Chapter 5 Naming Inorganic Compounds（1）
Inorganic compound usually are compounds of elements other than carbon, but include carbon oxides, carbonates. Although definitive rules for naming inorganic compounds have been agreed on internationally, many common names for well known compounds are still in use as these rules may lead to rather clumsy names.
Naming Molecular Compounds
For many elements, the most stable form is not the individual atom, but rather a compound. The most common examples of the binary (2-atom) compounds are shown in the following table.
The non-ionic inorganic compounds (molecular inorganic compounds) are similar to these compounds but are combinations of two or more nonmetallic elements through covalent bonds. Most of these compounds combine elements from Groups IVA to VIIA with one another or with hydrogen.
When a hydrogen atom forms compounds with the nonmetals, the hydrogen atom is named first and the nonmetal is named as if it were a negative ion.
• HF (g) hydrogen fluoride... The “g” in the parentheses stands for gas state and must be shown since HF in an aqueous solution is called hydrofluoric acid. This is also done with HCl, HBr and HI, which are all in the same family with HF.
• H2S (g) hydrogen sulfide... In a water solution this would be called hydrosulfuric acid.
The following compounds are exceptions to this rule.
• H2O water... not dihydrogen oxide
• NH3ammonia... not trihydrogen nitride
• CH4methane
When binary compounds are formed from the combinations of other elements,the formula is typically written by placing the elements in order of increasing group number.
The number of atoms is given by a Greek prefix, such as “mono-”, “di-”, “tri-”,“tetra-”, and “penta-”...for 1, 2, 3, 4 and 5...
Always use the whole prefix except for monooxide, which is named monoxide. Never use the mono prefix for the first element and always use a prefix for the second element.
• CO carbon monoxide
• NO nitrogen monoxide
• N2O dinitrogen monoxide... laughing gas
• PC13phosphorus trichloride
• CCl4carbon tetrachloride
Consider the name or formula of the following :
carbon dioxide sulfur trioxide SO2nitrogen dioxide HBr (g) HC1 (g)
Deciding which nomenclature rules to follow:
1. Determine whether the compound is an ionic compound or a molecular one.
If there is a metal, the compound is regarded as an ionic compound. If no metal is present, then the compound is a molecular compound.
If the ammonium ion, NH4+is present, the compound is ionic.
2. If the compound is ionic, use the names and charges listed in the tables below.
3. If the compound is molecular, use the naming rules for binary molecular compounds.
For most of the covalent oxides, name them according to the relative number of atoms of the element and oxygens (e.g., SO2, sulfur dioxide; SO3, sulfur trioxide; N2O3, dinitrogen trioxide). Oxoacids may be thought of as resulting from the hydrolysis of the oxide with the element in the same oxidation state.
• SO2+ H2O = H2SO3sulfur dioxide giving sulfurous acid
• SO3+ H2O = H2SO4sulfur trioxide giving sulfuric acid
• N2O3+ H2O = 2HNO2dinitrogen trioxide giving nitrous acid
Acid anhydride: The product from removing water from an acid, (anhydride, a substance formed by removing the components of water from a compound.) (e.g., the oxides in the above three reactions with water.)
N2O and NO, which are two well-known oxides of nitrogen, have the common names nitrous oxide and nitric oxide, respectively. However they are not the anhydrides of nitrous acid and nitric acid. This emphasizes the point that language of chemistry has developed historically and, as in any language, there are pitfalls for the beginner.
Binary Compounds
In the formula of binary compounds, put the more electropositive element first. The name of the most electronegative element is modified to end in “-ide” and the more electropositive element name is left unchanged.
Taking the binary compound of hydrogen and iodine (HI) as an example, iodine is more electronegative, so it comes last in the name of hydrogen iodide.
• PCl5phosphorus pentachloride • Ca2P3dicalcium triphosphide
• Ni Sn nickel stannide • Cr23C6tricosachromium hexacarbide
Ternary Compounds and Beyond
The following illustrate the principles. There are two ways to name the ternary 2:1:5 compound of antimony, copper, and potassium, depending on which elements are designated as electronegative.
• Cu K5Sb2copper pentapotassium diantimonide... Both copper and potassium are designated as electropositive and they are sequenced alphabetically.
• K5Cu Sb2pentapotassium diantimonide cupride... Only potassium is designated as electropositive and the two electronegative elements, antimony and copper, are sequenced alphabetically.
A 1 : 1 : 1 : 1 quaternary compound can be formed from bromine, chlorine, iodine and phosphorus-
• PBr Cl I phosphorus bromide chloride iodide... With phosphorus being the most electropositive, the other three elements are all designated as electronegative and are sequenced alphabetically.
