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CHAPTER 2

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CHAPTER 2

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  1. ATOMS AND ELEMENTS CHAPTER 2 • Read Chapter 2. • Study all examples and complete all exercises.

  2. Chapter 2 Outline • Discovery of the three atomic particles • Isotopes • Periodic Table • Groups and Periods

  3. ATOMS AND ELEMENTS 3

  4. Origins of the Atomic Theory • John Dalton-1803 • Law of Conservation of Matter • Law of Definite Proportions Water is always H2O not HO • Law of Multiple Proportions SO2 and SO3

  5. Dalton’s Atomic Theory 1. All matter is composed of atoms. 2. Atoms of an element are alike, atoms of different elements are different. 3. Atoms cannot be created, destroyed, subdivided, or converted into atoms of another element. 4. A compound is formed when different atoms combine in fixed, simple, whole-number ratio. 5. A chemical change is a rearrangement of atoms.

  6. Radioactivity • One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie(1876-1934). • She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces. Alpha, a, mass 4 amu, charge +2 Beta, b, mass 1/1500 amu, charge -1 Gamma, g, no mass, no charge

  7. ATOMIC COMPOSITION • Protons ( p, p+) • + electrical charge • mass = 1.672623 x 10-24 g • relative mass = 1.007 atomic mass units (amu) • Electrons ( e, e-) • negative electrical charge • relative mass = 0.0005 amu • Neutrons ( n, n0) • no electrical charge • mass = 1.009 amu

  8. ATOM COMPOSITION • Protons and neutrons are in the nucleus. • The number of electrons is equal to the number of protons. • Electrons in space around the nucleus. • Atoms are extremely small. • One teaspoon of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of water. The atom is mostly empty space.

  9. Deflection of a Cathode Ray

  10. Thomson’s Charge-to-Mass Experiment

  11. Millikan’s Oil Drop Experiment

  12. Themodern view of the atom was developed byErnest Rutherford(1871-1937).

  13. The Rutherford Experiment

  14. How Large is an Atom? Circle consists of 48 iron atoms. Radius of circle is 71 Angstrom units where 1 A = 1 x 10-8 cm. STM image of “quantum corral” of iron atoms

  15. atomic number (Z) 13 Al symbol 26.9815 atomic weight Atomic Number, Z All atoms of the same element have the same number of protons in the nucleus, Z

  16. Mass Number, A C atom with 6 protons and 6 neutrons is the mass standard = 12 atomic mass units, amu Mass Number = # protons + # neutrons A Boron atom can have A = 5 p + 5 n = 10 B A 10 5 Z

  17. 11B 10B Isotopes • Atoms of the same element (same Z) but different mass number (A). • Boron-10 (10B) has 5 p and 5 n • Boron-11 (11B) has 5 p and 6 n

  18. 202 Hg 80 Check Problems Determine the mass number of a mercury atom with 122 neutrons and give its complete atomic symbol. Determine the number of protons, neutrons, and electrons in a Fe-55 atom. 26 p+, 26 e-, 29 n

  19. Mass Spectrometer

  20. 11B 10B Isotopes • Because of the existence of isotopes, the mass of a collection of atoms has an average value. • Average mass = ATOMIC WEIGHT • Boron is 19.91% 10B and 80.09% 11B. That is, 11B is 80.09 percent abundant on earth. • For boron atomic weight (mass) = 0.1991 (10.01 amu) + 0.8009 (11.01 amu) = 10.811 amu

  21. Solution 1) abundance atomic mass 6Li 7.42% 6.015 amu 7Li 92.58% 7.016 amu What is the atomic weight of Li? (.0742)(6.015 amu) + (.9258)(7.016 amu) .446313 amu + 6.4954… amu 6.941 amu

  22. Practice Problem • Calculate the % abundance for the two isotopes of gallium, given Ga atomic weight is 69.723 amu, and: Ga-69, 68.926 amu; Ga-71, 70.925 amu

