Nomenclature Review

Nomenclature Review Before you can begin naming or writing formulae for chemicals, you need to be able to be able to tell the difference between the different three types of compounds we will be working with: ionic compounds, molecular compounds, and acids. The nomenclature of each of these has some similarities and some differences so you need to know which rules to apply. This review is intended to give you an overview of nomenclature, give you detailed examples of each, and give you practice. Identifying the type of compound being named: Ionic compounds Ionic compounds are made up of positive ions (cations) and negative ions (anions) which are attracted to each other to combine to form neutral “formula units”. This means that one way to identify an ionic compound is to look for cations and ions within the compound. Another way to say this is that all ionic compounds must contain a metal ion or the ammonium ion. Ionic compounds must also be neutral. In order for a compound to be classified as an ionic compound, it MUST satisfy the following criteria: 1) the compound must contain a metal ion or the ammonium ion (NH4+) 2) the compound must be neutral (have an overall charge of 0) Examples of ionic compounds: explanation: Sr(ClO)2 NH4NO3 Sr2+ is a metal ion NH4+ is present Examples of non-ionic compounds: explanation: H2O no metal or NH4+ CrO42not neutral PbS2 NaOH Pb4+ is a metal ion Na+ is a metal ion PO4 no metal or NH4+ C11H22O2 no metal or NH4+ Molecular compounds Molecular compounds are NOT made up from ions at all but instead are formed when two (or more) nonmetal elements share electrons. You can identify a molecular compound by either recognizing that there are no metals, or that all elements in the compound are nonmetals (these mean the exact same thing). Molecular compounds must also be neutral. In order for a compound to be classified as a molecular compound, it MUST satisfy the following criteria: 1) the compound must contain only nonmetal elements (no ions!) 2) the compound must be neutral (have an overall charge of 0) Examples of molecular compounds: CO2 Examples of non-molecular compounds: Fe2O3 explanation: Fe3+ is metal ion C8H10N4O2 N3Cl7 HBr PO43not neutral NH4NO3 NH4+ and NO3- are ions Acids Acids are probably the most easily identifiable type of compound that we are going to deal with, especially when it comes to identifying by name since the word “acid” is in the name of most acids! The part of and acid that actually does the work is hydrogen and by convention the hydrogen is written first when writing the formula of an acid. Also, an acid isn’t an acid unless it is in water which is indicated by putting (aq) after the compounds name (not just acids). In order for a compound to be classified as an acid, it MUST satisfy the following criteria: 1) the compound formula must begin with at least one hydrogen 2) the compound formula must have a subscript (aq) after it 3) the compound must be neutral (have an overall charge of 0) Examples of acids: H3PO4(aq) H2CO3(aq) HC2H3O2(aq) Examples of non-acids: explanation: HI no (aq) NaCl(aq) no H in front NH3(aq) no H in front HF(aq) Writing the name or formula for a compound: Name to formula for MOLECULAR compounds The nomenclature for molecular compounds is similar to ionic compounds in that you start with the first half and then move to the second half. It differs in a major way as well. Molecular compounds are NOT made up of ions so you will not have to worry about charges. What you will have to worry about is how many of each nonmetal make up the molecule you are dealing with. As long as you know the numeric prefixes you should not have much trouble with this. Step 1: Write the symbol and the subscript for the first element Step 2: Write the symbol and the subscript for the second element That’s it. Example: tetranitrogen nonachloride Step 1: N4 Step 2: N4Cl9 (tetra = 4, think tetris!!) (nona = 9, kinda looks like nine) Example: hexaarsenic octaphosphide Step 1: As6 Step 2: As6P8 (hexa = 6, hexagon) (octa = 8, octopus) You try: 1) 2) 3) 4) 5) chlorine pentoxide pentasulfur tetrabromide diphosphorous hexaiodide carbon dioxide dixenon decafluoride Formula to name for MOLECULAR compounds This is pretty much the reverse of above. Step 1: Write the prefix and name for the element (make no changes to the name of the element) Step 2: Write the prefix and name for the second element (change the end of the name of the element to –ide) The prefix “mono” is optional Example: O2F Step 1: dioxygen Step 2: dioxygen monofluoride Example: P3S7 Step 1: triphosphorous Step 2: triphosphorous heptasulfide You try: 1) 2) 3) 4) 5) Br6Cl9 I4Cl5 CO S8O6 HCl Name to formula for ACIDS Acid nomenclature is based solely upon the name of the anion that is