Nomenclature – The Naming of Compounds

Nomenclature – the naming of compounds A. Ionic compounds (metal with a nonmetal) Consider the compound to be made-up of two parts: a positive charged atom and a negatively charged atom. 1) When naming such a chemical species the more metallic (or positively charged atom) is stated first followed by the nonmetal (or negatively charged atom). The nonmetal element name is altered by usually dropping the last part of the element's name and adding the suffix "IDE." Example: CsI - cesium iodide AlCl3- aluminum chloride BaBr2 - Barium bromide 2) When the more positive ion is a transition metal, the oxidation state of the element is designated using Roman Numeral. Example: NiCl - nickel (I) chloride Cu(NO3)2 - copper (II) nitrate 3) Some transition metals have a "Latin Roots associated with them. If this is the case, the metal can also be named using its Latin Root prefix. The suffixes "IC" and "OUS" are used to represent the higher and lower oxidation state of the ion, respectively. Example: FeO - ferrous oxide Fe2O3 - ferric oxide FeO - iron (II) oxide Fe2O3 - iron (III) oxide B. Covalent/Molecular compounds (two nonmetals) 1) The first element (or the more metallic of the nonmetallic element) is stated first, again followed by the second element, least metallic of the elements in the compound. The nonmetal element name is altered by usually dropping the last part of the element's name and adding the suffix "IDE." Prefixes are used to distinguish the number of atoms of each atom in the molecule. Prefixes: mono, di, tri, tetra, penta, hexa, hepta, octa, nona and deca Examples: PCl5: phosphorous pentachloride CO: carbon monoxide P4O10: tetraphosphorous decaoxide 2) Some compounds are always referred to by their common name: Examples: NH3 – ammonia H2O – water C. Polyatomic Ions Polyatomic ions are charged clusters of atoms. Ions are considered to be polyatomic if two or more different non-metal elements come together to form an ion. Polyatomic ions can be positively or negatively charged. Examples: Cr2O7-2 - dichromate ion NH4+ - ammonium ion D. Oxyanions Oxyanions are polyatomic ions that have one or more oxygen atoms present in the ion. Examples of elements, which tend to form oxyanions are the nonmetals (except for the fluorine atom), and many of the metalloids. Example: CO3-2 - carbonate ion IO3- - iodate ion PO4-3 - phosphate ion ClO3- - chlorite ion AsO3-3 - arsenite ion When an element forms only two oxyanions they are named as follows: The ion having the greater number of oxygen atoms present ends in the suffix "ATE". Whereas the ion having the fewer number of oxygen atoms is given the "ITE" ending. Example: NO3- - nitrate ion NO2- - nitrite ion If the element forms a series of oxygen containing ions the following naming system is employed: ClO- - hypochlorite ion ClO2- - chlorite ion ClO3- - chlorate ion ClO4- - perchlorate ion E. Acids Acids are compounds that produce or donate a hydrogen ion(s) (proton) to another substance in solution. An acid can be classified as being either a strong or weak acid. This designation does not indicate their ability to cause burns, but describes their ability to dissociate (ionize) in a solvent, such as water. Strong acids are compounds, which TOTALLY dissociate when dissolved in water. Whereas a weak acid is a chemical substance which only PARTIALLY dissociates when dissolved in water. Examples of Common Acids: Strong Acids: HCl - hydrochloric acid HI - hydroiodoic acid HBr - hydrobromic acid HNO3 - nitric acid HClO4 - perchloric acid H2SO4 - sulfuric acid Weak Acids (most acids are considered to be weak): HF - hydrofluoric acid CH3 COOH - acetic acid H3PO4 - phosphoric acid H2SO3 - sulfurous acid H2CO3 - carbonic acid The naming of acids may seem arbitrary at first, but there is a system. Compounds having the "IDE" ending that can form an acid in water, replace their "IDE" suffix and take on the "IC" ending. Example: HCl (g) hydrogen chloride gas dissolved in water yields HCl (aq), hydrochloric acid Polyatomic ions, which combined with hydrogen ions to form an acid, exchange their "ATE" ending for "IC" suffix and their "ITE" suffix for "OUS". Example: SO4-2 (sulfate ion) when combined with two hydrogen ions will form the acid H2SO4, sulfuric acid. SO3-2 (sulfite ion) when combined with two hydrogen ions will form the acid H2SO3, sulfurous acid. F. Bases Bases are chemical substances, which accept a proton from another compound when in solution. As it was with the acids, bases can be classified as being either strong or weak with regard to their ability to ionize/dissociate in water. Strong bases are usually formed when the hydroxide ion (OH-) combines with the alkali and alkaline earth metals. A common group of compounds, which are considered to be weak bases, is ammonium and its derivatives. Example of Common Bases: Strong Bases: Ca(OH)2 - calcium hydroxide NaOH - sodium hydroxide Weak Bases: NH3 - ammonia NaHCO3 (aq) - sodium bicarbonate or sodium hydrogen carbonate Unlike the acids, bases do not exchange prefixes for special designation