1 / 78

CHAPTER 2

CHAPTER 2. CHEMICAL FORMULAS & COMPOSITION STOICHIOMETRY. Chapter Goals. Atoms and Molecules Chemical Formulas Ions and Ionic Compounds Names and Formulas of Some Ionic Compounds Atomic Weights The Mole. Chapter Goals. Formula Weights, Molecular Weights, and Moles

wilmer
Download Presentation

CHAPTER 2

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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 2-1: Calculate the mass of a single Mg atom in grams to 3 significant figures.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

  35. 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

  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 2-8. Calculate the number of O atoms in 26.5 g of Li2CO3. You do it!

  46. Formula Weights, Molecular Weights, and Moles • Example 2-8. Calculate the number of O atoms in 26.5 g of Li2CO3.

  47. Formula Weights, Molecular Weights, and Moles • Occasionally, we will use millimoles. • Symbol - mmol • 1000 mmol = 1 mol • For example: oxalic acid (COOH)2 • 1 mol = 90.04 g • 1 mmol = 0.09004 g or 90.04 mg

  48. Formula Weights, Molecular Weights, and Moles • Example 2-9: Calculate the number of mmol in 0.234 g of oxalic acid, (COOH)2. You do it!

  49. Formula Weights, Molecular Weights, and Moles • Example 2-9: Calculate the number of mmol in 0.234 g of oxalic acid, (COOH)2.

  50. Percent Composition and Formulas of Compounds • % composition = mass of an individual element in a compound divided by the total mass of the compound x 100% • Determine the percent composition of C in C3H8.

More Related