WHAT’S THE MATTER?

CONSERVATION OF MASS LAVOISIER SHOWED BY METICULOUS MEASUREMENT OF THE MASS OF THINGS AS THEY UNDERWENT DECAY, CORROSION, COMBUSTION, OR ANY OTHER TRANSFORMATION, THAT THE TOTAL MASS OF A CLOSED SYTEM IS CONSTANT. THAT IS MASS CAN NEITHER BE CREATED NOR DESTROYED. LAVOISIER WAS BEHEADED BY MARAT IN 1793

ATOMS DEMOCRITUS: B.C. CONCEPT OF THE ATOM: SMALLEST INDIVISIBLE PARTICLE “Nothing exists nut atoms and empty space; all else is opinion” MID 1800’S: ATOMS ARE NOT INDIVISIBLE ATOMIC PARTICLES: PROTONS, NEUTRONS AND ELECTRONS

DISCOVERY OF THE ELECTRON 1899 THOMSON MEASURED THE CHARGE/MASS RATIO OF AN ELECTRON 1909 MILLIKEN MEASURED THE ELECTRON CHARGE q= -1.6 x COULOMBS EASY TO CALCULATE THE MASS 9.1x kg IT WAS ASSUMED THE ELECTRONS WERE IMBEDDED IN A POSITIVE MATRIX

ELECTRONS MICHAEL FARADAY: SHOWED THAT ELECTRONS COULD BE CAUSED TO FLOW, COULD BE DEFLECTED, AND HAD NEGATIVE CHARGE SINCE ATOMS ARE ELECTRICALLY NEUTRAL THE NUCLEUS MUST HAVE A POSITIVE CHARGE ELECTRONS HAVE MASS BUT ARE 1860x LIGHTER THAN PROTONS

DISCOVERY OF THE NUCLEUS RUTHERFORD (AT McGILL for 7 years) STUDIED HOW ALPHA PARTICLES INTERACT WITH MATTER Lead sheet Gold foil scintillator Source of alpha particles LIKE BOUNCING A CANNONBALL OF A KLEENEX!! Small scatter expected High angle scattering

NUCLEUS MASS OF ALPHA PARTICLE = 8000 ELECRONS MATTER MUST HAVE SMALL DENSE NUCLEI THESE NUCLEI HAVE POSITIVE CHARGE ELECTRONS ARE IN ORBIT AROUND THE NUCLEI BUT! ACCELERATING CHARGES LOSE ENERGY!!!

THE NUCLEUS PROTONS CARRY THE POSITIVE CHARGE NEUTRONS CARRY EXTRA MASS IN NUCLEUS ISOTOPES ARE ATOMS WITH THE SAME NUMBER OF PROTONS BUT DIFFERENT NUMBERS OF NEUTRONS M p =1.67X kg M n =1.68X kg IF P~N ATOMS ARE STABLE

ATOMIC THEORY MATTER IS MOSTLY NOTHING NUCLEUS Electron orbitals

ATOMIC DECAY WHEN RADIO-ACTIVE ATOMS DECAY (TRANSMUTE) THEY EMIT 3 KINDS OF RADIATION ALPHA PARTICLE = He ATOMS p+ BETA PARTICLE = ELECTROMS e- GAMMA RAYS = HIGH ENERGY PHOTONS ALL NUCLEAR DECAY HAS A CHARACTERISTIC HALF-LIFE (WHEN HALF OF NUCLEI ARE LEFT)

RADIOACTIVITY 1896 BECQUEREL STUDIED THE RADIATION EMITTED FROM URANIUM SALTS HE FOUND THREE TYPES OF RADIATION BETA RAYS - ELECTRONS (-VE CHARGE) GAMMA RAYS - LIKE X-RAYS ALPHA RAYS - He NUCLEI - +2 CHARGE

ELEMENTS DIFFERENT ATOMS EXHIBIT DIFFERENT PROPERTIES

COMPOUNDS COMPOUNDS ARE COMBINATIONS OF ATOMS ATOMS COMBINE IN FIXED RATIOS TWO HYDROGENS AND ONE OXYGEN H 2 O ONE CARBON AND TWO OXYGENS CO 2

PERIODIC TABLE ONE OF NATURE’S GREAT PATTERNS

PERIODIC TABLE ORDER IN THE PERIODIC TABLE GROUPS OF ELEMENTS WITH SIMILAR PROPERTIES ROUGHLY CORRESPONDING TO INCREASING MASS BUT NO SOLID THEORETICAL BASIS.

