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Chemical Formulae symbols, naming, writing formulae Symbols and Formulae 118 known elements ten million known compounds elements - represented by chemical symbols (periodic table) compounds - represented by combos of chemical symbols so we need a very concise naming system! Some basics cations vs anions ions - electrically charged particle usually obtained from an atom by adding or removing electrons anion - negatively charged particle gains/adds electrons cation - positively charged particle loses/removes electrons monatomic ions - single atom with a charge polyatomic ions - several atoms covalently bonded but possessing an overall charge Monatomic Naming Cations You should remember or revisit monatomic naming handouts cations are named by naming the element followed by the word “ion” (i.e. calcium ion) specific charges can be found on the periodic table (see handout) transition metals (gray boxes on handout) require Roman numerals because these elements have multiple oxidation numbers (charges): value of charge = oxidation number Monatomic Naming Cations CAUTION Silver ion is always 1+ and does not require a Roman numeral Mercury (1) is Hg2+2 Mercury (II) Hg2+ Boron ion is B3+ Two polyatomic cations: ammonia (NH3+) and hydronium (H3O+) Monatomic Naming Anions There are monatomic anions and polyatomic anions Monatomic anions are named by naming the element, dropping the ending, and replacing with “-ide.” Charges can be determined from the periodic table (see handout). Monatomic Naming Anions CAUTION (monatomic anions) nitrogen, hydrogen, oxygen, and phosphorus lose the last two syllables before adding “-ide” oxide is O2- and peroxide is O22- Polyatomic Anions Polyatomic anions require a little work (see handout) PLEASE learn the patterns for each group; they are clearly explained to you in the handout titled “Polyatomic Anions: The fifth level of the inferno” If you know the “-ate” form of one member of each group you will be able to determine the other forms Suffix General number of oxygen atoms per- whatever -ate 1 more oxygen than “-ate” whatever -ate usually the most common form whatever -ite 1 less oxygen than “-ate” hypo- whatever -ite 1 less oxygen than “-ite” Polyatomic Anions There are special cases of polyatomic ions that must be memorized, no trends! (see handout - 7th level) acetate, cyanate, cyanide, hydroxide, oxalate, peroxide Polyatomic Anions Sometimes there are prefixes with the polyatomic ions, this is memorization of prefix meanings bi- and hydrogen: hydrogen ion (H+) is added and charge of polyatomic is changed dihydrogen: two hydrogen ions are added and charge is changed di-: two polyatomic ions bonded AND one oxygen atom is lost in the process (charge remains the same) thio-: replace an oxygen with a sulfur Chemical Symbols combo of symbols that represent the composition of the compound indicates the elements present and the relative numbers of each element (subscripts) Oxidation Numbers predict oxidation number (charge on an atom) based on stability to determine the ratio of elements in a compound when writing a chemical formula is to add charges algebraically to equal zero Ionic Compounds compound/formula unit composed of cations and anions positive ion is ALWAYS written first gives the smallest possible integer number of different ions parentheses enclose polyatomic ions when subscript is greater than one ionic substances are electrically neutral Ionic Compounds Examples: Write the ionic compound that results from the combination of the following • calcium and bromine: Ca2+ and Br- : CaBr2 •we need two bromines to balance the positive two charge of calcium • aluminum and sulfate: Al3+ and SO42-: Al2(SO4)3 •we need two aluminums (@ 3+ each) to balance the three sulfates (@ 2- each) Ionic Compounds Shortcut: Cross-and-Drop Method charge of cation becomes subscript of anion charge of anion becomes subscript of cation • Examples: