1. 1.2 Atomic Structure (Time needed: 6 class periods)

2. Learning outcomes
Matter is composed of particles, which may be atoms, molecules or ions.
Atoms. Minute size of atoms.
Law of conservation of mass.

3. DIFFUSION- evidence for the existence of small particles
SPREADING OUT OF GASES
COLOUR OF INK SREADING OUT WHEN MIXED WITH WATER
HYDROGEN CHLORIDE AND AMMONIA SOLUTION

4. AMMONIUM CHLORIDE

5. law of conservation of mass/matter
The law of conservation of mass/matter, also known as law of mass/matter conservation says that the mass of a closed system will remain constant, regardless of the processes acting inside the system.
Matter cannot be created/destroyed, although it may be rearranged.
For any chemical process in a closed system, the mass of the reactants must equal the mass of the products.

8. Learning Outcomes
Very brief outline of the historical development of atomic theory (outline principles only; mathematical treatment not required): Dalton: atomic theory;
Crookes: vacuum tubes, cathode rays;
Stoney: naming of the electron;
Thomson: negative charge of the electron; e/m for electrons (experimental details not required);
Millikan: magnitude of charge of electrons as shown by oil drop experiment (experimental details not required);
Rutherford: discovery of the nucleus as shown by the α−particle scattering experiment;
discovery of protons in nuclei of various atoms;
Bohr: model of the atom;
Chadwick: discovery of the neutron.

9. HISTORY OF THE ATOM
GREEKS – MATTER MADE OF TINY INDIVISIBLE PARTICLES

10. DALTON 1766-1844 ALL MATTER MADE OF SMALL PARTICLES CALLED ATOMS
ATOMS ARE INDIVISIBLE
ATOMS CANNOT BE CREATED OR DESTROYED

11. DISCOVERY OF THE ELECTRON
CROOKES CONDUCTED EXPERIMENTS WITH A GLASS TUBE

12. CROOKES TUBE

13. CROOKES TUBES CATHODE CONNECTED TO NEGATIVE ELECTRODE
ANODE CONNECTED TO THE POSITIVE ELECTRODE
CNAP

14. VACUUM TUBES GAS AT LOW PRESSURE ELECTRIC CURRENT PASSED THROUGH
RADIATION CAME FROM THE END OF THE TUBE CONNECTED TO THE NEGATIVE(CATHODE) END OF THE BATTERY
CATHODE RAYS

15. TUBES

16. CROOKES PADDLE TUBE

17. CATHODE RAYS CAST SHADOWS CAUSE GLASS TO GLOW TURN A PADDLE WHEEL
RAYS ARE MADE OF PARTICLES

18. JJ THOMPSON HOLE IN ANODE TO ALLOW BEAM OF RAYS TO PASS THROUGH.
BEAM COULD BE DEFLECTED BY ELECTRIC PLATES.
THEREFORE BEAM IS MADE OF NEGATIVE PARTICLES.

19. JJ THOMPSONS APPARATUS

20. JJ THOMPSON
USED A MAGNETIC FIELD FROM AN ELECTROMAGNET TO DEFLECT THE ELECTRONS
CALCULATED THE RATIO OF CHARGE TO MASS FOR ELECTRON

21. GEORGE STONEY
NAMED PARTICLES ELECTRONS

22. ROBERT MILLIKAN FAMOUS OIL-DROP EXPERIMENT
IT MEASURED THE CHARGE ON THE ELECTRON
X-RAYS IONISED AIR MOLECULES BY STRIPING ELECTRONS OFF THEIR ATOMS.
OIL DROPLETS PICKED UP ELECTRONS BECAME NEGATIVE
INCREASED THE + CHARGE UNTIL THE DROPLET HOVERED.
TOOK MEASUREMENTS AND CALCULATED THE CHARGE ON THE ELECTRON.

