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CHAPTER 2

CHAPTER 2. CHEMICAL FORMULAS & COMPOSITION STOICHIOMETRY. One drop of water is about 0.05g or 0.05 ml One drop of water contains about 1.67 x 10 21 H 2 O molecules 167,000,000,000,000,000,000 H 2 O molecules 1.67 sextillion H 2 O molecules

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CHAPTER 2

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  1. CHAPTER 2 CHEMICAL FORMULAS & COMPOSITION STOICHIOMETRY

  2. One drop of water is about 0.05g or 0.05 ml One drop of water contains about 1.67 x 1021H2O molecules 167,000,000,000,000,000,000H2O molecules 1.67 sextillion H2O molecules There are about 5 sextillion atoms in a drop of water

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

  4. 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

  5. John Dalton (1766-1844) Atoms and Molecules • Dalton’s Atomic Theory - 1808

  6. 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?

  7. Hydrogen Atom .00000000005 m Atoms • Atom • the smallest particle of an element that maintains its identity through all chemical and physical changes

  8. Although one can subdivide atoms into numerous subatomic particles, we will be concerned only with protons, neutrons and electrons. Protons and neutrons are together in the nucleus of an atom, whereas electrons are in motion in orbits around the central nucleus. Protons carry a positive electrical charge, electrons carry a negative charge, and neutrons carry no charge. Neutrons work to keep nuclei together. Most atoms are electrically neutral, meaning that they have an equal number of protons and electrons. The Stuff That Makes Atoms

  9. The Stuff That Makes Atoms negatively charged Different # of neutrons = isotopes: 12C / 13C / 14C positively charged

  10. Atomic Number • Atomic numeber ( symbol is Z) of an element is defined as the number of protons in the nucleus • atomic number (Z) = # protons in the nucleus • # protons = # electrons (electroneutrality!)

  11. 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

  12. Atoms and Molecules • Examples of molecules

  13. 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, C2H5OH – compounds • Substance consists of two or more elements

  14. Chemical Formulas • monatomic elements

  15. Chemical Formulas • diatomic elements

  16. Chemical Formulas • triatomic elements

  17. Chemical Formulas • H2O, CH3OH – compounds

  18. 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

  19. 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

  20. Ions and Ionic Compounds ion – where the # of protons  the # of electrons cation – where the # of protons > the # of electrons anion – where the # of protons < the # of electrons

  21. Calcium • Most abundant mineral in animal tissues • Lots of functions • Bone structure • Nerve function • Blood clotting • Muscle contraction • Cellular metabolism

  22. Other ions Zinc Oxide Zn2+ Bismuth ion Bi2+

  23. NaCl (common table salt) NaF (toothpaste to fight cavities) Aluminum oxide (Al2O3). The mineral, corundum, is made of aluminum oxide. It is very hard, which is why it's used in sand paper.

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

  25. 13 3+ Al 34 2- Se Do You Understand Ions? How many protons and electrons are in? 13 protons, 10 (13 – 3) electrons How many protons and electrons are in ? 34 protons, 36 (34 + 2) electrons 2.5

  26. 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.

  27. Common Cations (positive ions) Formula Charge Name Na+ 1+ sodium K+ 1+ potassium NH4+ 1+ ammonium Ag+ 1+ silver Mg2+ 2+ magnesium Ca2+ 2+ calcium Zn2+ 2+ zinc Cu+ 1+ copper(I) Cu2+ 2+ copper(II) Fe2+ 2+ iron(II) Fe3+ 3+ iron(III) Al3+ 3+ aluminum

  28. Common Anions (negative ions) Formula Charge Name F - 1- fluoride Cl - 1- chloride Br- 1- bromide OH - 1- hydroxide CH3COO - 1- acetate NO3- 1- nitrate O2- 2- oxide S2- 2- sulfide SO42- 2- sulfate SO32- 2- sulfite CO32- 2- carbonate PO43- 3- phosphate

  29. 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-) • What about aluminum hydroxide?

  30. Names and Formulas of Some Ionic Compounds • To determine the Formula of an ionic compound, you must know the charge of the cation and anion. The relative numbers of the ions are adjusted by adding subscripts so that the total charge of all the ions added together is ZERO. e.g. aluminum hydroxide Al3+ + 3OH- Al(OH)3 charge on ions: (3+) + 3(1-) = 0

  31. Names and Formulas of Some Ionic Compounds potassium sulfate 2K+ + SO42- K2SO4 charge on ions: 2(1+) + (2-) = 0 copper(II) nitrate Cu2+ + 2NO3- Cu(NO3)2 charge on ions (2+) + 2(1-) = 0 iron(II) phosphate 3Fe2+ + 3PO43- Fe3(PO4)2 charge on ions 3(2+) + 2(3-) = 0

  32. 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

  33. 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

  34. 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

  35. 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-

  36. Atomic Weights • Scientists have put together a scale for comparing the masses of all the elements. The units are called amu (atomic mass units) or atomic weight (AW). 1 amu = 1/12 mass of Carbon-12 atom. On this scale: Atomic weight of H (weight of one atom): 1.0079 amu Atomic weight of Na: 22.98977 amu Na atom has 23 times more mass than the H atom The periodic table lists the masses of all the known atoms in amu.

  37. 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?

  38. Z X Element Symbol A Atomic Number 1 1 1 H (T) H (D) H Mass Number 3 2 1 92 92 U U 235 238 ISOTOPES Isotopesare atoms of the same element (X) with different numbers of neutrons in their nuclei Atomic number (Z)= number of protons in nucleus Mass number (A)= number of protons + number of neutrons = atomic number (Z) + number of neutrons 2.3

  39. 6 C How many protons, neutrons, and electrons are in ? 14 6 C How many protons, neutrons, and electrons are in ? 11 Do You Understand Isotopes? 6 protons, 8 (14 - 6) neutrons, 6 electrons 6 protons, 5 (11 - 6) neutrons, 6 electrons 2.3

  40. 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.

  41. 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

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

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

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

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

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

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

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

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

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