paired up with the hydrogen. Because of this it will be impossible for you to name acids without knowing the names of anions. Each of the 3 different anion endings (“ide”, “ite”, and “ate”) have a different relation with the name of the corresponding acid. acid name hydrostemic acid stemous acid stemic acid anion name stemide stemite stemate The easiest way to remember these relationships is that if the acid name starts with hydro, then the anion is monoatomic (like Cl- or S2-). After that, remember the phrase “I ate something icky at the White House” Step 1: Write the symbol for the anion based on the above relationships Step 2: Balance the anion charge by adding hydrogen(s) in front and add (aq) to the end. (the anion charge = # of hydrogens needed) Example: hydrofluoric acid Step 1: The acid name starts with a hydro, so the anion ends with an –ide. That means that it is FStep 2: The acid is HF(aq) Example: carbonic acid Step 1: The acid name end with –ic acid (without a hydro), so the anion ends with an –ate. That means that it is CO3-2 Step 2: The acid is H2CO3(aq) You try: 1) 2) 3) 4) 5) perchloric acid hydrosulfuric acid hypoiodous acid sulfuric acid chlorous acid Formula to name for ACIDS Again, this is pretty much the opposite of the name to formula rules. Step 1: Name the anion based on the above relationships Step 2: Change the ending of the anion name (add the prefix “hydro” if the anion ends with “ide”) and add the word acid Example: HClO4(aq) The anion is ClO4- which is the perchlorate anion, so third relationship applies Ending is changed to –ic, so this is perchloric acid Example: H2SO3(aq) The anion is SO3-2 which is the sulfite anion, so second relationship applies Ending is changed to –ous, so this is sulfurous acid Example: HCN(aq) The anion is CN- which is the cyanide anion, so first relationship applies hydro is put out front and the ending is changed to –ic, so this is hydrocyanic acid Try these: 1) 2) 3) 4) 5) H2CO3(aq) HIO2(aq) HBr(aq) HMnO4(aq) HNO3(aq) Name to formula for IONIC compounds Once you have identified a compound as an ionic compound, you need to be able to write the formula from the name. This is done by following 3 simple (once you have practiced) steps. Step 1: Write the symbol for each ion. Step 2: Find the LCM of the two charges and use it to determine how many cations and how many anions you need in the formula. LCM LCM = # of anions = # of cations charge of cation charge of anion Step 3: Write the formula for the compound: Remember: Parentheses are NOT used for monatomic ions or for single polyatomic ion, only if there are more than one polyatomic ions in the formula. Also remember that you do NOT write the charges in the final formula Example: ammonium carbonate +1 2carbonate = CO3 Step 1: ammonium = NH4 2 2 = 2 cations Æ (NH4)2 = 1 anion Æ CO3 Step 2: LCM of 1 and 2 is 2. 2 1 Step 3: (NH4)2CO3 Note: There are two ammonium ions needed, so the NH4 MUST be in parentheses with the number of cations on the outside of the parentheses. There is only a single carbonate needed, so there must NOT be parentheses. Example: calcium phosphide +2 3phosphide = P Step 1: calcium = Ca 6 6 Step 2: LCM of 2 and 3 is 6. = 3 cations Æ Ca3 = 2 anions Æ P2 2 3 Step 3: Ca3P2 Note: There are no polyatomic ions here, so there will not be any parentheses in the formula. There will NEVER be parentheses unless there is a polyatomic ion present. Example: bismuth (V) arsenate 5+ 3Step 1: bismuth (V) = Bi arsenate = AsO4 15 Step 2: LCM of 5 and 3 is 15. = 3 cations Æ Bi3 5 Step 3: Bi3(AsO4)5 15 Example: titanium (IV) sulfite 4+ 2Step 1: titanium (IV) = Ti sulfite = SO3 4 Step 2: LCM of 4 and 2 is 4. = 1 cation Æ Ti 4 Step 3: Ti(SO3)2 4 3 2 = 5 anions Æ (AsO4)5 = 2 anions Æ (SO3)2 You try: 1) 2) 3) 4) 5) 6) manganese (IV) selenide copper (II) phosphate rubidium oxide calcium perbromate nickel (III) sulfide ammonium hydrogen carbonate Formula to name for IONIC compounds Writing the name of an ionic compound when given the formula is not as bad as it might appear, especially if there is not a VOS present. Wait, VOS? What is that? These are the metals within the red box you saw in class which can take on multiple charges when they form ions. Because they can take on multiple charges, you need to be able to tell which charge they have in a given compound and this is done by putting a roman numeral representing the charge in the name of the ion. For example Cr2+ is called the chromium (II) ion, Cr3+ is called the chromium (III) ion and Cr6+ would be called the chromium (VI) ion. You do NOT need to memorize all of the ions that each VOS metal can take, but you DO need to know which elements are VOS and which aren’t and you need to be able to name them There are only 2 steps for converting an ionic formula to