Atoms molecules and ions chapter 2

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Atoms molecules and ions chapter 2

  1. 1. Chapter 2:Atoms, Molecules,and IonsChemistry 105
  2. 2. Atomic Theories of Matter Theories about the makeup of our world have been around for centuries: 5th Century BCE: 4th Century BCE: Chemistry 105 2
  3. 3. Atomic Theories 17th Century AD: 19th Century AD: Chemistry 105 3
  4. 4. Basis for Dalton’s theory Law of constant composition  Law of conservation of mass  Law of multiple proportions  Chemistry 105 4
  5. 5. Dalton’s Atomic Theory Dalton’s theory consists of 4 postulates: 1. Each element is composed of 2. All atoms of a given element are identical – but 3. Atoms of one element cannot 4. Compounds are formed when Chemistry 105 5
  6. 6. Late 19th century atomic theory In the 1850s, the discovery of cathode rays advanced the field of physics Chemistry 105 6
  7. 7. Discovery of the electron J.J. Thomson (1897)  Thomson observed that regardless of the material of the cathodes in the tube, Chemistry 105 7
  8. 8. Thomson’s Conclusions Based on the ways that the cathode rays interacted with electric and magnetic fields, he concluded that He concluded These particles would later be known as  Using experimental data, Thomson was able to successfully derive  Chemistry 105 8
  9. 9. Discovery of the electron Robert Millikan (1909)  Using X-rays as a _________________, Millikan shot ______ __________________ _________________ , suspending the droplets between charged plates to determine the charge of an electron Chemistry 105 9
  10. 10. Millikan’s conclusions  Therefore, the charge of an electron is  Using Thomson’s charge to mass ratio, Millikan concluded the mass of electron to be  Actual mass of electron: Chemistry 105 10
  11. 11. Radioactivity 1896 – Henri Bacquerel and his students, Pierre and Marie Curie, noted By 1910, the work of scientists like the Curies and Ernst Rutherford had Chemistry 105 11
  12. 12. Radioactivity Three types of radiation were discovered by Ernest Rutherford:    Chemistry 105 12
  13. 13. The gold foil experiment Rutherford shot a beam of ______________ at a small piece of foil, expecting __________ ____________________ ______, according to existing models of the atom Instead, Chemistry 105 13
  14. 14. Rutherford’s conclusions Since most of the alpha particles were He also concluded that since some of the particles were slightly deflected, Chemistry 105 14
  15. 15. Progression of the atomic model Chemistry 105 15
  16. 16. Other prominent discoveries 1919 – 1932 – Chemistry 105 16
  17. 17. Modern atomic theory Based on the experiments of the past,    Chemistry 105 17
  18. 18. Comparing the subatomic particles Protons and neutrons have Electrons, by contrast, Chemistry 105 18
  19. 19. Current atomic theory Based on the discoveries of the early 20th century and the development of quantum mechanics in the mid-20th century, the most current form of atomic theory is the quantum-mechanical model of the atom Chemistry 105 19
  20. 20. The quantum mechanical model Like the Rutherford model, Due to the nature of electrons, Instead, we think of electrons We can predict the most likely locations for these electrons  Chemistry 105 20
  21. 21. The Periodic Table 21 Scientists have been attempting to group and classify elements since the days of Aristotle However, the idea of an arrangement of the elements is a relatively new phenomenon Chemistry 105 21
  22. 22. Early periodic tables 1828 – Johann Wolfgang Döbereiner noticed trends where elements could be grouped together 1869 – Dmitri Mendeleev arranged the known elements by   Therefore,  were predicted in such a way 1914 – Henry Moseley Chemistry 105 22
  23. 23. Modern Periodic Table 23 Chemistry 105 23
  24. 24. Features of the periodic table Elements are arranged in a repeating, periodic pattern in order of atomic number The horizontal rows (7) of the periodic table are known as periods The vertical columns (18) of the periodic table are known as groups or families  Groups are numbered 1-18 (IUPAC) or IA-VIIIA and IB to VIIIB (Chemical Abstracts Service, CAS)  Common groups:      Chemistry 105 24
  25. 25. Regions of the Periodic Table The “staggered staircase”  The line that  Elements that appear on this line  Referred to as  Nonmetals  Metals   Special subgroups of metals   Chemistry 105 25
  26. 26. What does the table tell us? In addition to helping distinguish metal from nonmetal, the table actually gives us other important pieces of information Elemental symbol Atomic number (# of Name of protons in element nucleus) Atomic mass Chemistry 105 26
  27. 27. Other information 27 Protons and electrons   Neutrons  Chemistry 105 27
  28. 28. Isotopes 28 Atoms with Isotopes have Chemistry 105 28
  29. 29. Card Question #1 How many protons, neutrons, and electrons are in arsenic-75? A. 33 protons, 75 neutrons, 33 electrons B. 18 protons, 57 neutrons, 18 electrons C. 33 protons, 33 neutrons, 42 electrons D. 33 protons, 42 neutrons, 33 electrons Chemistry 105 29
  30. 30. Atomic mass The standard for atomic mass is the carbon-12 isotope  Defined as  1 mole of carbon-12 atoms All other atomic and molar masses are measured relative to the mass of the carbon-12 isotope Chemistry 105 30
  31. 31. Atomic weight Since multiple isotopes can exist for a given element, we take an average when discussing the atomic weight Example: carbon Atomic weight = Atomic weight = Chemistry 105 31
  32. 32. Card Question #2 Magnesium has three isotopes, Mg-24, Mg-25, and Mg-26. Using the data below, determine the average atomic mass for magnesium. Atomic mass Isotope Abundance (amu) Mg-24 78.99% 23.98504 Mg-25 10.00% 24.98584 Mg-26 11.01% 25.98259 A. 24.98 amu B. 24.31 amu C. 25.38 amu D. 28.71 amu Chemistry 105 32
  33. 33. Molecules With the exception of the noble gases, Several elements exist in nature in molecular form –  Examples:  Molecules made up of two atoms  Compounds composed of molecules that contain Chemistry 105 33
  34. 34. Molecular compounds Most molecular compounds consist of Chemical formulas:   Molecular formula   Empirical formula  Chemistry 105 34
  35. 35. Determining Empirical Formulas The empirical formula of a substance is often determined using a technique known as elemental analysis Elemental analysis is often performed using Chemistry 105
  36. 36. Elemental analysis by GC-MS As discussed before, GC is used to The mass spectrometer is able to determine Chemistry 105
  37. 37. Ions Recall that ions come in two forms: cations and anions  Cations are positively charged, anions are negatively charged How do ions become charged?    Charges typically ranges from for anions and . for cations Chemistry 105 37
  38. 38. Predicting ionic charges Atoms will gain or lose electrons to obtain the same number of electrons as Noble gas configurations are favored because We can then use the periodic table to  For each element moved toward the left,  For each element moved toward the right, Chemistry 105 38
  39. 39. Common charges Alkali metals have Alkaline earth metals have Chalogens have Halogens have Chemistry 105 39
  40. 40. Ionic compounds Ionic compounds are Ionic compounds are Ionic compounds must be  Chemistry 105 40
  41. 41. Writing Formulas Because compounds are electrically neutral, one can determine the formula of a compound this way:    Chemistry 105 41

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