PERIODIC TABLE ROENTGEN, BAVARIA 1895 WORKING ON CATHODE RAY TUBE DISCOVERED X-RAYS 4-DAYS AFTER NEWS REACHED USA, FOUND A BULLET IN A MAN’S LEG FIRST NOBEL PRIZE 1901 TO ROENTGEN LAWS PASSED TO BAN X-RAYS FROM OPERA GLASSES

PERIODIC TABLE X-RAYS EMITTED WHEN ELECTRONS STRUCK GLASS WALL OF CATHODE RAY TUBE; WHAT ABOUT OTHER MATERIALS? METALS CAUSE MORE X-RAYS BARKLA FOUND X-RAYS CAME IN A SERIES OF VARIABLE PENETRATION STRENGTHS HIGHER STRENGTH FROM HEAVIER METALS

PERIODIC TABLE BUT WHAT ARE THESE MYSTERIOUS RAYS? PARTICLES LIKE ELECTRONS? WAVES, LIKE LIGHT? IF WAVES, CAN BE DIFFRACTED BY A GRATING BUT GRATING WOULD HAVE TO BE INCREDIBLY SMALL VON LAUE: WHY NOT USE CRYSTAL AS GRATING?

PERIODIC TABLE X-RAYS ARE DIFFRACTED BY CRYSTALS! X-RAYS ARE AN ENERGETIC FORM OF LIGHT BRAGG: DIFFERENT CRYSTALS OF DIFFERENT ATOMIC SPACING ALLOW FOR THE CALCULATION OF THE WAVELENGTH OF THE X-RAYS

PERIODIC TABLE MOSELEY: DECIDED TO FIND OUT WHAT X-RAYS CAME FROM WHICH MATERIALS, USING BRAGG DIFFRACTION TO MEASURE WAVELEGTHS MOSELEY FOUND THAT WAVELENGTH DECREASED WITH INCREASING ATOMIC WEIGHT IN A PRECISE PATTERN L=cM 2

PERIODIC TABLE THE MASSES OF THE ELEMENTS IN THE PERIODIC TABLE DID NOT INCREASE IN ANY LOGICAL WAY 40.1, 47.9, 50. 9, 52, 54.9, ETC

PERIODIC TABLE MOSELEY COULD USE X-RAYS TO DETERMINE WHAT MATERIAL HE WAS LOOKING AT HE ALSO COULD PREDICT THAT THERE WERE SIX MISSING ELEMENTS IN THE PERIODIC TABLE, AND EXACTLY WHAT THEIR ATOMIC NUMBER SHOULD BE MOSELEY PROPOSED THAT THERE WAS A SPECIFIC NUMBER FOR EACH ELEMENT HE CALLED THIS THE ATOMIC NUMBER

PERIODIC TABLE MOSELEY ACTUALLY IDENTIFIED THE NUMBER OF PROTONS IN THE NUCLEUS THE EXTRA WEIGHT WAS MADE UP OF THE NEUTRONS.

PERIODIC TABLE NOBEL PRIZES 1914VON LAUE X-RAY DIFFRACTION 1915BRAGGWAVELENGTH OF X-RAYS 1916NO MEDAL AWARDED (WW I) 1917BARKLADIFFERENT STRENGTHS OF X-RAYS FROM DIFFERENT MATERIALS MOSELEY WAS KILLED AT GALLIPOLION AUG 10, NOBEL PRIZES ARE AWARDED ONLY TO LIVING SCIENTISTS.

ELECTRONS ARE THE KEY TO ALL CHEMISTRY ELECTRONS FORM CHEMICAL BONDS ELECTRONS COME IN “SHELLS” PAULI’S EXCLUSION PRINCIPLE: TWO ELECTRONS CANNOT OCCUPY THE SAME STATE

SUB-ATOMIC PHYSICS PROTONS AND NEUTRONS ARE MADE UP OF QUARKS (predicted in 1960; observed experimentally in 1969) THERE ARE SIX TYPES OF QUARKS (FLAVOURS) UP, DOWN, STRANGE, CHARM, BOTTOM AND TOP

FUNDAMENTAL FORCES GRAVITY: RANGE INFINITE, WEAK, 1/D 2 ELECTROMAGNETIC FORCE: 1/D 2 [4.17x10 42 STRONGER THAN GRAVITY] WEAK FORCE (INVOLVED IN RADIOACTIVITY) STRONG (HOLDS NUCLEUS TOGETHER) 100X STRONGER THAN E/M, RANGE m FORCES ACT THROUGH THE EXCHANGE OF PARTICLES (GRAVITONS, PHOTONS, GLUONS)