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Elements and Compounds

Elements and Compounds. elements combine together to make an almost limitless number of compounds the properties of the compound are totally different from the constituent elements H 2 (g) + O 2 (g)  H 2 O(l). Formation of Water from Its Elements.

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Elements and Compounds

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  1. Elements and Compounds • elements combine together to make an almost limitless number of compounds • the properties of the compound are totally different from the constituent elements • H2(g) + O2(g)  H2O(l) Tro, Chemistry: A Molecular Approach

  2. Tro, Chemistry: A Molecular Approach

  3. Tro, Chemistry: A Molecular Approach

  4. Formation of Water from Its Elements Tro, Chemistry: A Molecular Approach

  5. Allotropes:one of two or more forms of an element that differ in their basic structure diamond graphite Tro, Chemistry: A Molecular Approach

  6. Allotropes of carbon diamond graphite Tro, Chemistry: A Molecular Approach

  7. Allotrope of carbon

  8. Chemical Bonds • compounds : made of atoms held together by chemical bonds • Bonds:forces of attraction between atoms • attractions between protons and electrons Tro, Chemistry: A Molecular Approach

  9. Bond Types • two general types of bonding ionic and covalent • ionic bonds electrons transferred between atoms, results in oppositely charged ions that attract each other • Metals + nonmetal • covalent bonds two atoms share some of their electrons • Nonmetal + nonmetal Tro, Chemistry: A Molecular Approach

  10. Molecular View of Elements and Compounds Tro, Chemistry: A Molecular Approach

  11. Homonuclear vs heteronuclear Tro, Chemistry: A Molecular Approach

  12. 7A 7 H2 N2 O2 F2 Cl2 Br2 I2 Molecular Elements • Certain elements occur as 2 atom molecules • Rule of 7’s • Other elements occur as polyatomic molecules • P4, S8, Se8 Tro, Chemistry: A Molecular Approach

  13. Classifying Materials • atomic elements = Fe • molecular elements = N2 • molecular compounds = H2O • ionic compounds = SrCl2 MgCO3 Tro, Chemistry: A Molecular Approach

  14. Representing Compoundswith Chemical Formula • compounds represented with: chemical formula • Type of formula determines amount of information given

  15. Types of FormulaEmpirical Formula • Empirical Formula • Tells atoms and their ratio • do not describe how many atoms, the order of attachment, or the shape • the formulas for ionic compounds are empirical

  16. Empirical formula Empirical formula Molecular formula H2O2 C8H8 C6H12O6 _________ Hg2Cl2 • HO • __________ • __________ • H2O • __________

  17. Types of Formula

  18. Expanded structural formula vs. condensed structural formula

  19. Formula Mass • the mass of an individual molecule or formula unit (FW) amu (D for Dalton) • molecular mass or molecular weight (MW or μ) g/mol • sum of the masses of the atoms in a single molecule or formula unit mass of 1 molecule of H2O = 2(1.01 amu H) + 16.00 amu O = 18.02 amu Tro, Chemistry: A Molecular Approach

  20. What Is a Mole? Tro, Chemistry: A Molecular Approach

  21. How Big is a Mole? • N=6.022x1023 • One mole of Marshmallows would cover the entire earth 12 miles high • One mole of marshmallows would fill the Grand Canyon and still be enough left over to displace all the water from Lake Michigan and more

  22. Mole = 6.022x1023itemsAvogadro’s number N

  23. Molar Mass of Compounds • the relative masses of molecules can be calculated from atomic masses Formula Mass = 1 molecule of H2O = 2(1.01 amu H) + 16.00 amu O = 18.02 amu • since 1 mole of H2O contains 2 moles of H and 1 mole of O Molar Mass = 1 mole H2O = 2(1.01 g H) + 16.00 g O = 18.02 g so the Molar Mass of H2O is 18.02 g/mole Tro, Chemistry: A Molecular Approach

  24. Moles as Conversion factors • Moles to molecules or atoms • Use Avogadro’s number • Ex: How many molecules of water are in 9.01 g of water? • Grams to moles • Use Molar Mass • Ex: How many moles are in 9.01 g of water?