  23. Solution 2) Calculate the % abundance for the two isotopes of gallium. Ga-69, 68.926 amu; Ga-71, 70.925 amu 60.13 % 39.87 % x(68.926 amu) + (1-x)(70.925 amu) = 69.723 amu 68.926 x amu 69.723 amu -70.925 x amu -70.925 amu -1.999 x amu = -1.202 amu x = .6013

  24. Periodic Table Lothar Meyer 1869 (1830 – 1895) The periodic table arranges elements according to similar properties Dimitri Mendeleev 1868 (1834 - 1907)

  25. Mendeleev’s 1872 Periodic Table

  26. Periods in the Periodic Table1-7

  27. Groups in the Periodic Table1-18

  28. Group 1: Alkali Metals Reaction of potassium and water K + H2O Cutting sodium metal

  29. Group 2: Alkaline Earth Metals Magnesium Magnesiumoxide

  30. Group 13: B, Al, Ga, In, Tl Boron halides, BF3& BI3 Aluminum

  31. Group 14: C, Si, Ge, Sn, Pb Quartz, SiO2 Diamond

  32. from http://cnst.rice.edu/images

  33. Allotropes of Carbon Graphite Diamond Buckyballs

  34. Group 15: N, P, As, Sb, Bi White and red Phosphorus Ammonia,NH3

  35. Group 16: O, S, Se, Te, Po Shuttle main engines use H2 and O2 Sulfur

  36. Group 17: F, Cl, Br, I, At

  37. Group 18: He, Ne, Ar, Kr, Xe, Rn • Lighter than air balloons • “Neon” signs XeOF4

  38. Transition Elements Transition elements Inner transition elements lanthanides and actinides Iron in air gives iron(III) oxide

  39. Practice Problems • The formula for aluminum sulfide is Al2S3. What is the formula for gallium sulfide? Ga2S3 • What is the symbol and name of the element in period three and group fifteen? P phosphorus • What is the group and period for iodine? Period 5 and Group 17

  40. Summary of the Periodic Table Features 1. Name, Symbol, Atomic Number, Atomic Mass. 2. Solid, liquid, gas

  41. Summary of the Periodic Table Features 3. Divisions: metals vs. nonmetals groups(families) vs. periods(series) 1 alkali metals transition metals 2 alkaline earth metals inner transition metal (rare earth series) 17 halogens 18 noble gases (inert or rare gas) Main Group Elements (Representative Elements)

  42. Practice Problems 1. Draw atoms of O-16 and O-17. Determine A and Z for each. 2. An atom has 14 p+, 14 e-, and 17 n. Identify the element and write the complete symbol for this atom.

  43. Practice Problems Answers 1. O-16 Z = 8, A = 16 O-17 Z = 8, A = 17 Protons and neutrons in the nucleus. Electrons outside the nucleus. 2. 31 Si 14 3. a) In, Sr, Na, Ni b) P, At, S, Ar c) Ar d) Na e) At f) Ni g) none h) In, Sr, P, At, S, Na, Ar

  44. Practice Problems 4. Calculate the atomic weight of Mg from the following information: mass % abundance Mg-24 23.9850 amu 78.99% Mg-25 24.9858 amu 10.00% Mg-26 25.9825 amu 11.01%

  45. Practice Problems 5. Thallium metal, whose atomic mass is 204.384 amu, consists of two isotopes, Tl-203 and Tl-205. The isotopic mass of Tl-203 is 202.972 amu. and the isotopic mass of Tl-205 is 204.975 amu. a) Determine the number of protons, neutrons, and electrons in each isotope. b) What is the % abundance of each isotope?

  46. Practice Problems Answers 4. 24.31 amu 5. a) Tl-203 81 p, 81 e, 122 n Tl-205 81 p, 81 e, 124 n b) Tl-203 29.5% Tl-205 70.5%