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Chapter 2

Chapter 2. Atoms and Elements. Dalton’s Atomic Theory. Postulates proposed in 1803 know for first exam. Dalton’s Atomic Theory. Postulate 1 An element is composed of tiny particles called atoms. All atoms of a given element show the same chemical properties.

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Chapter 2

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  1. Chapter 2 Atoms and Elements Dr. S. M. Condren

  2. Dalton’s Atomic Theory Postulates • proposed in 1803 • know for first exam Dr. S. M. Condren

  3. Dalton’s Atomic Theory Postulate 1 • An element is composed of tiny particles called atoms. • All atoms of a given element show the same chemical properties. Dr. S. M. Condren

  4. Atoms of different elements have different properties. Dalton’s Atomic Theory Postulate 2 Dr. S. M. Condren

  5. Dalton’s Atomic Theory Postulate 3 • Compounds are formed when atoms of two or more elements combine. • In a given compound, the relative number of atoms of each kind are definite and constant. Dr. S. M. Condren

  6. Dalton’s Atomic Theory Postulate 4 • In an ordinary chemical reaction, no atom of any element disappears or is changed into an atom of another element. • Chemical reactions involve changing the way in which the atoms are joined together. Dr. S. M. Condren

  7. Composed of: protons neutrons electrons protons found in nucleus relative charge of +1 relative mass of 1.0073 amu Structure of the Atom Dr. S. M. Condren

  8. Composed of: protons neutrons electrons neutrons found in nucleus neutral charge relative mass of 1.0087 amu Structure of the Atom Dr. S. M. Condren

  9. Composed of: protons neutrons electrons electrons found in electron cloud relative charge of -1 relative mass of 0.00055 amu Structure of the Atom Dr. S. M. Condren

  10. ATOM COMPOSITION The atom is mostly empty space • protons and neutrons in the nucleus. • the number of electrons is equal to the number of protons in a neutral atom. • electrons in space around the nucleus. • extremely small. One teaspoon of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of water. Dr. S. M. Condren

  11. Radioactivity • Alpha – helium-4 nucleus • Ra226 Rn222 + He4(a) • Beta – high energy electron • U239 Np239 + b-1 • Gamma – energy resulting from transitions from one nuclear energy level to another • Ni60* Ni60 + g Dr. S. M. Condren

  12. Penetrations ofRadioactive Emissions Dr. S. M. Condren

  13. Isotopes & Their Uses Heart scans with radioactive technetium-99. 9943Tc Emits gamma rays Dr. S. M. Condren

  14. The modern view of the atom was developed by Ernest Rutherford(1871-1937). Dr. S. M. Condren

  15. Rutherford’s Model of the Atom • atom is composed mainly of vacant space • all the positive charge and most of the mass is in a small area called the nucleus • electrons are in the electron cloud surrounding the nucleus Dr. S. M. Condren

  16. Nucleus If nucleus is 1” The atom would be 1.5 miles in diameter Dr. S. M. Condren

  17. Ions • Ion • electrostatically charged atom or group of atoms • cations • positive ions • anions • negative ions • ionic compounds • combination of cations and anions • zero net charge Dr. S. M. Condren

  18. Atomic number Atom symbol Atomic weight Atomic number, Z • the number of protons in the nucleus • the number of electrons in a neutral atom • the integer on the periodic table for each element 13 Al 26.981 Dr. S. M. Condren

  19. Dr. S. M. Condren

  20. Imaging Dr. S. M. Condren

  21. Which best represents the poles? Dr. S. M. Condren

  22. Quantum Corral http://www.almaden.ibm.com/vis/stm/corral.html Dr. S. M. Condren

  23. Mass Number,A • C atom with 6 protons and 6 neutrons is the mass standard • = 12 atomic mass units (u) • Mass Number (A) = # protons + # neutrons • A boron atom can have A = 5 p + 5 n = 10 u Dr. S. M. Condren

  24. Isotopes • atoms of the same element which differ in the number of neutrons in the nucleus • designated by mass number Dr. S. M. Condren

  25. Isotopes of Hydrogen H-1, 1H, protium • 1 proton and no neutrons in nucleus • only isotope of any element containing no neutrons in the nucleus • most common isotope of hydrogen Dr. S. M. Condren

