THE STRUCTURE OF THE ATOM

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THE STRUCTURE OF THE ATOM

• ATOMIC MODELS

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PIONEERS OF THE ATOM

• DEMOCRITUS
• LAVOISIER
• DALTON
• THOMPSON
• MILLIKEN
• RUTHERFORD

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THE EARLY ATOM
ITS ALL GREEK TO ME...

• DEMOCRITUS IS THE MAN!!!
• YOU KNOW IT!

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DEMOCRITUS

• WAS A GREEK PHILOSOPHER THAT BEGAN WONDERING WHAT
  WAS THE UNIVERSE MADE UP OF.
• HE PROPOSED THAT ALL THE MATTER IN THE UNIVERSE
  IS COMPOSED OF TINY PARTICLES
• THESE PARTICLES ARE INDIVISABLE
• HE CALLED THESE PARTICLES ATOMOS (MEANS
  INDIVISABLE)
• BUT HE HAD AN OPPONENT

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ARISTOTLE SCEPTIC
DEMOCRITUS IS AN IGNORAMUS!
ARISTOTLE WAS MUCH MORE POPULAR AND HE OPPOSED
THE IDEA OF ATOMS!
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ARISTOTLE SCEPTIC
DEMOCRITUS IS AN IGNORAMUS!
ARISTOTLE BELIEVED THAT MATTER WAS CONTINUOUS.
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DEMOCRITUS ATOMS
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SO...CHEMISTRY DIED FOR ABOUT 1400 YEARS
UNTIL...
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SO...CHEMISTRY DIED FOR ABOUT 1400 YEARS
IN THE 1700S
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FOUNDATIONS OF ATOMIC THEORY

• THE PREDOMINATE BELIEF BY THE MID 1700S 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 PHYS AND CHEM
  PROPERTIES THAN THOSE OF THE ELEMENTS THAT FORM
  THEM.

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FOUNDATIONS OF ATOMIC THEORY

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

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ANTOINNE LAVOISIER TOOK ADVANTAGE
MATTER CAN BE NEITHER CREATED NOR DESTROYED.
HE BEGAN TO GATHER EVIDENCE ABOUT HOW MATTER
BEHAVED BEFORE AND AFTER A REACTION.
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ANTOINNE LAVOISIER TOOK ADVANTAGE
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
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2 OTHER FUNDAMENTAL IDEAS
WERE INVESTIGATED...
THE LAW OF DEFINITE PROPORTION
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2 OTHER FUNDAMENTAL IDEAS
WERE INVESTIGATED...
THE LAW OF MULTIPLE PROPORTIONS
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2 OTHER FUNDAMENTAL IDEAS
WERE INVESTIGATED...
IM BETTER LOOKING THAN PROUST!
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CARBON MONOXIDE
C
O
CO


CARBON MONOXIDE
C
O
CO



CARBON DIOXIDE
O
C
O
CO2
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DALTONS THOUGHTS

• IN 1808, JOHN DALTON PROPOSED AN EXPLANATION FOR
  THE LAW OF CONS OF MASS, THE LAW OF DEFINITE
  PROPORTIONS, FORMULATED THE LAW OF MULTIPLE
  PROPORTIONS.
• HE REASONED THAT ELEMENTS WERE COMPOSED OF ATOMS
  THAT ONLY WHOLE S OF ATOMS CAN COMBINE TO
  FORM COMPNDS
• HIS THEORY CAN BE SUMMARIZED IN 5 STATEMENTS.

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

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

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STRUCTURE OF THE ATOM

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

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STRUCTURE OF THE ATOM

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

CATHODE RAY TUBE
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STRUCTURE OF THE ATOM

• THEY HYPOTHESIZED THAT THE GLOW WAS CAUSED BY A
  STREAM OF PARTICLES
• THEY CALLED THE STREAM A CATHODE RAY

CATHODE RAY TUBE
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STRUCTURE OF THE ATOM

• 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
CATHODE RAY TUBE
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J. J. THOMPSON
I PLAY WITH ELECTRONS
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J. J. THOMPSON

• THOMPSONS INVESTIGATIONS SUPPLIED EVIDENCE THAT
  THE CATHODE RAY COULD BE DEFLECTED BY APPLYING A
  POSITIVELY CHARGED ELECTRIC FIELD
• THIS HELPED THOMPSON
  DISC- OVER THAT THE
  CATHODE RAY WAS
  NEGATIVELY CHARGED.

