Chapter 3: Chemical Compounds

1. RVCC Fall 2009 CHEM 103 – General Chemistry I Chapter 3:Chemical Compounds Chemistry: The Molecular Science, 3rd Ed. by Moore, Stanitski, and Jurs

2. Chemical Compounds Pure Substance Molecular Formula Formula Unit

3. Main group metal Transition metal Metalloid Nonmetal

4. Chemical Formulas The chemical formula is a notation using atomic symbols to show the number and kinds of atoms in a substance. Subscript – used to show the numbers of each type of atom. The number applies only to the atom or () that immediately precedes it. C12H22O11 orMg3(PO4)2 Superscript – used to show the charges on ions. Al+3 Coefficients – used to show the number (or moles) of molecules or formula units. The number applies to all that follow it. 2Cl- or 2Ca(OH)2 or 2C6H6 Hydrates – used to show the number of water molecules included. CuSO45H2O

5. Chemical Formulas • Molecular Compound – 2 non-metals (C6H2) • Molecular Formula– a formula that expresses the number of atoms for each element in one molecule of a compound. C6H6 • Structural – the formula written in a way that shows all the connections between atoms in a molecule. • Empirical – a formula showing the simplest possible ratio of atoms of elements in a compound. CH • Ionic Compound – metal and non-metal (NaCl) • Formula Unit– the simplest cation-anion grouping represented • in the formula. Na+Cl- • Empirical – same as formula unit

6. Molecular Compoundsnon-metals Molecular formula • shows the number and kind of elements (but not how they are connected) e.g. water H2O ammonia NH3 benzene C6H6 hydrazine N2H4

7. H | H | H | H | H – C – C – O – H H – C – O – C – H | H | H | H | H dimethyl ether ethanol Molecular Compounds • A structural formulashows how the atoms are connected. Molecules could have the same formulas but different structures. Two structural formulas for C2H6O:

8. Naming Binary Molecular CompoundsNonmetal + Nonmetal • Binary - only two elements (nonmetals). • In binary molecular compounds, the more metallic element is listed first. Increasing metallic character Increasing metallic character

9. Naming Binary Molecular CompoundsNonmetal + Nonmetal (prefix) name of the first nonmetal + (prefix) name of the second nonmetal with “-ide” ending PCl5 – phosphorus pentachloride Prefixes mono = 1 hexa = 6 di = 2 hepta = 7 tri = 3 octa = 8 tetra = 4 nona = 9 penta =5 deca = 10 -ide endings Oxygen - ox + ide = oxide Chlorine - chlor + ide = chloride Hydrogen – hydr + ide = hydride Nitrogen – nitr + ide = nitride Sulfur – sulf + ide = sulfide Phosphorus – phosph + ide = phosphide

10. CO → SO2 → P2O5 → S2Cl2→ CS2→ Naming Binary Molecular CompoundsNonmetal + Nonmetal carbon monoxide sulfur dioxide diphosphorus pentoxide disulfur dichloride carbon disulfide • Never use the prefix mono- for the first element in a name. • If the second element is oxygen, drop the vowel on the prefix. • Do not reduce a molecular formula to smallest whole number ratio.

11. Practice Name the following compounds or give the correct molecular formula: • Tetraphosphorus decoxide • CCl4 • P2N5 • Sulfur trioxide • NO • BF3 • Silicon disulfide • SeH2 P4O10 Carbon tetrachloride Diphosphorus pentanitride SO3 Nitrogen monoxide Boron trifluoride SiS2 Selenium Hydride

12. Ionic Compoundmetal (cation, +) + non-metal (anion, -) An ion is an electrically charged particle obtained from an atom or bonded group of atoms by adding or removing electrons. • When an atom loses an electron it becomes a positively charged - cation • When an atom gains an electron it becomes a negatively charged - anion

13. NaCl “table salt” In ionic solids, cations and anions are held in a regular array: the crystal lattice. This structure determines many of the properties of ionic compounds.

