr 2 O 7 aluminum hydrogen sulfate Al(HSO 4 ) 3 3

4 MOLECULAR COMPOUNDS When non-metal atoms share electrons with other non-metal atoms, they often form basic units called molecules. Compounds composed of molecules are thus called molecular compounds. We shall learn the nomenclature of (only) binary molecular compounds. Exercise: Define a binary compound A compound made up of only two kinds of atoms (i.e., would separate chemically into exactly two elements) _ Case 4. Binary Molecular Compounds As with binary ionic compounds, the second atom in the formula gets an IDE ending (though it is NOT an ion in these compounds!!! I would not have made this rule!!). Unlike ionic compounds, the number of each atom in each molecule (or formula unit) must be specified with a prefix (because there is no single ratio of combination dictated by the "neutrality principle" [atoms are neutral; there are NO IONS in a molecule!]; there are often many molecular compounds with the same two kinds of atoms [NO 2, NO, N 2 O 4, N 2 O, etc.]). These are the prefixes you need to know: 1 is mono- 2 is di- 3 is tri- 4 is tetra- 5 is penta- 6 is hexa- 7 is hepta- 8 is octa- 9 is nona- 10 is deca- Note: When there is only one atom of the first element, the mono prefix is omitted. Examples: NF 3 nitrogen trifluoride I 2 S diiodine monosulfide P 4 O 10 tetraphosphorus decaoxide B 2 Cl 6 diboron hexachloride Exercise: Name the following: N 2 O 4 dinitrogen tetroxide PCl 5 phophorus pentachloride SO 2 sulfur dioxide SO 3 sulfur trioxide CS 2 carbon disulfide Br 2 O 7 dibromine heptoxide CO carbon monoxide P 2 O 3 diphosphorus trioxide Cl 2 O dichlorine monoxide SF 6 sulfur hexafluoride Exercise: Give formulas for the following: iodine pentabromide IBr 5 chlorine dibromide ClBr 2 oxygen difluoride OF 2 carbon tetrachloride CCl 4 sulfur hexafluoride SF 6 silicon dioxide SiO 2 iodine heptafluoride IF 7 nitrogen monoxide NO dinitrogen trioxide N 2 O 3 Also: You must remember these three very important common names: H 2 O (water) NH 3 (ammonia) CH 4 (methane) 4

5 Case 5. Diatomic Molecular Elements Several common non-metal elements have basic units that are diatomic molecules. The name of the element refers to the diatomic molecular element. For example, hydrogen refers to H 2 and oxygen refers to O 2. (If we mean the atom, we say atomic hydrogen or atomic oxygen). The common diatomic elements are the four halogens, oxygen, nitrogen, and hydrogen. Exercise: List the names and formulas of the 7 elements whose basic units are diatomic molecules: hydrogen (H 2 ), nitrogen (N 2 ), oxygen (O 2 ), fluorine (F 2 ), chlorine (Cl 2 ), bromine (Br 2 ), and iodine (I 2 ) Exercise: Write both the name and formulas (or symbols) of the gases in the following sentence. Dry air contains about 79% nitrogen and 21% oxygen, with small amounts of carbon dioxide, neon, and argon. Polluted air may contain small amounts of sulfur dioxide, sulfur trioxide, nitrogen dioxide, dinitrogen monoxide, chlorine, ammonia, methane, and carbon monoxide. nitrogen (N 2 ), oxygen (O 2 ), carbon dioxide (CO 2 ), neon (Ne), argon (Ar), sulfur dioxide (SO 2 ), sulfur trioxide (SO 3 ), nitrogen dioxide (NO 2 ), dinitrogen monoxide (N 2 O), chlorine (Cl 2 ), ammonia (NH 3 ), methane (CH 4 ), and carbon monoxide (CO) Exercise: Write the name or formula of each compound (or element) in the following paragraph. Probably the most important element found uncombined in nature is O 2. O 2 is quite reactive, forming compounds with the halogens F 2, Cl 2, Br 2 and I 2. O 2 forms two compounds with H 2. Following the usual rules of nomenclature, the most common oxide of hydrogen, whose formula is H 2 O, would be named dihydrogen monoxide. The other oxide of hydrogen is H 2 O 2. O 2 forms a series of compounds with N 2, many of which are atmospheric pollutants, including NO, N 2 O, NO 2, N 2 O 4, N 2 O 5. O 2 (oxygen), F 2 (fluorine), Cl 2 (chlorine), Br 2 (bromine), I 2 (iodine), H 2 (hydrogen), H 2 O (dihydrogen monoxide), H 2 O 2 (dihydrogen dioxide, by following the rules you know, although that isn't actually the formal name don't worry about it for now), N 2 (nitrogen), NO (nitrogen monoxide), N 2 O (dinitrogen monoxide), NO 2 (nitrogen dioxide), N 2 O 4 (dinitrogen tetroxide), N 2 O 5 (dinitrogen pentoxide) 5

