Nomenclature. Why, Learn it? History:

Transcription

1 Nomenclature Why, Learn it? Allow us to be able to name compound we have never seen before. If we know the name of a compound we can determine its formula. We can look at a formula, determine it name and be able to look it up. History: Common names were Okay when there was only a few compounds known, but as the number of compounds grew, it was hard to keep track of the names. There was a need for a system of naming, but people don t like change. 1

2 Common names: Pros: they were familiar they often told about an important property associated with the compound they often gave glory to the chemist who discover or synthesis the compound Cons: they had to be memorized they told you nothing of the formula if two chemist discover the same compound, they wouldn t know the number of compounds was growing rapidly The first order system: The first system of nomenclature was based of different ending meaning different charged states. Many element were named after their Latin names (i.e. Iron as ferric or ferrous). This system paved the way for the current system of naming. IUPAC International Union of Pure and Applied Chemistry 2

3 Two main types of compounds: Molecular Usually involves two nonmetal. Easier to name. Easier to convert to a formula. We will not be naming organic molecule, at this point. Ionic Usually a metal and a nonmetal. Has a cation (+) and an anion (-) Has two basic groups You do not need to memorize all the polyatomic ions Includes acids, even though they are not really truly ionic We need to learn two main things for each group: How to look at a chemical formula and determine the name of the compound How to look at a name and determine the correct chemical formula for the compound Naming Binary Molecules: The first element in the compound it is name directly after it element name if there is more than one atom of the element present in the molecule, then a prefix must be added to the name The second element in the compound it is name after it element but the ending of the name is removed and an -ide is added (based on how it sounds) a prefix should always be used to show how many atoms of that element are present in the molecule (even if there is only one) 3

4 The Prefixes Mono- is one Octa- is eight Di- is two Nona- is nine Tri- is three Deca- is ten Tetra- is four Penta- is five Hexa- is six Hepta- is seven NOTE: after the tetra the prefix are the same as those associated with geometric designs Examples SO 2 S is sulfur O is oxygen and become oxide there is only one S therefore no prefix there are two O so you use the prefix di- sulfur dioxide N 2 O 4 N is nitrogen O is oxygen and become oxide there is two N therefore use di- there are four O therefore use tetra- dinitrogen tetraoxide From the Name to the Formula: Put the element symbol down The prefixes tell subscript 4

5 Examples disulfur decafluoride sulfur is S there are two S fluoride is F there are ten F S 2 F 10 nitrogen trifluoride nitrogen is N there is one N fluoride is F there are three F NF 3 Naming Binary Ionic Compound The first element is the cation (usually a metal) The second element is the anion (usually a nonmetal) The metal is named after it element The nonmetal is named after it element but the ending is removed and replaced with - ide More Rules to Naming If the Metal has more than one charge state possible then it charge is designated by a Roman Numeral in ( ) Copper can be +1 or +2 so it could be copper(i) or copper (II) Iron can be +2 or +3 so it could be iron(ii) or iron(iii) You must determine the charged state based on the other element in the compound 5

6 Examples NaF Na is sodium the Na is +1 and can only be +1 F is fluorine and becomes fluoride the F is a -1 Fe 2 O 3 Fe is Iron the Fe is +3 Fe can exist in more than as two charges therefore iron(iii) is needed O is oxygen and becomes oxide the O is a -2 From Name to Formula Determine what the symbol is for each element involved Write down the symbols If you are told a charge (roman numeral) write it above the element Write down the charge of any other ions you know Balance the compound for charge using subscripts (i.e. you want the total charge to be zero) Examples Copper (I) Oxide Copper is Cu Barium Chloride Barium is Ba Oxide is O CuO is the symbols Cu is +1 O is -2 therefore you need two Cu per O Chloride is Cl BaCl is the symbol Ba is +2 Cl is -1 therefore you need 1 Ba for 2 Cl Cu 2 O BaCl 2 6

7 Ionic Involving Polyatomic Ions The rules are similar to ionic binary compounds If there is a polyatomic ion in the formula: just use its name as it appears in the chart There are only two polyatomic cation you need to know ammonium and hydronium To take a name to the formula treat a polyatomic just like a normal ion and balance for charge Examples of naming with polyatomics: KMnO 4 K is potassium K only has one charge state MnO 4 is permanganate Put them together potassium permanganate Sb(ClO 3 ) 3 Sb is Antimony Sb not sure if it has more than one charge state ClO 3 is Clorate and has a -1 charge calculate Sb has a charge of +3 look up to see if only one charge or use roman numeral antimony (III) chlorate Examples of formula from name for polyatomics: Chromium(III) sulfate Chromium is Cr and has a +3 charge Sulfate is SO 4 and has a -2 charge need 2 Cr for 3 SO 4 to balance charge Cr 2 (SO 4 ) 3 ( ) are needed to show ion unit Barium arsenate Barium is Ba and is found in the 2nd row so it has a +2 charge Arsenate is AsO 4 and has a -3 charge need 3 Ba for 2 AsO 4 to balance charge Ba 3 (AsO 4 ) 2 ( ) are needed 7

8 Acid are hard, Here the rules: You need to be able to recognize acids Usually H start the formula Oxy-acid contain Oxygen (usually in a polyatomic ion) In order for an acid to be named as an acid it should be aqueous Binary acid are hydrogen and a nonmetallic element More acid rules: Hydro state the hydrogen is present The nonmetal element is named as a anion with the -ide removed and replaced with a -ic Finally the word acid is added at the end of the name To take the name to the formula put down H and the anion indicated and balance for charge Don t forget the (aq) to show it is in water Still more acid rules: If the acid has a polyatomic ion you need to remember if the polyatomic ion ends in -ate then remove it and add -ic if the polyatomic ends in -ite then remove it and add - ous Don t use the hydro just start with the polyatomic When dealing with polyatomic based acids there are many exceptions 8

9 Example of Acids HBr H means it an acid, use hydro- Br is bromine it become bromic add acid at the end hydrobromic acid HNO 2 H means it an acid NO 2 is polyatomic, no hydro is needed NO 2 is a nitrite, the ite is removed and replaced with -ous add acid at the end nitrous acid Example of acid: Hydrochloric acid Acid tells us to use a H at the first, we use H as +1 Chloric tells us there is a Cl, we know Cl is -1 H charge and Cl charge are balanced HCl (aq) need (aq) to show that it is in water Sulfuric acid Acid tells us use H first, we use H as +1 Sulfuric end in -ic so the polyatomic must end in -ate Sulfate is SO 4 and has a -2 charge need 2 H to balance 1 SO 4 ion H 2 SO 4(aq) need (aq) The end 9