The Structure of Matter

1. The Structure of Matter

2. PIONEERS OF THE ATOM DEMOCRITUS LAVOISIER DALTON THOMPSON MILLIKEN RUTHERFORD BOHR

3. THE EARLY ATOM It’s all Greek to me …… DEMOCRITUS IS THE MAN !

4. DEMOCRITUS WAS A GREEK PHILOSOPHER THAT BEGAN WONDERING WHAT WAS THE UNIVERSE MADE OF. HE PROPOSED THAT ALL THE MATTER IN THE UNIVERSE IS COMPOSED OF ‘TINY PARTICLES’. THESE PARTICLES ARE ‘INDIVISIBLE’. HE CALLED THESE PARTICLES ‘ATOMOS’ (MEANING ‘INDIVISIBLE’). BUT HE HAD AN OPPONENT……

5. ARISTOTLE = SKEPTIC Democritus is an ignoramus! ARISTOTLE WAS MUCH MORE POPULAR AND HE OPPOSED THE IDEA OF ‘ATOMS’

6. ARISTOTLE = SKEPTIC Democritus is an ignoramus! ARISTOTLE BELIEVED THAT MATTER WAS ‘CONTINUOUS’.

7. ARISTOTLE’S FOUR BASIC ELEMENTSEARTH, AIR, FIRE and WATER

8. BECAUSE OF ARISTOTLE’S GREAT INFLUENCE…… DEMOCRITUS’ ATOMS

9. ...’ATOMS’ DIED FOR ABOUT 1,400 YEARS UNTIL...

10. IN THE 1700’S…

11. THE PREDOMINATE BELIEF BY THE MID 1700’S WAS THE MODERN DEFINITION OF AN ELEMENT AS A SUBSTANCE THAT CANNOT BE BROKEN DOWN BY ORDINARY CHEMICAL MEANS. IT WAS ALSO BELIEVED THAT ELEMENTS COMBINE TO FORM COMPOUNDS THAT HAVE DIFFERENT PHYSICAL AND CHEMICAL PROPERTIES THAN THOSE OF THE ELEMENTS THAT FORM THEM.

12. HOWEVER, THERE WAS CONTROVERSY AS TO WHETHER ELEMENTS ALWAYS COMBINE IN THE SAME RATIO WHEN FORMING A PARTICULAR COMPOUND. IN THE 1790’S, THE STUDY OF MATTER WAS REVOLUTIONIZED BY A NEW EMPHASIS ON THE ‘QUANTITATIVE ANALYSIS’. SCIENTISTS’ INVESTIGATIONS WERE MADE MORE ACCURATE BY NEW IMPROVED MASS BALANCES.

13. ANTOINE LAVOISIER Matter can be neither created nor destroyed! HE BEGAN TO GATHER EVIDENCE ABOUT HOW MATTER BEHAVED BEFORE AND AFTER A REACTION.

14. Matter can be neither created nor destroyed! HE DISCOVERED THAT THE TOTAL MASS OF THE ‘INGREDIENTS’ OF A CHEMICAL REACTION WAS THE SAME AS THE TOTAL MASS OF THE ‘RESULTS’.

15. JOHN DALTON INVESTIGATED TWO OTHER FUNDAMENTAL IDEAS The Law of Definite Proportion

16. The Law of Multiple Proportions

17. CARBON MONOXIDE + = C O CO + = CARBON MONOXIDE C O CO + + = CARBON DIOXIDE O C O CO2

18. IN 1808, JOHN DALTON PROPOSED AN EXPLANATION FOR THE LAW OF THE CONSERVATION OF MASS AND ‘DEFINITE PROPORTIONS. HE ALSO FORMULATED THE LAW OF ‘MULTIPLE PROPORTIONS’. HE REASONED THAT ELEMENTS WERE COMPOSED OF ‘ATOMS’ AND THAT ONLY WHOLE NUMBERS OF ATOMS CAN COMBINE TO FORM COMPOUNDS HIS IDEAS ARE NOW CALLED THE ‘ATOMIC THEORY OF MATTER’ AND CAN BE SUMMARIZEDAS:

19. ELEMENT 1 ELEMENT 2 ELEMENT 3 ELEMENT 4

20. + +

21. DALTON AND HIS CONTEMPORARIES THE EARLIEST THEORISTS THOUGHT THE ATOM WAS HARD AND ROUND, MUCH LIKE TINY MARBLES OR BALL BEARINGS.

22. ALTHOUGH DALTON THOUGHT ATOMS WERE INDIVISIBLE, INVESTIGATORS IN THE LATE 1800’S PROVED OTHERWISE. IT SOON BECAME CLEAR THAT ATOMS ARE ACTUALLY COMPOSED OF SEVERAL BASIC TYPES OF SMALLER PARTICLES. AND IT’S THE NUMBERS AND ARRANGEMENTS OF THESE SUB-ATOMIC PARTICLES THAT DETERMINES THE IDENTITY OF THE ATOM.

