Chapter 7 Chemical Formulas and Names

1. Chapter 7Chemical Formulas and Names Use this power point for reference only. It mentions the textbook topics and has a few good examples, but most notes will be covered without a power point. We will not do oxidation numbers at this time. (11/4/11)

2. 7.1 Chemical Names and Formulas C8H18 8 Carbon atoms 18 Hydrogen Atoms Al2(SO4)3 2 Aluminum atoms 4 Oxygen atoms 3 of everything in ( ) making 3 Sulfur atoms and 12 Oxygen atoms total Chemical Names & Formulas Oxidation Numbers Using Chemical Formulas Determining Chemical Formulas Questions

3. Monatomic Ions :: ions formed from a single atom :: NAMING :: Element Root + -ide F F- Flourine Flouride anion N N3- Nitrogen Nitride anion O2- = ? Chemical Names & Formulas Oxidation Numbers Using Chemical Formulas Determining Chemical Formulas Questions

4. Binary Ionic Compounds Nomenclature :: naming system Naming :: Al2O3 Name of CationName of Anion (with –ide ending) Aluminum Oxide Writing the Formula Chemical Names & Formulas Oxidation Numbers Using Chemical Formulas Determining Chemical Formulas Questions

5. Chemical Names & Formulas Oxidation Numbers Using Chemical Formulas Determining Chemical Formulas Questions

6. Nomenclature :: The Stock System Some elements [such as transition metals] form two or more cations with different charges. The stock system is used to distinguish between the different ions of an element. Fe2+ Iron (II) Fe3+  Iron (III) CuCl2  Cu2+ Cl- Name of Cation + Roman Numeral Name of Anion indicating charge Copper (II) Chloride Chemical Names & Formulas Oxidation Numbers Using Chemical Formulas Determining Chemical Formulas Questions

7. Polyatomic Ions & Oxyanions oxyanions :: polyatomic ions that contain oxygen 1 less O than ___ite has 1 less O than other oxyanion has 1 more O than other oxyanion 1 more O than ___ate ClO- ClO2 ClO3 ClO4 Hypochlorite Chlorite Chlorate Perchlorate Common Polyatomic Ions: NO3- SO42- CO32- PO43- OH- NH4+ Nitrate Sulfate Carbonate PhosphateHydroxide Ammonium Chemical Names & Formulas Oxidation Numbers Using Chemical Formulas Determining Chemical Formulas Questions

8. Binary Molecular Compounds NAMING RULES 1. First element does not take a prefix if it only contributes 1 atom to the compound 2. Second element takes prefix, drop ending, add –ide 3. The o or a at the end of prefix is dropped if the element begins with a vowel PREFIXES # atomsPrefix# atomsPrefix 1 mono- 6 hexa- 2 di- 7 hepta- 3 tri- 8 octa- 4 tetra- 9 nona- 5 penta- 10 deca- P4O10 Prefix [if needed] + Prefix [determined by # Name of element atoms] + root name + -ide Tetraphosphorus decoxide Chemical Names & Formulas Oxidation Numbers Using Chemical Formulas Determining Chemical Formulas Questions

9. Naming Acids Have O ? Yes No Poly atomic ion root + suffix Acid Hydro________ic Acid [Hydro + root + ic Acid] HNO3 Nitric Acid Ex: HCl Hydrochloric acid Nitrate  Nitric Acid HF Hydrofluoric acid HNO2 Nitrous Acid HClO4 Perchloric Acid HClO2 Hypochlorous Acid HClO3 Chloric Acid ACID SUFFIXES Polyatomic Ion suffixAcid suffix - ate [nitrate]  -ic [nitric] -ite [nitrite]  -ous [nitrous] Chemical Names & Formulas Oxidation Numbers Using Chemical Formulas Determining Chemical Formulas Questions

10. 7.2 Oxidation Numbers Oxidation number :: numbers assigned to compound or ion to indicate the general distribution of electrons among the bonded atoms in a molecular compound/ion • Oxidation numbers have no physical meaning Wait, they don’t mean anything?! Then why do we have them?! Oxidation numbers are helpful in naming compounds, writing formulas, and balancing chemical equations [redox!!] Chemical Names & Formulas Oxidation Numbers Using Chemical Formulas Determining Chemical Formulas Questions

11. Rules for Assigning Oxidation Numbers • Atoms in pure element have oxidation number zero (0). • Elements in a binary molecular compound are given oxidations numbers equal to the charges they would have as ions • Flourine always has an oxidation number of -1. • Oxygen has an oxidation number of -2 in every compound except for peroxides (like H2O2), where it is -1, and with halogens, has oxidation number +2 (OF2) • Hydrogen has oxidation number +1 in compounds with elements more electronegative than itself; it has oxidation number -1 in metal compounds • Algebraic sum of oxidation numbers of all atoms in compound add up to charge of compound • Monatomic ions have oxidation numbers equal to their charges. • Rules 1-7 apply to covalently bonded atoms, but oxidation numbers can also be assigned to atoms in ionic compounds. Chemical Names & Formulas Oxidation Numbers Using Chemical Formulas Determining Chemical Formulas Questions