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• 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

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THOMPSONS ATOMIC MODEL

• HE PROPOSED THAT THE ATOM LOOKS SOMETHING LIKE A
  CHOCOLATE CHIP COOKIE

THE CHIPS WOULD BE HIS ELECTRONS
THE COOKIE PART IS POS. MATTER TO CANCEL OUT THE
NEG. ELECTRONS
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• THOMPSONS EXPERIMENTS REVEALED THAT THE ELECTRON
  HAS A VERY LARGE CHARGE IN RELATION TO ITS MASS
• IN 1909, ROBERT MILLIKAN, PERFORMED AN INGENIOUS
  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
  (HYDRO.)

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HELLO, MILLIKAN
DATS RIGHT! I SAVED THE DAY!
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• 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 THEIR TYPE OF
  ELECTRON.
• HE ALSO CALCULATED THAT THE ELECTRONS MASS IS
  9.109x10-31kg

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SO FAR WEVE LEARNED

• THOMPSONS MILLIKANS IDEAS
• ATOMS ARE IN FACT DIVISABLE
• ELECTRONS ARE PRESENT IN ATOMS OF ALL ELEM.
• ONE OF THE ATOMS FUNDMNTL PARTICLES IS NEG.
  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.

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OTHER SIGNIFICANT DISCOVERIES

• IN 1886, WHEN E. GOLDSTEIN OBSERVED A CATHODE-RAY
  TUBE AND FOUND RAYS TRAVELLING IN THE OPPOSITE
  DIRECTION OF THAT OF THE CATHODE RAYS
• HE CALLED THE RAYS CANAL RAYS AND CONCLUDED THAT
  THEY WERE COMPOSED OF POS. PARTICLES
• IT WAS SOON DISCOVERED THAT THE POSITIVE
  PARTICLES MASS IS ABOUT 2000 TIMES THAT OF THE
  ELECTRON

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OTHER SIGNIFICANT DISCOVERIES

• IN 1932, THE ENGLISH PHYSICIST JAMES CHADWICK
  CONFIRMED THE EXISTANCE OF YET ANOTHER SUBATOMIC
  PARTICLE.
• THE NEUTRON, WHICH IS A PARTICLE WITH NO CHARGE
• HAS A MASS NEARLY EQUAL TO THAT OF THE PROTON
• THEREFORE THE SUBATOMIC PARTICLES ARE THE
  ELECTRON, PROTON, AND NEUTRON.

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Properties of Subatomic Particles
RELATIVE
RELATIVE
ACTUAL
SYMBOL
CHARGE
PARTICLE
MASS (g)
MASS
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THE ATOMIC NUCLEUS

• WHEN SUBATOMIC PARTICLES WERE DISCOVERED,
  SCIENTISTS WONDERED HOW THESE PARTICLES WERE PUT
  TOGETHER IN AN ATOM.
• THIS WAS A DIFFICULT QUESTION TO ANSWER, GIVEN
  HOW TINY ATOMS ARE.
• MOST SCIENTISTS THOUGHT IT LIKELY THAT THE
  ELECTRONS WERE EVENLY DISTRIBUTED THROUGHOUT AN
  ATOM FILLED UNIFORMLY WITH POSITIVELY CHARGED
  MATERIAL.

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ERNEST RUTHERFORD
HOW IS THE ATOM BUILT?
IN 1911, RUTHERFORD PERFORMED ONE OF THE MOST
BRILLIANT INVESTIGATIONS EVER CONCIEVED.
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RUTHERFORDS FAMOUS EXPERIMENT

• RUTHERFORD SET OUT TO TEST THE THOMPSON MODEL OF
  THE ATOM
• THE TEST USED RELATIVELY MASSIVE RADIOACTIVE
  ALPHA PARTICLES
• ALPHA PARTICLES (?) ARE HELIUM ATOMS THAT HAVE
  LOST THEIR 2 ELECTRONS AND HAVE A DOUBLE
  POSITIVE CHARGE BECAUSE OF THE 2 REMAINING PROTONS

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• IN THE EXPERIMENT, RUTHERFORD DIRECTED A NARROW
  BEAM OF ALPHA PARTICLES AT A VERY THIN SHEET OF
  GOLD FOIL.
• ACCORDING TO THE PREVAILING THEORY, THE ALPHA
  PARTICLES SHOULD HAVE PASSED EASILY THROUGH THE
  GOLD, WITH ONLY A SLIGHT DEFLECTION DUE TO THE
  POSITIVE CHARGE THOUGHT TO BE SPREAD OUT IN THE
  GOLD ATOMS.

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WHAT HAPPENED?