  26. Isotopes of Hydrogen H-2 or D, 2H, deuterium • 1 proton and 1 neutron in nucleus Dr. S. M. Condren

  27. Isotopes of Hydrogen H-3 or T, 3H, tritium • 1 proton and 2 neutrons in nucleus radioactive electron antineutrino Dr. S. M. Condren

  28. The radioactive isotope 14C has how many neutrons? 6, 8, other Dr. S. M. Condren

  29. The identity of an element is determined by the number of which particle? protons, neutrons, electrons Dr. S. M. Condren

  30. Mass Spectrometer a simulation is available at http://www.colby.edu/chemistry/OChem/DEMOS/MassSpec.html Dr. S. M. Condren

  31. Mass spectrum of C6H5Br Dr. S. M. Condren

  32. Atomic Masses andIsotopic Abundances natural atomic masses = SUM[(atomic mass of isotope) *(fractional isotopic abundance)] Dr. S. M. Condren

  33. Example: Chlorine has two isotopes, Cl-35 and Cl-37, which have masses of 34.96885 and 36.96590 amu, respectively. The natural atomic mass of chlorine is 35.453 amu. What are the percent abundances of the two isotopes? let x = fraction Cl-35 y = fraction Cl-37 x + y = 1 y = 1 - x (AW Cl-35)(fraction Cl-35) + (AW Cl-37)(fraction Cl-37) = 35.453 Thus: 34.96885*x + 36.96590*y = 35.453 34.96885*x + 36.96590*(1-x) = 35.453 Thus 24.243% Cl-37 x = 0.75757 <=> 75.757% Cl-35 Dr. S. M. Condren

  34. Molar Mass-Molecular Weight Sum atomic masses represented by formula atomic masses => gaw molar mass => MM Dr. S. M. Condren

  35. Example What is the molar mass of ethanol, C2H5O1H1? MM = 2(gaw)C + (5 + 1)(gaw)H + 1(gaw)O = 2(12.011)C + 6(1.00794)H + 1(15.9994)O = 24.022 + 6.04764 + 15.9994 = 46.069 g/mol Significant figures rule for multiplication Significant figures rule for addition Sequence – multiplication then addition, apply significant figure rules in proper sequence Dr. S. M. Condren

  36. The Mole • a unit of measurement, quantity of matter present • Avogadro’s Number 6.022 x 1023 particles • Latin for “pile” Dr. S. M. Condren

  37. One Mole of each Substance Clockwise from top left: 1-Octanol, C8H17OH; Mercury(II) iodide, HgI2; Methanol, CH3OH; and Sulfur, S8. Dr. S. M. Condren

  38. Example How many moles of carbon dioxide molecules are there in 10.00g of carbon dioxide? MM = 1(gaw)C + 2(gaw)O = 44.01 g/mol / / #mol CO2 (1 mol/44.01g) = (10.00g) = 0.2272 mol Dr. S. M. Condren

  39. Mendeleev’s Periodic Table Missing elements: 44, 68, 72, & 100 amu Dr. S. M. Condren

  40. Properties of Ekasilicon Dr. S. M. Condren

  41. Modern Periodic Table the elements are arranged according to increasing atomic numbers Dr. S. M. Condren

  42. Periodic Table of the Elements Dr. S. M. Condren

  43. Organization of Periodic Table • period - horizontal row • group - vertical column Family Names • Group IA alkali metals • Group IIA alkaline earth metals • Group VIIA halogens • Group VIIIA noble gases • transition metals • inner transition metals • lanthanum series rare earths • actinium series trans-uranium series Dr. S. M. Condren

  44. Dr. S. M. Condren

  45. ELEMENTS THAT EXIST AS MOLECULES Allotropes of C Dr. S. M. Condren

  46. Dr. S. M. Condren

  47. ELEMENTS THAT EXIST AS DIATOMIC MOLECULES Dr. S. M. Condren

  48. ELEMENTS THAT EXIST AS POLYATOMIC MOLECULES S8 sulfur molecules White P4 and polymeric red phosphorus Dr. S. M. Condren

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