an ionic name: Step 1: Name the cation. Step 1a: If the cation is a VOS metal you need to include the roman numeral for the charge in the cation name. Step 2: Add the name of the anion. It is step 1a that seems to cause the problems, but with a little practice it really isn’t that bad. Because the total positive charge and the total negative charge must be equal to each other (why?) we can figure out the cation charge using the following method: ( # of anions ) • ( charge of anion ) roman numeral = charge of cation = ( # of cations ) This equation itself is not hard to use, the hard part is figuring out what to plug into it. The # of anions and the # of cations come from the subscript values in the formula. Sadly, the only way to identify the charges of the anions is to memorize them. Example: Cr2(SO3)3 Step 1: chromium ( ) (Cr is a VOS so we need to go through step 1a) 2Step 1a: The subscript 3 outside the parentheses tell us that there are 3 SO3 in the compound. The subscript 2 after the Cr tells us that there are 2 Cr in the compound. ( 3 ) • ( -2 ) = 3 Æ chromium (III) (2) Step 2: chromium (III) sulfite Example: AlPO4 Step 1: aluminum Step 2: aluminum phosphate (Al is NOT a VOS so no roman numerals) Example: Mn(CO3)2 Step 1: manganese ( ) (Mn is a VOS so we need to go through step 1a) 2Step 1a: The subscript 2 outside the parentheses tell us that there are 2 CO3 in the compound. The missing subscript after the Mn tells us that there is 1 Mn in the compound. ( 2 ) • ( -2 ) = 4 Æ manganese (IV) (1) Step 2: manganese (IV) carbonate Example: Ca(OH)2 (Ca is NOT a VOS so no roman numerals) Step 1: calcium Step 2: calcium hydroxide Example: K2O (K is NOT a VOS so no roman numerals) Step 1: potassium Step 2: potassium oxide Example: CuClO3 Step 1: copper ( ) (Cu is a VOS so we need to go through step 1a) -1 Step 1a: There is one ClO3 in the compound. You can tell because the ClO3 is not in parentheses. Don’t get confused by the subscript 3 at the end. It is part of the ClO3-1 polyatomic ion and does NOT indicate how many ClO3- ions there are. There is also a single Cu in the compound for the same reason. (1) • ( -1) = 1 Æ copper (I) (1) Step 2: copper (I) chlorate Example: Zn(C2H3O2)2 Step 1: zinc Step 2: zinc acetate (Zn is NOT a VOS so no roman numerals) Example: Sn3(PO3)4 Step 1: tin ( ) (Sn is a VOS so we need to go through step 1a) 3Step 1a: The subscript 4 outside the parentheses tell us that there are 4 PO3 in the compound. The subscript 3 after the Sn tells us that there are 3 Sn in the compound. ( 4 ) • ( -3 ) = 4 Æ tin (IV) (3) Step 2: tin (IV) phosphite Try these: 1) 2) 3) 4) 5) 6) 7) 8) 9) 10) Fe2(CrO4)3 Bi3(AsO4)5 Ag2CO3 Sr(NO2)2 NiPO3 Li2S Al2(SO4)3 CuClO2 Cr(BrO4)3 Be(IO)2 Rules Page Identifying the type of compound being named: Ionic compounds 1) the compound must contain a metal ion or the ammonium ion (NH4+) 2) the compound must be neutral (have an overall charge of 0) Molecular compounds 1) the compound must contain only nonmetal elements (no ions!) 2) the compound must be neutral (have an overall charge of 0) Acids 1) the compound formula must begin with at least one hydrogen 2) the compound formula must have a subscript (aq) after it 3) the compound must be neutral (have an overall charge of 0) Writing the name or formula for a compound: Name to formula for MOLECULAR compounds 1):Write the symbol and the subscript for the first element 2):Write the symbol and the subscript for the second element Formula to name for MOLECULAR compounds 1): Write the prefix and name for the element (make no changes to the name of the element) 2): Write the prefix and name for the second element (change the end of the name of the element to –ide) Name to formula for ACIDS acid name hydrostemic acid stemous acid stemic acid anion name stemide stemite stemate 1): Write the symbol for the anion based on the above relationships 2): Balance the anion charge by adding hydrogen(s) in front and add (aq) to the end. (the anion charge = # of hydrogens needed) Formula to name for ACIDS 1): Name the anion based on the above relationships 2): Change the ending of the anion name (add the prefix “hydro” if the anion ends with “ide”) and add the word acid Name to formula for IONIC compounds 1): Write the symbol for each ion. 2): Find the LCM of the two charges and use it to determine how many cations and how many anions you need in the formula. LCM LCM = # of cations = # of anions charge of cation charge of anion 3): Write the formula for the compound: Formula to name for IONIC compounds 1): Name the cation. 1a): If the cation is a VOS metal you need to include the roman numeral for the charge in the cation name. 2): Add the name of the anion. ( # of anions ) • ( charge of anion ) roman numeral = charge of cation = ( # of cations )