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CHAPTER 2

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  1. CHAPTER 2 CHEMICAL FORMULAS & COMPOSITION STOICHIOMETRY

  2. Chapter Goals • Atoms and Molecules • Chemical Formulas • Ions and Ionic Compounds • Names and Formulas of Some Ionic Compounds • Atomic Weights • The Mole

  3. Chapter Goals • Formula Weights, Molecular Weights, and Moles • Percent Composition and Formulas of Compounds • Derivation of Formulas from Elemental Composition • Determination of Molecular Formulas • Some Other Interpretations of Chemical Formulas • Purity of Samples

  4. Atoms and Molecules • Dalton’s Atomic Theory - 1808 • Five postulates • An element is composed of extremely small, indivisible particles called atoms. • All atoms of a given element have identical properties that differ from those of other elements. • Atoms cannot be created, destroyed, or transformed into atoms of another element. • Compounds are formed when atoms of different elements combine with one another in small whole-number ratios. • The relative numbers and kinds of atoms are constant in a given compound. • Which of these postulates are correct today?

  5. Atoms and Molecules • A molecule is the smallest particle of an element that can have a stable independent existence. • Usually have 2 or more atoms bonded together • Examples of molecules • H2 • O2 • S8 • H2O • CH4 • C2H5OH

  6. Chemical Formulas • Chemical formula shows the chemical composition of the substance. • ratio of the elements present in the molecule or compound • He, Au, Na – monatomic elements • O2, H2, Cl2 – diatomic elements • O3, S4, P8 - more complex elements • H2O, C12H22O11 – compounds • Substance consists of two or more elements

  7. Chemical Formulas Compound1 Molecule Contains HCl 1 H atom & 1 Cl atom H2O 2 H atoms & 1 O atom NH3 1 N atom & 3 H atoms C3H8 3 C atoms & 8 H atoms

  8. Ions and Ionic Compounds • Ions are atoms or groups of atoms that possess an electric charge. • Two basic types of ions: • Positive ions or cations • one or more electrons less than neutral • Na+, Ca2+, Al3+ • NH4+ - polyatomic cation • Negative ions or anions • one or more electrons more than neutral • F-, O2-, N3- • SO42-, PO43- - polyatomic anions

  9. Ions and Ionic Compounds • Sodium chloride • table salt is an ionic compound

  10. Names and Formulas of Some Ionic Compounds • Table 2-3 displays the formulas, charges, and names of some common ions • You must know the names, formulas, and charges of the common ions in table 2-3. • Some examples are: • Anions - Cl1-, OH1-, SO42-, PO43- • Cations - Na1+, NH41+, Ca2+, Al3+

  11. Names and Formulas of Some Ionic Compounds • Formulas of ionic compounds are determined by the charges of the ions. • Charge on the cations must equal the charge on the anions. • The compound must be neutral. • NaCl sodium chloride (Na1+ & Cl1-) • KOH potassium hydroxide(K1+ & OH1-) • CaSO4 calcium sulfate (Ca2+ & SO42-) • Al(OH)3 aluminum hydroxide (Al3+ & 3 OH1-)

  12. Names and Formulas of Some Ionic Compounds • Table 2-2 gives names of several molecular compounds. • You must know all of the molecular compounds from Table 2-2. • Some examples are: • H2SO4 - sulfuric acid • FeBr2 - iron(II) bromide • C2H5OH - ethanol

  13. Names and Formulas of Some Ionic Compounds You do it! • What is the formula of nitric acid? • HNO3 • What is the formula of sulfur trioxide? • SO3 • What is the name of FeBr3? • iron(III) bromide

  14. Names and Formulas of Some Ionic Compounds You do it! • What is the name of K2SO3? • potassium sulfite • What is charge on sulfite ion? • SO32- is sulfite ion • What is the formula of ammonium sulfide? • (NH4)2S

  15. Names and Formulas of Some Ionic Compounds You do it! • What is charge on ammonium ion? • NH41+ • What is the formula of aluminum sulfate? • Al2(SO4)3 • What is charge on both ions? • Al3+ and SO42-

  16. Atomic Weights • Weighted average of the masses of the constituent isotopes if an element. • Tells us the atomic masses of every known element. • Lower number on periodic chart. • How do we know what the values of these numbers are?

  17. The Mole • A number of atoms, ions, or molecules that is large enough to see and handle. • A mole = number of things • Just like a dozen = 12 things • One mole = 6.022 x 1023 things • Avogadro’s number = 6.022 x 1023 • Symbol for Avogadro’s number is NA.

