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Unit Objectives

Unit Objectives. 1)understand the evolution of models of the atom: Dalton, Thomson, Rutherford, Bohr, the ‘quantum model 2 ) understand the meaning of mass number, atomic (proton) number. 3) be able to write and work with full atomic symbols

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Unit Objectives

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  1. Unit Objectives 1)understand the evolution of models of the atom: Dalton, Thomson, Rutherford, Bohr, the ‘quantum model 2) understand the meaning of mass number, atomic (proton) number. 3) be able to write and work with full atomic symbols 4) be able to calculate relative atomic, molecular and formula mass

  2. Refreshing some Old Terminology • Bohr Rutherford Diagrams • Isotopes and ions • R.A.M. (Relative Atomic Mass)

  3. What is “atom”? The Greek philosopher Democritus

  4. Continuous division Continuous division These are iron atoms!! Iron

  5. Main points of Dalton’s atomic theory Dalton’s atomic theory 1. All elements are made up of atoms. 2. Atoms are not created or destroyed. • Atoms of the same element have the same mass and chemical properties. 4. Atoms of different elements are different. They have different masses and chemical properties. 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.

  6. JJ Thompson Raisin Pudding Model Discovery of electrons • A beam of rays came out from the cathode and hit the anode. • He called the beam cathode rays.

  7. Deflected in the electric field Deflected in the magnetic field The beam was composed of negatively charged fast-moving particles.

  8. + + + + + + Electron Positive charge Thompson’s Raisin Bun Model How are the particles distributed in an atom? • An atom was a positively charged sphere - Negatively charged electrons embedded in it like a ‘raisin pudding’

  9. Gold foil scattering experiment - performed by Ernest Rutherford

  10. 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

  11. Interpretation of the experimental results - The condensed core is called ‘nucleus’. - The positively charged particle is called ‘proton’.

  12. Proton Electron Neutron Chadwick’s atomic model Provedthe presence of neutrons

  13. Interpret the diagram • Protons are deflected on a curved path towards the negative plate. • Electrons are deflected on a curved path towards the positive plate. The amount of deflection is exactly the same in the electron beam as the proton beam if the energies are the same - but, of course, it is in the opposite direction. • Neutrons continue in a straight line.

  14. Practice Fill in the Chart

  15. MASS NUMBER AND ATOMIC NUMBER

  16. Review of Models of the Atom(7 min) https://www.youtube.com/watch?v=kBgIMRV895w

  17. Bohr's Model of the Atom Niels Bohr (1913): -studied the light produced when atoms was excited by heat or electricity

  18. Bohr's Model of the Atom Niels Bohr (1913): -studied the light produced when atoms were excited by heat or electricity Rutherford's model couldn't explain why unique colours were obtained by atoms of different elements Bohr proposed that electrons are in orbits & when excited jump to a higher orbit. When they fall back to the original they give off light

  19. Bohr's Model of the Atom Bohr's model: -electrons orbit the nucleus like planets orbit the sun -each orbit can hold a specific maximum number of electrons

  20. Atomic Model Development

  21. 0 e -1 1 1 H n 1 0 Characteristics of sub-atomic particles

  22. Atomic number Number of protons Number of electrons = = Reason:Atoms are electrically neutral. Atomic number The atomic number (Z) of an element is the number of protons contained in the nucleus of the atom. WHY?

  23. Mass number Number of protons Number of neutrons = + Mass number The mass number (A) of an atom is the sum of the number of protons and neutrons in the nucleus.

  24. Atomic numbers and mass numbers

  25. Representation: Symbol of the element Mass number A X Z Atomic number Isotopes Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.

  26. 35 37 Cl Cl 17 17 e.g. the two isotopes of chlorine are written as: OR labelled asCl-35andCl-37.

  27. 23 Na 11 MASS NUMBER AND ATOMIC NUMBER Atomic Number (Z) Number of protons in the nucleus of an atom Mass Number (A) Sum of the protons and neutrons in the nucleus Mass Number (A) PROTONS + NEUTRONS Atomic Number (Z) PROTONS

  28. Fuse SchoolIsotopes https://www.youtube.com/watch?v=o7Kpk3al_uo

  29. The Configuration of Electrons

  30. Bohr-Rutherford Energy Diagrams Ideas about the structure of the atom have changed over the years. The Bohr theory thought of it as a small nucleus of protons and neutrons surrounded by circulating electrons. Each shell or energy level could hold a maximum number of electrons. The energy of levels became greater as they got further from the nucleus and electrons filled energy levels in order. Maximum electrons per shell 1st shell 2 2nd shell 8 3rd shell 18 4th shell 32 5th shell 50

  31. The arrangement of the electrons The electrons are found in ENERGY LEVELS The first level will only hold 2 electrons, the second holds 8, and the third also 8 electrons. These levels can be thought of as getting progressively further from the nucleus.

  32. What is the electronic arrangement in chlorine ? Atomic number = 17. Therefore there are 17 protons and 17 electrons. The arrangement of the electrons will be 2, 8, 7 (i.e. 2 in the first level, 8 in the second, and 7 in the third). The electronic arrangements of the first 20 elements

  33. Practice Handout Please do the handout on energy level diagrams

  34. ISOTOPES &AVERAGE ATOMIC OR MOLAR MASS

  35. 90.92 Abundance / % 8.82 0.26 19 20 21 22 23 m/z MASS SPECTRA R.A.M. Consider neon and its 3 isotopes... 20Ne21Ne22Ne. We use these values to determine the average molar mass of an element or Relative atomic mass, called RAM Calculate the average relative atomic mass of neon using the above information. Out of every 100 atoms 90.92 are 20Ne , 0.26 are 21Ne and 8.82 are 22Ne Average = (90.92 x 20) + (0.26 x 21) + (8.82 x 22) = 20.179 100 Relative atomic mass = 20.18

  36. Calculate the relative atomic mass of the following – give your answers to 3 significant figures Bromine : 79 Br 50% , 81 Br 50% Copper : 63 Cu 69% , 65 Cu 31% Zirconium : 90 Zr 51.5% , 91 Zr 11.2%, 92 Zr 17.1%, 94 Zr 17.4%, 96 Zr 2.8% Lead : 204 Pb 1.5% , 206 Pb 23.6%, 207 Pb 22.6%, 208 Pb 52.3% Neon : 20 Ne 90.9% , 21 Ne 0.2%, 22 Ne 8.9% 63.6 91.3 207. 20.2

  37. Can we calculate the % composition if we know the isotopes ? Naturally occurring potassium consists of potassium-39 and potassium-41. Calculate the percentage of each isotope present if the average is 39.1. Assume there are x nuclei of 39K in every 100; so there will be (100-x) of 41K so 39x + 41 (100-x) = 39.1 100 therefore 39 x + 4100 - 41x = 3910 thus - 2x = - 190 and x = 95 ANSWER There will be95%39K and 5% 41K

  38. Right, ok now you try, see the handout

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