12. Assigning Oxidation Numbers UF6We know that fluorine has oxidation # -1. There are 6 F atoms, so -1 x 6 = -6. Also, the sum of oxidation numbers must equal the charge of the compound, or O, in this case. U + (-6) = 0. Therefore, the Oxidation number of U = +6. Oxidation Number: U: +6 F: -1 ClO3-Oxygen has oxidation # of -2. Total of oxidation numbers must add up to -1. Therefore, Cl has oxidation number of +5. Oxidation Number: Cl: +5 O: -2 Oxidation number S in H2SO4 ?? Answer: +6 Chemical Names & Formulas Oxidation Numbers Using Chemical Formulas Determining Chemical Formulas Questions

13. 7.3 Using Chemical Formulas Formula Mass :: sum of the average atomic masses of all the atoms represented in its formula FOR EXAMPLE : The formula mass for H2O is: Average atomic mass for H : 1.01 amu Average atomic mass of O : 16.00 amu 2 H atoms x 1.01 amu = 2.02 amu 1 O atom x 16.00 amu = 16.00 amu formula mass of H2O = 18.02 amu  Chemical Names & Formulas Oxidation Numbers Using Chemical Formulas Determining Chemical Formulas Questions

14. Molar Mass Is there any difference between molar mass and formula mass ??? OF COURSE. The units are different. But that is the ONLY difference. To change from formula mass to molar mass, change amu to grams. Molar Mass for H2O = ? (Formula mass = 18.02 amu) MM for MgCl2 = ? (Formula mass = 95.21 amu) Chemical Names & Formulas Oxidation Numbers Using Chemical Formulas Determining Chemical Formulas Questions

15. Using Molar Mass as a Conversion The unit of Molar Mass is grams/mol . 1 Mass in grams x -------------------------- = amount in moles molar mass (g/mol) 32 grams of O2 = ? Moles O2 (Formula mass of O = 16 amu) Answer: 1 mole O2 Chemical Names & Formulas Oxidation Numbers Using Chemical Formulas Determining Chemical Formulas Questions

16. Percent Composition Mass of element in sample compound ---------------------------------------------- x 100 = % element in compound mass of sample of compound Or Mass of element in 1 mol of compound ------------------------------------------------ x 100 = % element in compound molar mass of compound Chemical Names & Formulas Oxidation Numbers Using Chemical Formulas Determining Chemical Formulas Questions

17. 7.4 Determining Chemical Formulas Empirical Formula :: symbols for the elements combined in a compound, with subscripts showing the smallest whole-number mole ratio of the different atoms in the compound Example: Empirical Formula: BH3 Molecular Formula: B2H6 Empirical Formula: P2O5 Empirical Ratio: 2 Molecular Formula = ? Answer: P4O10 Chemical Names & Formulas Oxidation Numbers Using Chemical Formulas Determining Chemical Formulas Questions

18. Calculating Empirical Formulas • Assume there is 100g of the compound. • Convert g to moles of each element using it’s molar mass. • Divide all moles by the smallest value of moles. If decimals are present, multiply all by 2 (0.5), 3 (0.3) or 4 (0.25), etc. :: Keep in mind that decimals may be rounded (3.01  3, 1.99  2 and so on) Percent composition of diborane is 78.1% B and 21.9% H. Find it’s empirical formula. 1 mol B 1 mol H 78.1g B x ------------ = 7.22 mol B 21.9 g H x ------------- = 21.7 mol H 10.81g B 1.01 g H 7.22 mol B 21.7 mol H ------------- : ----------------- = 1 mol B : 3.01 mol H  BH3 7.22 7.22 Chemical Names & Formulas Oxidation Numbers Using Chemical Formulas Determining Chemical Formulas Questions

19. Calculating Molecular Formulas Converting empirical formula to molecular formula :: x (empirical formula) = molecular formula X is a whole number multiple indicating the factor by which the subscripts in the empirical formula must be multiplied by to get the molecular formula experimental formula mass 27.67 amu X = ----------------------------------- Ex. X= ------------- = 2 empirical formula mass 13.84 amu Empirical Formula = BH3 Molecular Formula = B2H6 Chemical Names & Formulas Oxidation Numbers Using Chemical Formulas Determining Chemical Formulas Questions

20. ANYQUESTIONS? Chemical Names & Formulas Oxidation Numbers Using Chemical Formulas Determining Chemical Formulas Questions