1. C HEMICAL F ORMULAS AND COMPOUNDS Chp 7

2. I. C HEMICAL F ORMULAS AND C OMPOUNDS A. Chemical Names and Formulas 1. Monatomic Ions a. Gaining or losing electrons from ions with noble-gas configurations b. Ions formed from a single atom c. Naming 1) Cations – use elements name K + = Potassium cation Mg 2+ = Magnesium cation

3. 2) Anions – ending dropped, add –ide Fluorine – Fluoride (F - ) Nitrogen – Nitride (N -3 ) 2. Binary Ionic Compounds a. Have 2 different elements b. + charges must = neg. charges Mg +2 and Br - MgBr 2

4. What is the formula for combining hydrogen and oxygen? H + and O -2 H2OH2O What is the formula for combining sodium and chlorine?Na + and Cl - NaCl What is the formula for combining Aluminum and oxygen? Al +3 and O -2 (2 x 3+ = 6+) and (3 x -2 = -6) Al 2 O 3

5. 3. Naming Binary Ionic Compounds a. Cation given first b. Name of anion second c. Drop ending and add – ide Al 2 O 3 = Aluminum Oxide ZnO = Zinc oxide AgCl = Silver chloride CaBr 2 = SrF 2 =

6. d. Elements with roman numerals behind them 1) Roman numeral represents positive charge 2) Iron(II) = Fe+2 Iron(III) = Fe+3 4. Naming Binary Molecular Compounds a. Have covalent bonds b. Uses Prefixes

7. NumberPrefix 1Mono - 2Di – 3Tri - 4Tetra - 5Penta - 6Hexa - 7Hepta - 8Octa - 9Nona - 10Deca -

8. c. Less electronegative element is first – give prefix only if there is more than one d. Add prefix to second element e. Add –ide f. Drop o or a of prefix if element starts with a vowel N 2 O – Dinitrogen monoxide NO – Nitrogen monoxide NO 2 – Nitrogen dioxide

9. Assignment pg 213

10. 5. Acids and Salts a. Binary acids – 2 elements, usually hydrogen and a halogen b. Oxyacids – have H, O, and a 3 rd element (usually nonmetal) c. Acid usually refers to a solution in water 1) Hydrogen = hydro 2) Drop ending add –ic 3) Table 7-5 pg 214 (know first column)

11. d. Salt – composed of a cation and anion from an acid

12. B. O XIDATION N UMBERS 1. Distribution of electrons among bonded atoms 2. Assigning Oxidation Numbers a. Shared electrons are assumed to belong to the more-electronegative atom in each bond b. Pure elements have oxidation number of zero c. Sum of oxidation numbers of all atoms in neutral compound is zero

13. Examples Na = 0 O 2 = 0 S 8 = 0 F -1 Na +1 = NaF = 0 H +1 O -2 = H 2 O = 0

14. C. U SING C HEMICAL F ORMULAS 1. Formula mass (Sample prob. 7-6 pg 222) a. Equal to molar mass b. Unit is amu 2. Molar mass a. How many grams are in 1 mole b. Unit = g/mol

15. 3. Percentage Composition a. How to know percentage by mass of a particular element in a chemical compound b. Mass of element in 1mol compound Molar mass of compound X 100%

16. c. Examples What is the percent composition of Cu 2 S? Find molar mass of compound 159.2 g Cu 2 S Find molar mass of each element 2 mol Cu x (63.55g Cu / 1mol Cu) 1 mol S x (32.07g S / 1mol S) Put numbers into formula (127.1g Cu/159.2g Cu 2 S) x100 = 79.84%Cu (32.07g S/159.2 Cu 2 S) x 100 = 20.14% S Check answer: add %s and it should = 100

17. What is the percent composition of hydrogen and oxygen in water? What is the percent composition of oxygen in KClO 3 ?

18. D. D ETERMINING C HEMICAL F ORMULAS 1. Calculations of empirical formulas a. Change % to grams b. Assume you have 100g 1) Diborane is 78.1% B and 21.9% H 2) Contains 78.1 g B and 21.9g H c. Convert grams to moles for each element d. Change to smallest molar ratio

19. 7.22 mol B/7.22 21.7 mol H/7.22 1 mol B to 3.01 mol H = 1mol B to 3 mol H Example 7-12 An analysis shows that a compounds contains 32.38% Na, 22.65% S, and 44.99% O. Find the empirical formula.