Chemical Formulae

1. Chemical Formulae • symbols, naming, writing formulae

2. 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!

3. Some basicscations 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 • monatomicions - single atom with a charge • polyatomicions - several atoms covalently bonded but possessing an overall charge

4. Monatomic NamingCations • 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

5. Monatomic NamingCations • 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+)

6. Monatomic NamingAnions • 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).

7. Monatomic NamingAnions • CAUTION (monatomic anions) • nitrogen, hydrogen, oxygen, and phosphorus lose the last two syllables before adding “-ide” • oxide is O2- and peroxide is O22-

8. 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

9. 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

10. 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

11. Chemical Symbols • combo of symbols that represent the composition of the compound • indicates the elements present and the relative numbers of each element (subscripts)

12. 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

13. 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

14. 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)

15. 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

16. 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

17. 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

18. 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

19. Molecular Compoundsbinary 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

20. 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)

21. Binary Molecular Compounds • Greek prefixes • Oftentimes, the final vowel of prefix is dropped for ease in pronunciation (i.e. heptaoxide and heptoxide)

22. 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

23. 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

24. 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!)

25. 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

26. Organic Compounds • IUPAC Hydrocarbon Prefixes

27. 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

28. Organic Compounds • Examples: write the formula of the following • octyne: C8H14 • methane: CH4(understood 1 for C)

29. 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

30. 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!