6 Case 6. ACIDS As a group, ACIDS are a somewhat unusual subcategory of molecular compounds. They have the (seemingly strange) property that when dissolved in water, at least some of the formula units separate into a hydrogen ion, H +, and an anion. So even though they are molecular compounds, we can think of them as being like an ionic compound formed from H + and an anion. Since they form at least some ions in aqueous solution, they are called "electrolytes" (soluble ionic compounds are also called "electrolytes" for the same reason). The naming system for acids is different from that of either ionic or molecular compounds. The key to naming all acids is knowing the name of the anion from which it is derived. If the anion does NOT contain oxygen: Add the prefix hydro and suffix "-ic" to the root of the anion name (and add the word "acid"). Ex: HCl. Anion is chloride, root is chlor. Name of acid is hydrochloric acid. HCN. Anion is cyanide, root is cyan. Name of acid is hydrocyanic acid If the anion DOES contain oxygen: Look at the ending of the anion name: If the ending is -"ate", add the suffix "-ic" to the root of the anion (and add the word "acid") Ex: HNO 3. Anion is nitrate, root is nitr. Name of acid is nitric acid. If the ending is -"ite", add the suffix "-ous" to the root of the anion (and add the word "acid") Ex: HNO 2. Anion is nitrite, root is nitr. Name of acid is nitrous acid. Some acids, called strong acids, have the property that ALL of their formula units separate into ions in aqueous solution. These acids are often used in industry and in the laboratory. You must learn the names and formulas of the six common strong acids: HCl hydrochloric acid HBr hydrobromic acid H 2 SO 4 sulfuric acid HI hydroiodic acid HNO 3 nitric acid HClO 4 perchloric acid Other acids, called weak acids, have the property that only a few percent or less of their dissolved formula units separate into ions most of the formula units remain as intact molecules in aqueous solution. You need not memorize which acids are weak acids! Why not? You can use deductive reasoning here! If an acid is not one of the six strong ones that you memorized above, then it must be weak!! Several common weak acids are: HC 2 H 3 O 2 acetic acid H 3 PO 4 phosphoric acid H 2 CO 3 carbonic acid H 2 C 2 O 4 oxalic acid Exercise: Write the formulas for the underlined acids in the following paragraph: In industry, hydrochloric acid is known as muriatic acid and is used in concrete work. Since sulfuric acid is used in automobile batteries, it is commonly called battery acid. Nitric acid is probably the most common oxidizing agent used in laboratories. Acetic acid is the acid in vinegar. Phosphoric acid and carbonic acid are added to soft drinks to provide a pleasantly tart taste. Oxalic acid is found in many plants, including rhubarb and spinach. A high concentration of this acid is toxic. HCl (hydrochloric acid); H 2 SO 4 (sulfuric acid); HNO 3 (nitric acid); HC 2 H 3 O 2 (acetic acid); H 3 PO 4 (phosphoric acid); H 2 CO 3 (carbonic acid); H 2 C 2 O 4 (oxalic acid) 6

7 Exercises for Further Practice Name the following (HINT: You must first decide whether or not the substance is an ionic compound, a molecular compound (that is not an acid), an acid, or a molecular element): Na 2 SO 4 P 2 O 5 Br 2 BaCO 3 Fe(NO 3 ) 2 PbO 2 SiCl 4 AgClO (NH 4 ) 2 C 2 O 4 HNO 3 CuCrO 4 PbCr 2 O 7 SeI 2 sodium sulfate diphosphorus pentoxide bromine barium carbonate iron(ii) nitrate lead(iv) oxide silicon tetrachloride silver hypochlorite ammonium oxalate nitric acid copper(ii) chromate lead(ii) dichromate selenium diiodide CuHPO 4 copper(ii) hydrogen phosphate (or copper(ii) biphosphate)_ SF 4 HgCl 2 Br 2 O KClO Sn(ClO 3 ) 2 NaH 2 PO 4 sulfur tetrafluoride mercury(ii) chloride dibromine monoxide potassium hypochlorite tin(ii) chlorate sodium dihydrogen phosphate 7

8 Give Formulas for the Following: zinc phosphate Zn 3 (PO 4 ) 2 tin(ii) hydroxide Sn(OH) 2 ammonium nitrite NH 4 NO 2 copper(ii) acetate Cu(C 2 H 3 O 2 ) 2 lithium sulfite Li 2 SO 3 silver dichromate Ag 2 Cr 2 O 7 sulfur trioxide SO 3 sulfuric acid H 2 SO 4 nickel(ii) chlorate Ni(ClO 3 ) 2 chromium(iii) bromide CrBr 3 iron(iii) chromate Fe 2 (CrO 4 ) 3 bromine Br 2 strontium nitrate Sr(NO 3 ) 2 iron(ii) hydroxide Fe(OH) 2 calcium carbonate CaCO 3 ammonium sulfite (NH 4 ) 2 SO 3 copper(ii) phosphide Cu 3 P 2 lead(iv) sulfide PbS 2 lead(iv) acetate Pb(C 2 H 3 O 2 ) 4 potassium dichromate K 2 Cr 2 O 7 titanium(iv) chloride TiCl 4 chromium(ii) oxide CrO diboron hexafluoride B 2 F 6 cobalt(ii) bromide CoBr 2 aluminum dihydrogen phosphate _Al(H 2 PO 4 ) 3 magnesium carbonate MgCO 3 strontium sulfite SrSO 3 oxygen difluoride OF 2 phosphoric acid H 3 PO 4 nitrogen N 2 calcium hydroxide Ca(OH) 2 ammonium oxalate (NH 4 ) 2 C 2 O 4 sodium hypochlorite NaClO (or NaOCl) magnesium nitrate Mg(NO 3 ) 2 iron(iii) cyanide Fe(CN) 3 silver phosphate Ag 3 PO 4 potassium permanganate KMnO 4 iron(ii) hydrogen sulfate Fe(HSO 4 ) 2 zinc sulfide ZnS carbonic acid H 2 CO 3 lead(ii) hydrogen carbonate Pb(HCO 3 ) 2 gold(iii) bromide AuBr 3 8