Naming Ionic Compounds
Ionic compounds are called salts except where the anion is O2-or OH- in which case the compounds are called oxides and hydroxides respectively. Some polyatomic ions have accepted non-systematic names: NH4+, ammonium; H3O+, oxonium (hydronium, also often just called hydrogen ion in aqueous solutions); OH-, hydroxide; CN-, cyanide; N3-, azide.
In nomenclature, polyatomic ions or molecules are often considered to consist of a positively charged species (the charge being indicated by an oxidation number) and neutral or negatively charged species that are surrounding ligands, which each has a pair of electrons on the atom bonded (coordinated) to the central cation. The names for the two common neutral ligands, water and ammonia, are -aqua, H2O, and-ammine, NH3, respectively. Negatively charged ligands have the ending “-o”, (e.g., Cl-, -chloro; OH-, -hydroxo; O2-, -oxo; CN-, -cyano). (The International Union of Pure and Applied Chemistry is considering changing the ending of simple anionic ligands to “-ido”. Therefore, the examples above would then be chlorido, hydroxido, oxido, cyanido.)
Given below is a brief outline of the definitive rules and traditional naming, with examples to clarify the rules.
Systematic naming rules
1. The cation has its name unmodified (i.e., the name of the element).
2. If the anion is monatomic its elemental name is modified to end in “-ide”.
3. If the anion is polyatomic its name is modified to end in “-ate”.
4. When oxidation states need to be indicated, they are shown by Roman numerals in brackets that follow the name of the element.
5. The number of atoms or ligands that are attached to the central atom is denoted by Greek prefixes.
In some ways naming inorganic compounds is quite different from naming organic compounds. This section introduces the common everyday names of well-known inorganic compounds as well as the more formal systematic rules which have been developed.
• KBr potassium bromide • Cu(NH3)4F2tetraamminecopper (II) fluoride
• Na Cl O3sodium trioxochlorate (V) • Fe Cl3iron trichloride or iron (III) chloride
• Ca(OH)2calcium hydroxide • NH4BF4ammonium tetrafluoroborate (III)
The traditional names for Na Cl O3and Fe Cl3are sodium chlorate and ferric chloride, respectively.Note the following points concerning this more traditional method of naming:
1. The endings “-ous” and “-ic” are used for cations of elements existing in only two oxidation states, -ous representing the lower state.
2. The ending “-ite” is used to indicate the oxoanion of oxidation state lower than the common one which ends in “-ate”. An even lower one is “hypo... ite”, and one higher than “-ate” is “per...ate”.
3. The Latin or Greek stem is used for elements with symbols coming from those languages.
• Fe Cl2ferrous chloride • Fe Cl3ferric chloride
• Sn Cl2stannous chloride • Sn Cl4stannic chloride
• KNO2potassium nitrite • KNO3potassium nitrate
• Na2SO3sodium sulfite • Na2SO4sodium sulfate
• NH4Cl O ammonium hypochlorite • NHCl O2ammonium chlorite
• NH4Cl O3ammonium chlorate • NH4Cl O4ammonium perchlorate
Salts can be considered as the product of an acid-base reaction. When an oxide or a hydroxide is the base, water is also a product.
• HNO3+ NH3= NH4NO3(NH4+and NO3-)
• H2SO4+ Ca O = Ca SO4+ H2O (Ca2+and SO42-)
• H3PO4+ 2Na OH = Na2HPO4+ 2H2O (Na+and HPO42-)
The oxoacid corresponding to an “-ate” anion is called the “-ic acid”; to an “-ite” anion is called the “-ous acid”. HCl O is hypochlorous acid; HCl O2is chlorous acid; HC1O3is chloric acid; HC1O4is perchloric acid. (Per is also used in two other ways. One is as shorthand for the peroxo group, -OO-, and the other is for organic compounds where all hydrogen atoms attached to carbon have been replaced by a halogen (e.g., C2F6, perfluoroethane). Thus one must look at the context of the term to determine the meaning.) If the anions in salts of polyprotic acids still have hydrogen atoms attached, the word hydrogen is written before the anion. Therefore, Na H2PO4is sodium dihydrogen phosphate, Na2HPO4is sodium hydrogen phosphate, and Na HCO3 is sodium hydrogen carbonate. In the past the word hydrogen in these salts was often replaced by “bi-” (e.g., Na HCO3, sodium bicarbonate), but it is not approved nomenclature any more.
Anions whose names end in “-ide” have associated acids that have the “hydro-” prefix and an “-ic” suffix:
• Cl-chloride anion • HC1 hydrochloric acid
• S2-sulfide anion • H2S hydrosulfuric acid