2. New Way Chemistry for Hong Kong A-Level Book 11 Atomic Structure and Relative Masses 1.1The Atomic Nature of Matter 1.2The Experimental Evidence of Atomic Structure 1.3Sub-atomic Particles 1.4Atomic Number, Mass Number and Isotopes 1.5Mass Spectrometer 1.6Relative Isotopic, Atomic and Molecular Masses 1

3. New Way Chemistry for Hong Kong A-Level Book 12 1.1 The Atomic Nature of Matter

4. New Way Chemistry for Hong Kong A-Level Book 13 What is “atom”? 1.1 The atomic nature of matter (SB p.2) The Greek philosopher Democritus

5. New Way Chemistry for Hong Kong A-Level Book 14 Iron Continuous division 1.1 The atomic nature of matter (SB p.2) These are iron atoms!!

6. New Way Chemistry for Hong Kong A-Level Book 15 Dalton’s atomic theory John Dalton proposed his Dalton’s atomic theory 1.1 The atomic nature of matter (SB p.2)

7. New Way Chemistry for Hong Kong A-Level Book 16 Main points of Dalton’s atomic theory 1.1 The atomic nature of matter (SB p.2) 5.Atoms of different elements combine to form a compound. The numbers of various atoms combined bear a simple whole number ratio to each other. 1.All elements are made up of atoms. 2.Atoms can neither be created nor destroyed. 3.Atoms of the same element are identical. They have the same mass and chemical properties. 4.Atoms of different elements are different. They have different masses and chemical properties. Check Point 1-1 Check Point 1-1

8. New Way Chemistry for Hong Kong A-Level Book 17 The Experimental Evidence of Atomic Structure 1.2

9. New Way Chemistry for Hong Kong A-Level Book 18 1.2 The experimental evidence of atomic structure (SB p.3) Discovery of electrons A beam of rays came out from the cathode and hit the anode He called the beam cathode rays

10. New Way Chemistry for Hong Kong A-Level Book 19 1.2 The experimental evidence of atomic structure (SB p.4) The beam was composed of negatively charged fast-moving particles. Deflected in the electric field Deflected in the magnetic field

11. New Way Chemistry for Hong Kong A-Level Book 110 1.2 The experimental evidence of atomic structure (SB p.4) Measure the mass to charge ratio (m/e) of the particles produced Independent of the nature of the gas inside the discharge tube The particles were constituents of all atoms!! He called the particles ‘electrons’.

12. New Way Chemistry for Hong Kong A-Level Book 111 1.2 The experimental evidence of atomic structure (SB p.4) Thomson’s atomic model Atom An atom is electrically neutral No. of positively charged particles = No. of negatively charged particles

13. New Way Chemistry for Hong Kong A-Level Book 112 1.2 The experimental evidence of atomic structure (SB p.4) How are the particles distributed in an atom? + + + + + + Positive charge An atom was a positively charged sphere Negatively charged electrons embedded in it like a ‘raisin pudding’ Electron

14. New Way Chemistry for Hong Kong A-Level Book 113 1.2 The experimental evidence of atomic structure (SB p.4) Gold foil scattering experiment performed by Ernest Rutherford

15. New Way Chemistry for Hong Kong A-Level Book 114 1.2 The experimental evidence of atomic structure (SB p.4) He bombarded a thin gold foil with a beam of fast-moving  -particles (+ve charged) Observation: most  -particles passed through the foil without deflection very few  -particles were scattered or rebounded back

16. New Way Chemistry for Hong Kong A-Level Book 115 1.2 The experimental evidence of atomic structure (SB p.5) Interpretation of the experimental results The condensed core is called ‘nucleus’ The positively charged particle is called ‘proton’

17. New Way Chemistry for Hong Kong A-Level Book 116 1.2 The experimental evidence of atomic structure (SB p.5) Rutherford’s atomic model Expectation: Mass of atom = Total mass of protons Mass of atom > Total mass of protons

18. New Way Chemistry for Hong Kong A-Level Book 117 1.2 The experimental evidence of atomic structure (SB p.5) Chadwick’s atomic model presence of neutrons proved by James Chadwick

19. New Way Chemistry for Hong Kong A-Level Book 118 Chadwick’s atomic model 1.2 The experimental evidence of atomic structure (SB p.5) Proton Electron Neutron Check Point 1-2 Check Point 1-2

20. New Way Chemistry for Hong Kong A-Level Book 119 Sub-atomic Particles 1.3

21. New Way Chemistry for Hong Kong A-Level Book 120 Sub-atomic particles 1.3 Sub-atomic particles (SB p.6) 3 kinds of sub-atomic particles: Protons Neutrons Electrons Inside the condensed nucleus Moving around the nucleus

22. New Way Chemistry for Hong Kong A-Level Book 121 A carbon-12 atom 1.3 Sub-atomic particles (SB p.7)

23. New Way Chemistry for Hong Kong A-Level Book 122 Characteristics of sub-atomic particles 1.3 Sub-atomic particles (SB p.6) Sub-atomic particle ProtonNeutronElectron Symbolp orn ore - or Location in atom Nucleus Surrounding the nucleus Actual charge (C) 1.6  10 -9 01.6 x 10 -9 Relative charge+10 Actual mass (g) 1.7  10 -24 9.1  10 -28 Approximate relative mass (a.m.u.) 110 H 1 1 n 1 0 e 0