14. Formation of Ionic Compound e- transfer from metal to non-metal Na+1Cl-1 M + Y M+Y- The ionic bond is a strong electrostatic attraction. Na Na+1 Cl Cl-1

15. Monatomic Charges KNOW ! e- loss = Group # e- gained, Group #-8 +1 +2 +3 -4 -3 -2 -1 post-transition

16. Ionic Compounds Total + and – charges are always balanced. Ionic compounds are always neutral! Ions Compound Charges Ca2+ and F- CaF2 1 (2+) + 2(1-) = 0 Ca2+ and O2- CaO 1(2+) + 1(2-) = 0 Ca2+ and N3- Ca3N2 3(2+) + 2(3-) = 0

17. Al Cl 3+ 1- 1 3 Al P 3+ 3- 3 3 Al S 3+ 2- 2 3 metal non-metale- loss = e- gain, net charge=0 Al2O3 →2 (3+) + 3 (2-) = 0 6e- loss 6e- gain Al O 3+ 2- 2 3 aluminum + chlorine aluminum + phosphorus sodium + sulfur AlCl3 AlP Al2S3

18. Naming Binary Ionic CompoundsMetal + Nonmetal name of the metal + modified name of the nonmetal CaF2 – calcium fluoride We do not use prefixes for binary ionic compounds! http://www.chemmybear.com/gcch07sc.pdf

19. Naming Binary Ionic CompoundsMetal + Nonmetal name of the metal + name of a nonmetal “–ide” ending (no prefixes!) NaCl → KBr → LiI → MgBr2 → Na2O → Al2O3→ sodium chloride potassium bromide lithium iodide magnesium bromide sodium oxide aluminum oxide

20. Naming Binary Ionic CompoundsMetal + Nonmetal KNOW! Transition Metals In Sn Pb and post-transition metals FeO – Fe2O3 – iron (II) oxide iron (III) oxide Indicate the charge of the transition metal in the name (with Roman numerals).

21. Naming Compounds with Transition Metals FeCl2 FeCl3 CuO Cu2O CrS Cr2S3 Iron (II) chloride Iron (III) chloride Copper (II) oxide Copper (I) oxide Chromium (II) sulfide Chromium (III) sulfide

22. Practice • ZnCl2 • copper(I) oxide • silver chloride • PbI2 • PbO2 • Cobalt(III) sulfide Zinc chloride Cu2O AgCl Lead(II) iodide Lead(IV) oxide Co2S3

23. Polyatomic Ions • a group of two or more atoms with a net electrical charge If several nonmetal atoms are combined into a polyatomic anion (SO42-)and this anion is combined with a metal cation (Ca2+) the compound will be ionic CaSO4 “calcium sulfate” name of the metal + name of polyatomic ion

24. Know these Polyatomic Ions and their charges! Table 3-7, p.91 SCN- thiocynate CrO4-2 chromate O2-2 peroxide

25. Oxyanions

26. Names and Formulas with polyatomic anions

27. Write formulas for the underlined ionic compounds #1? Ingredients: Menthol, Ammonium Hydroxide, Carbomer 934, Copper (II) Sulfate, FD&C Blue No. 1, isopropyl alcohol, magnesium sulfate, sodium hydroxide, Thymol, water. glass cleaner #2? Ingredients: Triclosan (active ingredient), water, sodium laureth sulfate, ammonium sulfate, decyl glucoside, coamidopropyl betaine, glycerin, sodium chloride, PEG-18 gyceryl oleate/cocoate, fragrance, DMDM Hydantoin, tetrasodium EDTA, citric acid, yellow %, red 4. hand soap

28. Naming Compounds Metallic element in a formula? … the compound is ionic. All non-metal formula? … the compound is molecular. Metalloid in a formula? … no easy way to tell if ionic or molecular.

29. Properties of Molecular & Ionic Compounds

30. Definitions Electrolyte: Dissociates fully or partially into ions when dissolved in a solvent, producing a solution that conducts electricity. Strong electrolyte:It is a solute that completely dissociates into ions in solution. Most soluble ionic compounds are strong electrolytes. Weak electrolyte: It is a solute that incompletely dissociates into ions in solution.

31. Ions in Aqueous Solution(strong electrolyte) 100% H2O (l) +

32. Ions in Aqueous Solution(weak electrolyte) dimmer

33. Sucrose in Solution (non-electrolyte) C12H22O11(s) + H2O (l) C12H22O11(aq)

34. Determining Chemical Formulas The percent composition is the percent by mass of each element present in a compound. • Percent composition or mass percent (or mass percentage) can be referred to: • a component in a mixture • an element in a compound. % = part x 100 whole

35. Mass % from Chemical Formulas Example 1 Calculate the percent of carbon and hydrogen in butane, C4H10. 4 moles of carbon × 12.01g/mol = 48.04 g + 10 moles of hydrogen × 1.01 g/mol = 10.10 g Total mass of 1 mol of C4H10 = 58.14 g