Write the ionic compound that results from the combination of the following • chromium and oxygen: Cr3+ and O2- • Cr3+ O2-: Cr2O3 Ionic Compounds Naming ionic compounds: name of metal followed by anion name Examples: CaBr2 calcium bromide CaCl2 calcium chloride Al2(SO4)3 aluminum sulfate Cr2O3 chromium oxide SrO strontium oxide Try these... Write the formula and name of the ionic compound that would result from the combination of the following ions • 1. K+ CrO42• 2. Ca2+ O2- • 3. Pb4+ Cr2O72• solutions: •1. K2CrO4, potassium chromate •2. CaO, calcium oxide •3. Pb(Cr2O4)2, lead(IV) dichromate Try these... Write the ionic formula given the name of the compound • 1. iron(II) phosphate • 2. titanium (IV) oxalate • 3. thallium (III) nitrate •solutions: •1. Fe3(PO4)2 •2. Ti(C2O4)2 •3. Tl(NO3)3 Molecular Compounds binary and organic molecule - name given to covalently bonded compounds; formed by neutral elements combining diatomic molecules - made of two atoms of the same element; there are 7 and they create a 7 on the periodic table (hydrogen does not help make the “7” due to placement) • H2, N2, O2, F2, Cl2, Br2, I2 Binary Molecular Compounds molecule composed of two elements; usually two nonmetals, two metalloids, or a nonmetal and metalloid naming: use a prefix system •1. name first element using exact element name •2. name second element by writing stem of the name with the “-ide” ending •3. add a Greek prefix to each element name to denote the subscript of each element in formula •(mono- is not usually used, unless needed to distinguish two compounds of the same two elements, CO2 and CO) Binary Molecular Compounds subscript 1 2 Greek prefixes 3 4 Oftentimes, the final 5 vowel of prefix is dropped 6 for ease in pronunciation 7 (i.e. heptaoxide and heptoxide) 8 9 10 prefix monoditritetrapentahexaheptaoctanonadeca- Binary Molecular Compounds Examples: •N2O3: dinitrogen trioxide •P4O6: tetraphosphorus hexoxide •N2O4: dinotrogen tetroxide •SF6: sulfur hexafluoride •*note: the subscripts do not need to be the simplest ratio for molecular compounds Try these… Write the formula or name the following: • 1. Cl2O7 • 2. disulfur trichloride • 3. SO3 • 4. CO2 • 5. carbon disulfide • 6. CO • solutions: 1. dichlorine hetpoxide; 2. S2Cl3; 3. sulfur trioxide; 4. carbon dioxide; 5. CS2; 6. carbon monoxide Organic Molecular Compounds (usually called just organic compounds) organic compounds - molecular substances that contain carbon combined with other elements (H, O, N…) hydrocarbons - organic compounds that consist of only carbon and hydrogen (hence the name!) Organic Compounds naming hydrocarbons • 1. count the number of carbon atoms in the chain and select the appropriate stem (see next slide) • 2. add a suffix to indicate how the carbon atoms are attached (single, double, or triple bonds) •-ane (single bonds) CnH2n+2; n = number of carbon atoms, number of hydrogen atoms is 2n+2 •-ene (double bond) CnH2n; n = number of carbon atoms, number of hydrogen atoms is 2n •-yne (triple bond) CnH2n-2; n = number of carbon atoms, number of hydrogen atoms is 2n-2 • 3. combine prefix and suffix Organic Compounds IUPAC Hydrocarbon Prefixes # of carbon atoms prefix 1 meth- 2 eth- 3 prop- 4 but- 5 pent- 6 hex- 7 hept- 8 oct- 9 non- 10 dec- 11 undec- 12 dodec- 20 iscos- Organic Compounds Example: name the following • C6H14 •1. C: 6 = hex •2. H: 14 = 2n+2 = ane •3. hexane • C3H6 •1. C: 3 = prop •2. H: 6 = 2n = ene •3. propene Organic Compounds Examples: write the formula of the following •octyne: C8H14 •methane: CH4 (understood 1 for C) Try these... Write the name or formula for the following: • 1. C12H24 • 2. nonane • 3. C20H42 • 4. ethene • solutions: 1. dodecene; 2. C9H20; 3. icosane; 4. C2H4 Please Practice There are several worksheets posted on moodle with solutions, please take some time to review naming concepts! Please let me know of any difficulties or issues with this Keynote, PowerPoint, or PDF (whichever you select), thanks!