24. New Way Chemistry for Hong Kong A-Level Book 123 Relative size of the atom and the nucleus 1.3 Sub-atomic particles (SB p.6) Check Point 1-3 Check Point 1-3

25. New Way Chemistry for Hong Kong A-Level Book 124 Atomic Number, Mass Number and Isotopes 1.4

26. New Way Chemistry for Hong Kong A-Level Book 125 Atomic number 1.4 Atomic number, mass number and isotopes (SB p.7) The atomic number (Z) of an element is the number of protons contained in the nucleus of the atom. Atomic number = Number of protons Number of electrons = Reason: Atoms are electrically neutral. WHY ?

27. New Way Chemistry for Hong Kong A-Level Book 126 Mass number 1.4 Atomic number, mass number and isotopes (SB p.8) The mass number (A) of an atom is the sum of the number of protons and neutrons in the nucleus. Mass number = Number of protons Number of neutrons +

28. New Way Chemistry for Hong Kong A-Level Book 127 Atomic numbers and mass numbers of some common atoms 1.4 Atomic number, mass number and isotopes (SB p.8) AtomNo. of protons No. of electrons No. of neutrons Atomic number Mass number Hydrogen1101(1 + 0) = 1 Oxygen8888(8 + 8) = 16 Argon18 2218(18+22) = 40

29. New Way Chemistry for Hong Kong A-Level Book 128 Isotopes 1.4 Atomic number, mass number and isotopes (SB p.8) Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. Representation: X A Z Symbol of the element Mass number Atomic number

30. New Way Chemistry for Hong Kong A-Level Book 129 1.4 Atomic number, mass number and isotopes (SB p.8) e.g. the two isotopes of chlorine are written as: Cl 35 17 Cl 37 17 OR labelled as Cl-35 and Cl-37. Check Point 1-4 Check Point 1-4

31. New Way Chemistry for Hong Kong A-Level Book 130 1.4 Atomic number, mass number and isotopes (SB p.9) ElementIsotopeAtomic number No. of protons No. of neutrons Natural abundanc e (%) Hydrogen11099.8 1110.02 Carbon66698.89 6671.11 668trace Isotopes of some common elements H 1 1 H 2 1 C 12 6 C 13 6 C 14 6

32. New Way Chemistry for Hong Kong A-Level Book 131 Mass Spectrometer 1.5

33. New Way Chemistry for Hong Kong A-Level Book 132 1.5 Mass spectrometer (SB p.10) Mass spectrometer A highly accurate instrument!

34. New Way Chemistry for Hong Kong A-Level Book 133 Mass spectrometer consists of 6 parts: 1.5 Mass spectrometer (SB p.10)

35. New Way Chemistry for Hong Kong A-Level Book 134 Mass spectrum of Cl 2 : 1.8 Mass spectrometer (SB p.21) m/e ratioCorresponding ion 35 35 Cl + 37 37 Cl + 70 35 Cl─ 35 Cl + 72 35 Cl ─ 37 Cl + 74 37 Cl ─ 37 Cl +

36. New Way Chemistry for Hong Kong A-Level Book 135 Mass spectrum of CH 3 Cl: m/e ratioCorresponding ion 35 35 Cl + 37 37 Cl + 50 12 CH 3 ─ 35 Cl + 51 13 CH 3 ─ 37 Cl + 52 12 CH 3 ─ 37 Cl + 1.8 Mass spectrometer (SB p.21) Check Point 1-5 Check Point 1-5

37. New Way Chemistry for Hong Kong A-Level Book 136 Relative Isotopic, Atomic and Molecular Masses 1.6

38. New Way Chemistry for Hong Kong A-Level Book 137 1.9 Relative isotopic, atomic and molecular masses (SB p.22) Relative isotopic mass The relative isotopic mass of a particular isotope of an element is the relative mass of one atom of that isotope on the carbon-12 scale. e.g.relative isotopic mass of Cl-35 = 35 relative isotopic mass of Cl-37 = 37

39. New Way Chemistry for Hong Kong A-Level Book 138 1.9 Relative isotopic, atomic and molecular masses (SB p.22) What is carbon-12 scale? Mg has the same mass as two C-12 atoms use carbon-12 as the reference standard

40. New Way Chemistry for Hong Kong A-Level Book 139 Relative atomic mass The relative atomic mass of an element is the weighted average of the relative isotopic masses of its natural isotopes on the carbon-12 scale. 1.9 Relative isotopic, atomic and molecular masses (SB p.23)

41. New Way Chemistry for Hong Kong A-Level Book 140 1.9 Relative isotopic, atomic and molecular masses (SB p.23) What is the relative atomic mass of Cl? The relative abundances of Cl-35 and Cl-37 are 75.77 and 24.23 respectively Relative atomic mass of Cl = = 35.48

42. New Way Chemistry for Hong Kong A-Level Book 141 Relative molecular mass 1.9 Relative isotopic, atomic and molecular masses (SB p.23) The relative molecular mass is the relative mass of a molecule on the carbon-12 scale.

