WHAT’S THE MATTER?. CONSERVATION OF MASS LAVOISIER SHOWED BY METICULOUS MEASUREMENT OF THE MASS OF...

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)