23. THE FIRST DISCOVERY OF A SUBATOMIC PARTICLE RESULTED FROM THE INVESTIGATIONS INTO THE RELATIONSHIP BETWEEN ELECTRICITY AND MATTER. IN THE LATE 1800’S, MANY EXPERIMENTS WERE PERFORMED IN WHICH ELECTRIC CURRENT WAS PASSED THROUGH VARIOUS GASES AT LOW PRESSURE. CARRIED OUT IN TUBES CALLED CATHODE-RAY TUBES

24. J.J. THOMPSON Around 1900

27. THOMPSON NOTICED THAT WHEN CURRENT WAS PASSED THROUGH A CATHODE RAY TUBE, THE SURFACE OF THE TUBE DIRECTLY OPPOSITE THE CATHODE GLOWED.

28. CATHODE RAY THOMPSON THEORIZED THAT THE GLOW WAS CAUSED BY A STREAM OF ‘PARTICLES’. HE CALLED THIS STREAM A ‘CATHODE RAY’.

29. CATHODE RAY THE CATHODE RAY TRAVELED FROM THE CATHODE TO THE ANODE WHEN CURRENT WAS PASSED THROUGH THE TUBE. THE CATHODE RAY TUBE OPENED THE DOOR FOR J.J. THOMPSON CATHODE ANODE

32. THOMPSON’S INVESTIGATIONS GAVE EVIDENCE THAT THE CATHODE RAY COULD BE DEFLECTED BY APPLYING A POSITIVELY CHARGED ELECTRIC FIELD. THIS HELPED THOMPSON DISCOVER THAT THE CATHODE RAY WAS ‘NEGATIVELY CHARGED’. +

33. THOMPSON WAS ABLE TO MEASURE THE RATIO OF THE CHARGE OF CATHODE RAY PARTICLES TO THEIR MASS. HE FOUND THAT THE RATIO WAS THE SAME REGARDLESS OF THE METAL USED AS THE CATHODE. THOMPSON CONCLUDED THAT ALL CATHODE RAYS ARE COMPOSED OF IDENTICAL NEGATIVELY CHARGED PARTICLES. WHICH WERE LATER CALLED ELECTRONS.

36. HE PROPOSED THAT THE ATOM LOOKS SOMETHING LIKE A CHOCOLATE CHIP COOKIE. THE CHIPS WOULD BE HIS ‘ELECTRONS’. THE COOKIE PART IS POSITIVE MATTER, TO CANCEL OUT THE NEGATIVE ELECTRONS.

38. THOMPSON WAS ‘ENGLISH’……… HE CALLED HIS MODEL THE ‘PLUM PUDDING ATOM’

39. IN 1909, ROBERT MILLIKAN, PERFORMED AN EXPERIMENT TO CALCULATE THE MASS OF AN ELECTRON. HE DISCOVERED THAT THE MASS OF THE ELECTRON IS ABOUT 1/2000TH THE MASS OF THE SIMPLEST ATOM……HYDROGEN.

41. HIS OIL DROP EXPERIMENT SHOWED THAT EVEN THOUGH THE ATOMS OF DIFFERENT ELEMENTS ARE VERY DIFFERENT, THEIR ELECTRONS ARE IDENTICAL. AN ELECTRON IS AN ELECTRON! THE DIFFERENCE BETWEEN TWO DIFFERENT ATOMS IS THEIR ‘NUMBER’ OF ELECTRONS, NOT THE TYPE OF ELECTRON. HE ALSO CALCULATED THAT THE ELECTRON’S MASS IS 9.109x10-31kg

42. THOMPSON’S & MILLIKAN’S IDEAS ATOMS ARE IN FACT DIVISIBLE. ELECTRONS ARE PRESENT IN ATOMS OF ALL ELEMENTS. ONE OF THE ATOM’S FUNDAMENTAL PARTICLES IS NEGATIVE CHARGED. ATOMS ARE ELECTRICALLY NEUTRAL, SO THERE MUST BE A (+) CHARGE TO BALANCE OUT THE (–). BECAUSE ELECTRONS ARE BASICALLY MASSLESS THERE MUST BE SOMETHING ELSE THAT ACCOUNTS FOR THE ATOMS MASS.

43. BUT, NO ONE KNEW WHAT THE INSIDE OF AN ‘ATOM’ WAS REALLY LIKE UNTIL……

44. ERNEST RUTHERFORD What’s inside an atom? IN 1911, RUTHERFORD PERFORMED ONE OF THE MOST BRILLIANT EXPERIMENTS EVER.

45. IN THE EXPERIMENT, RUTHERFORD SHOT A NARROW BEAM OF ALPHA PARTICLES AT A VERY THIN SHEET OF GOLD FOIL. IF ATOMS WERE LIKE ‘PLUM PUDDING’, THE ALPHA PARTICLES SHOULD HAVE PASSED EASILY THROUGH THE GOLD, WITH ONLY A SLIGHT DEFLECTION. BUT, THAT IS NOT WHAT HAPPENED……

47. WHAT HAPPENED? THE MAJORITY OF THE  PARTICLES PASSED ‘STRAIGHT THROUGH’ THE GOLD ATOMS. MORE SURPRISINGLY, A SMALL NUMBER OF THE  PARTICLES ‘BOUNCED OFF’ THE GOLD FOIL AT VERY LARGE ANGLES. AND SOME EVEN BOUNCED BACK DIRECTLY AT THE SOURCE!