43. New Way Chemistry for Hong Kong A-Level Book 142 1.9 Relative isotopic, atomic and molecular masses (SB p.23) What is the relative molecular mass of CH 3 Cl? Relative molecular mass of CH 3 Cl = = 50.50 Example 1-6 Example 1-6 Check Point 1-6 Check Point 1-6

44. New Way Chemistry for Hong Kong A-Level Book 143 The END

45. New Way Chemistry for Hong Kong A-Level Book 144 (a)What does the word “atom” literally mean? (b)Which point of Dalton’s atomic theory is based on the law of conservation of mass proposed by Lavoisier in 1774 which states that matter is neither created nor destroyed in the course of a chemical reaction? (c)Which point of Dalton’s atomic theory is based on the law of constant proportion proposed by Proust in 1799 which states that all pure samples of the same chemical compound contain the same elements combined together in the same proportions by mass? 1.1 The atomic nature of matter (SB p.3) (a) Indivisible (b) Atoms can neither be created nor destroyed. (c) Atoms of different elements combine to form a compound. The numbers of various atoms combined bear a simple whole number ratio to each other. Back Answer

46. New Way Chemistry for Hong Kong A-Level Book 145 (a)Atoms were found to be divisible. What names wer given to the particles found inside the atoms? (b)Give the most important point of the following experiments: (i)E. Goldstein’s gas discharge tube experiment; (ii)J. J. Thomson’s cathode ray tube experiment; (iii) E. Rutherford’s gold foil scattering experiment. 1.2 The Experimental evidence of atomic structure (SB p.4) (a) Electron, proton and neutron (b) (i) Discovery of cathode rays (ii) Discovery of electrons (iii) Discovery of nucleus in atoms Back Answer

47. New Way Chemistry for Hong Kong A-Level Book 146 The identity of an element is determined by the number of which sub-atomic particle? Back 1.3 Sub-atomic particles (SB p.6) The identity of an element is determined by the number of protons in its atomic nucleus. Answer

48. New Way Chemistry for Hong Kong A-Level Book 147 (a)Which part of the atom accounts for almost all the mass of that atom? (b)The mass of which sub-atomic particle is often assumed to be zero? 1.3 Sub-atomic Particles (SB p.7) (a) Nucleus (b) Electron Back Answer

49. New Way Chemistry for Hong Kong A-Level Book 148 Are there any sub-atomic particles other than protons, neutrons and electrons? Back 1.3 Sub-atomic particles (SB p.7) Other than the three common types of sub- atomic particles (proton, neutron and electron), there are also some sub-atomic particles called positron (anti-electron) and quark. Answer

50. New Way Chemistry for Hong Kong A-Level Book 149 If bromine has two isotopes, 79 Br and 81 Br, how many physically distinguishable combinations of Br atoms are there in Br 2 ? Back 1.3 Sub-atomic particles (SB p.7) There are three physically distinguishable combinations of Br atoms ( 79 Br— 79 Br, 79 Br— 81 Br and 81 Br— 81 Br) in Br 2. Answer

51. New Way Chemistry for Hong Kong A-Level Book 150 Write the symbol for the atom that has an atomic number of 11 and a mass number of 23. How many protons, neutrons and electrons does this atom have? 1.4 Atomic number, mass number and isotopes (SB p.8) Back, 11 protons, 12 neutrons, 11 electrons. Answer

52. New Way Chemistry for Hong Kong A-Level Book 151 Label the different parts of the mass spectrometer. 1.5 Mass spectrometer (SB p.12) Back A – Vaporization chamber B – Ionization chamber C – Accelerating electric field D – Deflecting magnetic field E – Ion detector Answer

53. New Way Chemistry for Hong Kong A-Level Book 152 The mass spectrum of neon is given below. Determine the relative atomic mass of neon. 1.5 Mass spectrometer (SB p.12) Back Relative atomic mass of neon = = 20.18 Answer

54. New Way Chemistry for Hong Kong A-Level Book 153 (a) The mass spectrum of lead is given below. Given that the relative atomic mass of lead is 207.242, calculate the relative abundance of the peak at m/e of 208. 1.6 Relative isotopic, atomic and molecular masses (SB p.14) Let x be the relative abundance of the peak at m/e of 208. (204  1.5 + 206  23.6 + 207  22.6 + 208x)  (1.5 + 23.6 + 22.6 + x) = 207.242 x = 52.3 The relative abundance of the peak at m/e of 208 is 52.3. Answer

55. New Way Chemistry for Hong Kong A-Level Book 154 (b) The mass spectrum of dichloromethane is given below. Calculate the relative molecular mass of dichloromethane. Back 1.6 Relative isotopic, atomic and molecular masses (SB p.14) The relative molecular mass of dichloromethane = (84  94 + 85  3.0 + 86  59 + 87  2.2 + 88  13 + 89  2.5 + 90  0.8)  (94 + 3.0 + 59 + 2.2 + 13 + 2.5 + 0.8) = 85.128 The relative molecular mass of dichloromethane is 85.128. Answer