  25. Moles • How many molecules of Chlorine are in 19.5 grams of chlorine? • How many moles of sodium atoms is 29.0 grams of sodium? Tro, Chemistry: A Molecular Approach

  26. Tro, Chemistry: A Molecular Approach

  27. Molecular formula • In 5.0 moles of the compound Mg(H2PO4)2 • How many moles of Mg are there?____ • How many moles of phosphorus are there?___ • How many moles of oxygen are there?______ Tro, Chemistry: A Molecular Approach

  28. Molar mass • What is the formula weight (FW) of Mg(H2PO4)2 including units? ________ • What is the molar mass (MW or µ) of Mg(H2PO4)2 including units?_________ Tro, Chemistry: A Molecular Approach

  29. Practice - Converting Grams to Molecules How many molecules are in 50.0 g of PbO2? (PbO2 = 239.2 g/mol) Tro, Chemistry: A Molecular Approach

  30. Percent Composition • Percentage of each element in a compound • Mass of element/mass of compound • The percentages may not always total to 100% due to rounding Tro, Chemistry: A Molecular Approach

  31. C=12.01, Cl=35.45, F=19.00 Find the mass percent of Cl in CCl2F2

  32. Mass Percent as a Conversion Factor • the mass percent tells you the mass of a constituent element in 100 g of the compound • the fact that CCl2F2 is 58.64% Cl by mass means that 100 g of CCl2F2 contains 58.64 g Cl • this can be used as a conversion factor • 100 g CCl2F2: 58.64 g Cl

  33. g Na g NaCl Example 3.14 – Find the mass of table salt containing 2.4 g of Na 2.4 g Na, 39% Na g NaCl Given: Find: 100. g NaCl : 39 g Na Concept Plan: Relationships: Solution: Check: since the mass of NaCl is more than 2x the mass of Na, the number makes sense

  34. Benzaldehyde is 79.2% carbon. What mass of benzaldehyde contains 19.8 g of C?

  35. Empirical Formula • simplest, whole-number ratio of the atoms of elements in a compound • can be determined from elemental analysis • masses of elements formed when decompose or react compound • combustion analysis • percent composition Tro, Chemistry: A Molecular Approach

  36. Finding an Empirical Formula • convert the percentages to grams • assume you start with 100 g of the compound • skip if already in grams • convert grams to moles • use molar mass of each element • write a pseudoformula using moles as subscripts • divide all by smallest number of moles • if result is within 0.1 of whole number, round to whole number • multiply all mole ratios by number to make all whole numbers • if ratio ?.5, multiply all by 2; if ratio ?.33 or ?.67, multiply all by 3; if ratio 0.25 or 0.75, multiply all by 4; etc. • skip if already whole numbers Tro, Chemistry: A Molecular Approach

  37. Calculating Empirical formula • 1. A sample of an unknown compound with a mass of 2.571 g was found to contain 1.102 g of carbon and 1.469 g of oxygen. What is its empirical formula?

  38. Calculating empirical formula • An oxide of iron called black iron oxide, is analyzed. In a 2.448 g sample the ore was found to contain 1.771 g of Fe and 0.6766 g of O. Calculate the empirical formula of this compound

  39. Example 3.17 • Laboratory analysis of aspirin determined the following mass percent composition. Find the empirical formula. C = 60.00% H = 4.48% O = 35.53%

  40. Finding empirical formula mol C, H, O mol ratio empirical formula g C, H, O Tro, Chemistry: A Molecular Approach

  41. Determine the empirical formula of hematite, which contains 72.4% Fe (55.85) and the rest oxygen (16.00) Tro, Chemistry: A Molecular Approach

  42. Molecular Formulas • The molecular formula is a multiple of the empirical formula • To determine the molecular formula you need to know the empirical formula and the molar mass of the compound

  43. Example 3.18 – Find the molecular formula of butanedione empirical formula for butanedione = C2H3O; MW of molecular formula = 86.03 g/mol

  44. Benzopyrene has a molar mass of 252 g/mol and an empirical formula of C5H3. What is its molecular formula? (C = 12.01, H=1.01)

  45. hydrates

  46. Hydrates • When the hydrate of RuCl3 is heated water is driven off to form the anhydrous salt as shown below: • RuCl3.xH2O  RuCl3 + xH2O • If 1.056 g of hydrated compound is heated and 0.838 g of anhydrous salt remains what is the value of x?

  47. Naming hydrates: name the ionic compound then the water part, use prefixes for number of water molecules Ionic formula • x H2O x = prefix (di, tri etc from covalent naming) H2O = hydrate Ex:   CuSO4• 5 H2O   copper(II) sulfate pentahydrate Ex.   CaCl2• 2 H2O   calcium chloride dihydrate

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