  18. The Mole • How do we know when we have a mole? • count it out • weigh it out • Molar mass - mass in grams numerically equal to the atomic weight of the element in grams. • H has an atomic weight of 1.00794 g • 1.00794 g of H atoms = 6.022 x 1023 H atoms • Mg has an atomic weight of 24.3050 g • 24.3050 g of Mg atoms = 6.022 x 1023 Mg atoms

  19. The Mole • Example 2-4: How many moles of Mg atoms are present in 73.4 g of Mg? You do it!

  20. The Mole • Example 2-4: How many moles of Mg atoms are present in 73.4 g of Mg?

  21. The Mole • Example 2-4: How many moles of Mg atoms are present in 73.4 g of Mg?

  22. The Mole • Example 2-4: How many moles of Mg atoms are present in 73.4 g of Mg? IT IS IMPERATIVE THAT YOU KNOW HOW TO DO THESE PROBLEMS

  23. The Mole • Example 2-1: Calculate the mass of a single Mg atom in grams to 3 significant figures.

  24. The Mole • Example 2-1: Calculate the mass of a single Mg atom in grams to 3 significant figures.

  25. The Mole • Example 2-1: Calculate the mass of a single Mg atom in grams to 3 significant figures.

  26. The Mole • Example 2-1: Calculate the mass of a single Mg atom, in grams, to 3 significant figures.

  27. The Mole • Example 2-2: Calculate the number of atoms in one-millionth of a gram of Mg to 3 significant figures.

  28. The Mole • Example 2-2: Calculate the number of atoms in one-millionth of a gram of Mg to 3 significant figures.

  29. The Mole • Example 2-2: Calculate the number of atoms in one-millionth of a gram of Mg to 3 significant figures.

  30. The Mole • Example 2-2: Calculate the number of atoms in one-millionth of a gram of Mg to 3 significant figures.

  31. The Mole • Example 2-3. How many atoms are contained in 1.67 moles of Mg?

  32. The Mole • Example 2-3. How many atoms are contained in 1.67 moles of Mg?

  33. The Mole • Example 2-3. How many atoms are contained in 1.67 moles of Mg?

  34. The Mole • Example 2-3. How many atoms are contained in 1.67 moles of Mg?

  35. The Mole • Example 2-3. How many atoms are contained in 1.67 moles of Mg?

  36. Formula Weights, Molecular Weights, and Moles • How do we calculate the molar mass of a compound? • add atomic weights of each atom • The molar mass of propane, C3H8, is:

  37. Formula Weights, Molecular Weights, and Moles • The molar mass of calcium nitrate, Ca(NO3)2 , is: You do it!

  38. Formula Weights, Molecular Weights, and Moles

  39. Formula Weights, Molecular Weights, and Moles • One Mole of Contains • Cl2 or 70.90g 6.022 x 1023 Cl2 molecules 2(6.022 x 1023 ) Cl atoms • C3H8You do it!

  40. Formula Weights, Molecular Weights, and Moles • One Mole of Contains • Cl2 or 70.90g 6.022 x 1023 Cl2 molecules 2(6.022 x 1023 ) Cl atoms • C3H8 or44.11 g 6.022 x 1023 C3H8 molecules 3 (6.022 x 1023 ) C atoms 8 (6.022 x 1023 ) H atoms

  41. Formula Weights, Molecular Weights, and Moles • Example 2-5: Calculate the number of C3H8 molecules in 74.6 g of propane.

  42. Formula Weights, Molecular Weights, and Moles • Example 2-5: Calculate the number of C3H8 molecules in 74.6 g of propane.

  43. Formula Weights, Molecular Weights, and Moles • Example 2-5: Calculate the number of C3H8 molecules in 74.6 g of propane.

  44. Formula Weights, Molecular Weights, and Moles • Example 2-5: Calculate the number of C3H8 molecules in 74.6 g of propane.

  45. Formula Weights, Molecular Weights, and Moles • Example 2-6. What is the mass of 10.0 billion propane molecules? You do it!

  46. Formula Weights, Molecular Weights, and Moles Example 2-6. What is the mass of 10.0 billion propane molecules?

  47. Formula Weights, Molecular Weights, and Moles • Example 2-7. How many (a) moles, (b) molecules, and (c) oxygen atoms are contained in 60.0 g of ozone, O3? The layer of ozone in the stratosphere is very beneficial to life on earth. You do it!

  48. Formula Weights, Molecular Weights, and Moles • Example 2-7. How many (a) moles, (b) molecules, and (c) oxygen atoms are contained in 60.0 g of ozone, O3? The layer of ozone in the stratosphere is very beneficial to life on earth. (a)

  49. Formula Weights, Molecular Weights, and Moles • Example 2-7. How many (a) moles, (b) molecules, and (c) oxygen atoms are contained in 60.0 g of ozone, O3? The layer of ozone in the stratosphere is very beneficial to life on earth. (b)

  50. Formula Weights, Molecular Weights, and Moles • Example 2-7. How many (a) moles, (b) molecules, and (c) oxygen atoms are contained in 60.0 g of ozone, O3? The layer of ozone in the stratosphere is very beneficial to life on earth. (b)

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