36. Mass Percentages from Formulas Hints: 1 –write the chemical formula of the molecule 2 – evaluate the mass percent of each element

37. Mass % from Formulas

38. Chemical Formulas from Mass % • We just saw how to calculate the percent composition by mass of a compound if we know its formula. Now… Mass percentage Empirical formula “% to mass, mass to mol, divide by smallest, multiply til whole”

39. Chemical Formulas from Mass Example 1 A sample of compound consisting of oxygen and sulfur and weighing 83.5g contains 33.4 g of sulfur. What is the empirical formula of this compound? SxOy Mass of Oxygen? 83.5g - 33.4g = 50.1 g oxygen ‘mass to mol’

40. Determining Chemical Formulas S 1.041/1.041 = 1.000 ‘divide by smallest’ O 3.131/1.041 = 3.007 ‘already multiply ‘til whole’ SO3

41. Chemical Formulas from Mass % Example 2 • Benzoic acid is a white, crystalline powder used as a food preservative. The compound contains 68.8% C, 5.0% H, and 26.2% O by mass. What is its empirical formula? • We want to find the smallest whole-number • ratio of the subscripts in the formula CxHyOz

42. Practice • What is the empirical formula for a compound that is 24.7 % calcium, 1.2 % hydrogen, 14.8 % carbon, and 59.3 % oxygen? For an ionic compound, the empirical formula ≡ the chemical formula. CaC2H2O6 --> Ca(HCO3)2 calcium bicarbonate

43. Chemical Formulas from Mass % • An empirical formula gives the smallest whole-number ratio of atoms or moles of atoms in a formula. • For an ionic compound, the formula is equal to the empirical formula (already smallest whole-number ratio). • For a molecular compound, the molecular formula could be a multiple of the empirical formula. To determine the “true” molecular formula, we must know the molar mass of the compound. • C6H6 -molecular CH -empirical

44. Determining Molecular Formulas C6H6 Empirical formula Molecular formula CH 78.12 30.08 75.10 13.02 15.04 75.10 6X 3X 1X determined empirical formula /empirical mass C2H6 CH3 given molecular mass C3H7O2 C3H7O2 Mass Factor

45. Determining Molecular Formulas Example 3 A compound is 39.9% C, 6.70% H and 53.4% O. The molar mass of this compound is 60.0 g/mol. Determine the molecular formula of this compound. CxHyOz 1st evaluate the empirical formula 3.322 mol 6.634 mol 3.338 mol

46. Determining Molecular Formulas CH2O The molar mass for the empirical formula is 12.01g/mol + 2 x 1.01 g/mol + 16.00g/mol = 30.02g/mol The molecular formula is C2H4O2

47. Determining Molecular Formulas • a) 2-methyl propene is used to make synthetic rubber. A sample contains 84.09% carbon and 15.9% hydrogen. Determine the empirical formula. C4H9 (empirical mass=57.13g/mol b) What is the molecular formula for this compound if it has a molar mass of 57.13? C4H9 • a) What is the empirical formula for dimethylhydrazine, the fuel used in Apollo lunar descent module, if the composition is 39.95% carbon, 13.44 hydrogen and 46.61% nitrogen? CH4N (empirical mass = 30.06g/mol) b) What is the molecular formula for this compound if it has a molar mass of 60.10 g? C2H8N2

48. Name to FormulaFormula to Name • Telephone – ionic and molecular • Flash cards- polyatomic ions • Test Review

49. Summary Problem – Ch.3 During each launch of the Space Shuttle, the booster rocket uses about 1.5 x106 lb of ammonium perchlorate as fuel. • 1. Write the chemical formulas for ammonium perchlorate, ammonium chlorate and ammonium chlorite. • 2. a) When ammonium perchlorate dissociates in water, what ions are dispersed in the solution? b) Would this aqueous solution conduct an electric current? Explain your answer. • 3. How many moles of ammonium perchlorate are used in Space Shuttle booster rockets during a launch. 2.205 lb = 1 kg

50. Summary Problem – Ch. 2 The atoms of one of the elements contain 78 protons and 117 neutrons. • Identify the element and give its symbol. • What is this atom’s atomic number? Mass number? • How many p, n, e does the +4 cation of this element have? • This element has five naturally occurring isotopes 191.9614 (0.79%), 193.9628 (32.9%), 194.9648 (33.8%), 195.9650(25.3%), 197.9675 (7.2%). Calculate the atomic weight of the element.