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Chemical Formulas and Nomenclature CHAPTER 7 In the next few slides we will be looking at how to write formulas and names for three different types of chemical compounds: • 1. IONIC COMPOUNDS • 2. MOLECULAR COMPOUNDS • 3. ACIDS *Each type will have a set of rules that we must follow to correctly represent the substance. What can you tell us about bonds between atoms? Notes Sheet 4 ionic PC NPC metallic electrons are transferred polar covalent (unequal share) nonpolar covalent (equal share) electrons are “delocalized” *electronegativity measures “electron pull” in a bond 2.3 1.9 0.5 ionic PC PC 1.3 1.3 2.2 PC PC ionic 0 0.4 0.2 NPC PC NPC How do we begin to write ionic FORMULAS? Because atoms want to reach an octet of outer electrons, the positive or negative charges (oxidation numbers) can be predicted for single (monatomic) atoms. But HOW do we predict the charges (oxidation numbers) of monatomic ions? 0 1+ Because an1Ohhh, metalswant tendto toreach have 2+ atoms 3+ 3- 2octet numbers. positive oxidation of outer electrons, the positive (lose e-) variescharges +1 totend +7 (oxidation or negative Nonmetals to have numbers) can be predicted for negative oxidations single (monatomic) numbers. (gain atoms. e-) varies We use these charges to create “neutral” compounds… Why is aluminum oxide Al2O3? Criss Cross Method of Writing Formulas • This method crosses charges and subscripts to form neutral compounds. Al +3 and O-2 Al and O Al2O3 (neutral) How do we write oxidation numbers for transition elements? The charges on transition metal ions must be indicated. One method is shown here: The Roman numeral (stock system) gives the charge (oxidation number) of the cation: Ex: Nickel (II) is Ni+2 Nickel (III) is Ni+3 Hey, What are Polyatomic Ions? Criss-Cross Method of Writing Formulas…. Notice a trend between the oxidation/charges of ions and the subscripts of elements. Ex: Al+3 and SO4-2 gives Al2(SO4)3 Naming Overview… metal + nonmetal (cation followed by anion) cation = element name anion = element root-ide Metal/polyatomic ion + NM/polyatomic ion cation followed by anion cation = element or polyatomic ion name anion = element or polyatomic ion name cation = element (charge) using roman numerals anion = same as above Naming Ionic Compounds Ex: Al2O3 Aluminum and Oxygen Aluminum oxide cation anion Naming ionic compounds RECALL: metal + nonmetal cation followed by anion cation = element name anion = element root-ide Na+ Cl- sodium chloride Li+ H- lithium hydride Ca2+ S-2 Al3+ Claluminum chloride calcium sulfide Mg2+ O-2 magnesium oxide Na+ N-3 sodium nitride Naming Ionic Compounds with Polyatomic Ions RECALL: cation = element name OR polyatomic name anion = element root-ide OR polyatomic name Na+ SO42sodium sulfate iron(II) nitrate sodium perchlorate K+ H2PO4potassium dihydrogen phosphate Naming Ionic Compounds with Transition Metals RECALL: cation = element (charge) anion = element root-ide Cu+ Clcopper(I) chloride Hg2+ O2mercury(II) oxide Fe3+ O2- Pb2+ Cl1iron(III) oxide lead(II) chloride Co2+ Br1Mn4+ O2manganese(IV) oxide cobalt(II) bromide Formula? Notes sheet 5 Practice Naming Ionic Compounds EX: AgCl is __________________ Silver chloride Na2O is ___________________ Sodium oxide CaBr2 is ___________________ Calcium bromide PbO2 is ___________________ Lead (IV) oxide Practice Naming Ionic Compounds Ex: Li2CO3 is ____________________ Lithium carbonate Ba(OH)2 is ___________________ Barium hydroxide Zn(NO3)2 is __________________ Zinc nitrate KClO3 is ___________________ Potassium chlorate Naming continued… Name the following compound: Ba(Na)2 BaNaNa! How do we write oxidation numbers for transition elements? The oxidation number of a transition element can be determined by TWO methods. 1. The Roman numeral (stock system) indicating the charge (oxidation number). Ex: iron (II) is Fe+2 iron (III) is Fe+3 2. The suffix ending (old system): Ex: ferrous is Fe+2 ferric is Fe+3 Notes Sheet 5 Lower ion charge = root -ous ending chromous oxide chromium (III) oxide cobaltous chloride cobalt (III) chloride lead (II) chloride mercury (I) chloride plumbic chloride mercuric oxide Higher ion charge = root -ic ending Naming Binary Molecular Compounds • Unlike ionic compounds, molecular compounds are composed of individual covalently bonded units, or molecules. • Covalent compounds are formed between nonmetals. • Prefixes are used to indicate number of each type of element in the compound. • Write the prefixes as indicated on the next slide…. Molecular Prefixes 1 mono- 6 hexa- 2 di- 7 hepta- 3 tri- 8 octa- 4 tetra- 9 nona- 5 penta- 10 deca- (decade) Naming covalent compounds monotri- pentahexa- octa- deca- -use prefixes for each element -“mono” left off for FIRST element -double vowels usually drop (a) phosphorous pentachloride sulfur hexafluoride sulfur dioxide sulfur trioxide carbon dioxide tetraphosphorous decoxide dinitrogen pentoxide dichlorine heptoxide hydrogen peroxide methane nitrous oxide, laughing gas N2H4 CCl4 P2O3 Cl2O7 CO2 CS2 IF NI3 H2O PH3 NH3 RECALL: All non-metals! Named similarly to binary ionics… …but now prefixes are used. “mono-” is never used for 1st element dinitrogen monoxide phosphorus trichloride sulfur hexafluoride dinitrogen pentoxide suflur dioxide hydrogen peroxide Practice Naming Binary Molecular Compounds Ex: SO3 is ____________________ sulfur trioxide PBr5 is ____________________ phosphorus pentabromide ICl3 is _____________________ iodine trichloride H2O is _____________________ dihydrogen monoxide Sb2O3 is _____________________ diantimony trioxide (*metalloid) Strange Names for Molecules BUCKMINSTER FULLERENE MORONIC ACID ARABITOL CRAPINON MEGAPHONE BUTANAL Add to NOTES PACKET CONTENT! Looks like “H + anion” Name is based on anion suffix. “-ate” → “-ic acid” “-ite” → “-ous acid” “-ide” → “hydro-____-ic acid” perchloric acid hypochlorous acid sulfuric acid hydrocyanic acid hydrochloric acid nitric acid Practice Naming Acids What are the names of acids formed from the nitrite and nitrate ions? Ex: HNO2 is nitrous acid HNO3 is nitric acid What are the names of acids formed from sulfite and sulfate ions? Ex: H2SO3 is sulfurous acid H2SO4 is sulfuric acid Practice CaSO4 calcium sulfate AlCl3 CrF2 aluminum chloride chromium(II) fluoride CO2 carbon dioxide HCN hydrocyanic acid K2O2 potassium peroxide N2O4 KClO3 NiBr2 dinitrogen tetroxide potassium chlorate nickel(II) bromide LiCl lithium chloride MgO P2O5 magnesium oxide diphosphorus pentoxide Ag3PO4 silver phosphate CH4 methane Fe2O3 iron(III) oxide PRACTICE SITES • Matching nomenclature http://www.zerobio.com/drag_gr9/chem.ht m THE END