WHAT’S THE MATTER?
THE ANCIENT ELEMENTS
•AIR•EARTH•WATER•FIRE
•GAS•SOLID•LIQUID•PLASMA
CHANGES OF STATE
SOLID
TO LIQUID
TO GAS
TO PLASMA
PLUS FUSION ENERGY
PLUS EVAPORATION ENERGY
PLUS IONIZATION ENERGY
CONSERVATION OF MASS
LAVOISIER SHOWED BY METICULOUSMEASUREMENT OF THE MASS OF THINGSAS 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: 460-348 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 10-19 COULOMBSEASY TO CALCULATE THE MASS 9.1x10-31 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 NEUTRALTHE 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 HOWALPHA PARTICLES INTERACT WITH MATTER
Lead sheet
Gold foil
scintillator
Source ofalpha particles
LIKE BOUNCING A CANNONBALL OF A KLEENEX!!
Small scatterexpected
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
Mp=1.67X10-27 kg Mn=1.68X10-27 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 RADIATIONEMITTED 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 OXYGENH2O
ONE CARBON AND TWO OXYGENSCO2
PERIODIC TABLE
ONE OF NATURE’S GREAT PATTERNS
PERIODIC TABLE
ORDER IN THE PERIODIC TABLEGROUPS OF ELEMENTS WITH SIMILAR PROPERTIESROUGHLY CORRESPONDING TO INCREASING MASS
BUT NO SOLID THEORETICAL BASIS.
PERIODIC TABLE
ROENTGEN, BAVARIA 1895WORKING ON CATHODE RAY TUBEDISCOVERED X-RAYS4-DAYS AFTER NEWS REACHED USA, FOUND A BULLET IN A MAN’S LEG
FIRST NOBEL PRIZE 1901 TO ROENTGENLAWS 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-RAYSBARKLA FOUND X-RAYS CAME IN A SERIESOF VARIABLE PENETRATION STRENGTHSHIGHER 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 GRATINGBUT 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-RAYSCAME FROM WHICH MATERIALS, USING BRAGGDIFFRACTION TO MEASURE WAVELEGTHS
MOSELEY FOUND THAT WAVELENGTH DECREASEDWITH INCREASING ATOMIC WEIGHTIN A PRECISE PATTERN L=cM2
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 DETERMINEWHAT MATERIAL HE WAS LOOKING AT
HE ALSO COULD PREDICT THAT THERE WERE SIX MISSING ELEMENTS IN THE PERIODIC TABLE, AND EXACTLY WHAT THEIRATOMIC NUMBER SHOULD BE
MOSELEY PROPOSED THAT THERE WAS ASPECIFIC NUMBER FOR EACH ELEMENTHE CALLED THIS THE ATOMIC NUMBER
PERIODIC TABLE
MOSELEY ACTUALLY IDENTIFIED THE NUMBER OF PROTONS IN THE NUCLEUSTHE EXTRA WEIGHT WAS MADE UP OF THE NEUTRONS.
PERIODIC TABLE
NOBEL PRIZES
1914 VON LAUE X-RAY DIFFRACTION1915 BRAGG WAVELENGTH OF X-RAYS1916 NO MEDAL AWARDED (WW I)1917 BARKLA DIFFERENT STRENGTHS
OF X-RAYS FROMDIFFERENT MATERIALS
MOSELEY WAS KILLED AT GALLIPOLION AUG 10, 1915. 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/D2 ELECTROMAGNETIC FORCE: 1/D2
[4.17x1042 STRONGER THAN GRAVITY]WEAK FORCE (INVOLVED IN RADIOACTIVITY)STRONG (HOLDS NUCLEUS TOGETHER) 100X STRONGER THAN E/M, RANGE 10-15 m
FORCES ACT THROUGH THE EXCHANGE OF PARTICLES (GRAVITONS, PHOTONS, GLUONS)