23. ROBERT MILLIKAN

24. ROBERT MILLIKAN

25. THOMPSON’S ATOM
ATOM A SPHERE OF POSITIVE CHARGES WITH NEGATIVE ELECTONS EMBEDDED

26. ERNEST RUTHERFORD FIRED THIN ALPHA PARTICLES AT A TIN GOLD FOIL
THOMPSONS PLUM PUDDING MODEL PREDICTED THAT THEY WOULD PASS THRU’ WITH LITTLE DEFLECTION

27. RUTHERFORD’S EXPT

28. RUTHERFORD’S EXPT

29. EXPECTED RESULT
ALPHA PARTICLES SHOULD PASS THROUGH WITH LITTLE DEFLECTION +
+ +

30. ACTUAL RESULT
MOST PASS THROUGH UNDEFLECTED
SOME BOUNCED RIGHT BACK!

31. EXPLANATION
HARD DENSE CORE OF POSITIVE MATTER IN THE CENTER OF EACH ATOM-NUCLEUS
ATOMS ARE MOSTLY EMPTY SPACE.

32. THE PROTON
RUTHERFORD CONTINUED TO BOMBARD DIFFERENT ELEMENTS SUCH AS NITROGEN AND OXYGEN
SMALL POSITIVE PARTICLES WERE GIVEN OFF--- PROTONS

33. THE NEUTRON JAMES CHADWICK BOMBARDED BERYLLIUM WITH ALPHA PARTICLES.
SMALL PARTICLES WERE GIVEN OFF WHICH WERE NEUTRAL AND HAD THE SAME MASS AS THE PROTON—THE NEUTRON.

35. Electrons travel in orbits around the nucleus
Bohr’s atom
Electrons travel in orbits around the nucleus

37. Learning Outcomes
Properties of electrons, protons and neutrons (relative mass, relative charge, location within atom).

38. Proton
Protons are positively charged particles found within atomic nucleus

41. Learning Outcomes
Atomic number (Z ), mass number (A), isotopes; hydrogen and carbon as examples of isotopes.
Relative atomic mass (A r). The
12C scale for relative atomic
masses.

42. Atomic number
Also called proton number, this is the number of protons the atom has

45. Atomic number
Also called proton number, this is the number of protons the atom has

46. The Number of Electrons
Atoms must have equal numbers of protons and electrons. In our example, an atom of krypton must contain 36 electrons since it contains 36 protons.

47. Mass Number = (Number of Protons) + (Number of Neutrons)

48. Isotope
Atoms that have the same number of protons but different numbers of neutrons are called isotopes

50. Hydrogen isotopes
The element hydrogen for example, has three commonly known isotopes: protium, deuterium and tritium

51. Deuterium
an atom of deuterium consists of one proton one neutron and one electron

52. Tritium
An atom of tritium consists of one proton two neutrons and one electrons

54. Relative Atomic Mass
The relative atomic mass of an element the mass of one of the element's atoms -- relative to the mass of an atom of Carbon 12,

55. Learning Outcomes
Calculation of approximate relative atomic masses from abundance of isotopes of given mass number (e.g. Calculation of approximate relative atomic mass of chlorine).

56. Chlorine-35 and Chlorine-37 are both isotopes of chlorine

57. Relative mass of chlorine
Chlorine consists of roughly 75% Chlorine-35 and roughly 25% Chlorine-37. We take an average of the two figures The relative atomic mass of chlorine is usually quoted as 35.5.

59. Learning outcomes
Use of the mass spectrometer in determining relative atomic mass.
Fundamental processes that occur in a mass spectrometer:
vaporisation of substance,
production of positive ions,
acceleration, separation,
detection (mathematical
treatment excluded).

60. THE MASS SPECTROMETER
Atoms can be deflected by magnetic fields - provided the atom is first turned into an ion.

61. Stage 1: Ionisation
The atom is ionised by knocking one or more electrons off to give a positive ion.

62. Stage 2: Acceleration
The ions are accelerated so that they all have the same kinetic energy.

63. Stage 3: Deflection
The ions are then deflected by a magnetic field according to their masses. The lighter they are, the more they are deflected.

64. The beam of ions passing through the machine is detected electrically.
Stage 4: Detection
The beam of ions passing through the machine is detected electrically.