• THE MAJORITY OF THE ? PARTICLES PASSED STRAIGHT
  THROUGH THE GOLD ATOMS, WITHOUT ANY DEFLECTION
• EVEN MORE SURPRISINGLY, A SMALL FRACTION OF THE ?
  PARTICLES BOUNCED OFF THE GOLD FOIL ATOMS AT VERY
  LARGE ANGLES
• SOME EVEN BOUNCED BACK AT THE SOURCE

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• BASED ON THE RESULTS, RUTHERFORD SUGGESTED A NEW
  THEORY OF THE ATOM.
• HE PROPOSED THAT THE ATOM IS MOSTLY EMPTY SPACE
• THIS EXPLAINED THE LACK OF DEFLECTION OF SOME OF
  THE PARTICLES
• HE CONCLUDED THAT ALL THE POSITIVE CHARGE AND
  ALMOST ALL THE MASS IS CONCENTRATED IN A SMALL
  CORE
• HE CALLED THIS REGION THE NUCLEUS

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WHAT DO WE KNOW?

• THERE ARE THREE FUNDAMENTAL PARTICLES THAT
  TOGETHER MAKE UP THE ATOM.
• COMPOSED OF ELECTRONS, PROTONS, AND NEUTRONS
• THE PROTONS AND THE NEUTRONS MAKE UP THE CENTER
  OF THE ATOM
• CENTER OF THE ATOM IS CALLED THE NUCLEUS
• THE PROTONS NEUTRONS OCC-UPY THE MASS OF THE
  ATOM

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• THE ELECTRONS SURROUND THE NUCLEUS AND OCCUPY
  MOST OF THE ATOMS VOLUME
• HOW, THEN, ARE ATOMS OF HYDROGEN DIFFERENT FROM
  THOSE OF OXYGEN?
• A SUBATOMIC PARTICLES FROM ONE TYPE OF ATOM LOOKS
  LIKE PARTICLES FROM OTHER ATOMS

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• ITS THE NUMBERS OF PROTONS IN AN ATOM THAT MAKES
  ATOMS DIFFERENT.
• AN OXYGEN ATOM HAS 8 PROTONS IN ITS NUCLEUS
• A HYDROGEN ATOM HAS 1 PROTON IN ITS NUCLEUS
• THE ATOMIC NUMBER OF AN ELEMENT IS THE NUMBER OF
  PROTONS IN THE NUCLEUS OF AN ATOM OF THAT ELEMENT
• SINCE OXYGENS NUCLEUS HAS 8 PROTONS ITS
  ATOMIC IS 8
• THE PROTONS IDENTIFY THE TYPE OF ATOM, THE ONLY
  ATOM WITH 8 PROTONS IS OXYGEN

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SYMBOL
ATOMIC
PROTONS
NEUTRONS
MASS
ELECTRONS
NAME
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• FOR EACH ELEMENT LISTED, THE NUMBER OF PROTONS
  EQUALS THE NUMBER OF ELECTRONS
• REMEMBER ATOMS ARE ELECTRICALLY NEUTRAL
• IN AN ATOM, THE NUMBER OF ELECTRONS MUST EQUAL
  THE NUMBER OF PROTONS
• A HYDROGEN ATOM HAS 1 ELECTRN
• AN OXYGEN ATOM HAS 8 ELECTRNS
• THE MASS OF AN ATOM IS CONCEN. IN ITS NUCLEUS AND
  DEPENDS ON THE NUMER OF PROTONS AND NEUTRONS

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• THE TOTAL NUMBER OF PROTONS AND NEUTRONS IN AN
  ATOM IS CALLED THE MASS NUMBER
• A CARBON ATOM, WHICH HAS 6 PROTONS AND 6
  NEUTRONS, HAS A MASS NUMBER OF 12
• IF YOU KNOW THE ATOMIC NUMBER AND MASS NUMBER OF
  AN ATOM OF ANY ELEMENT, YOU CAN DETERMINE THE
  ATOMS COMPOSITION
• THE COMPOSITION OF ANY ATOM CAN BE REPRESENTED IN
  SHORTHAND NOTATION

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CHEMICAL COMPOSITION SHORTHAND
OF PROTONS OF NEUTRONS
Cl
MASS NUMBER
35
ATOMIC NUMBER
17
NUMBER OF PROTONS
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ISOTOPES

• EVERY CHLORINE ATOM HAS 17 PROTONS, WITHOUT
  EXCEPTION,
• HOWEVER, NOT EVERY CHLORINE ATOM HAS 18 NEUTRONS.
• ATOMS WITH THE SAME NUMBER OF PROTONS BUT CONTAIN
  DIFFERENT NUMBERS OF NEUTRONS ARE CALLED
  ISOTOPES.
• BECAUSE ISOTOPES OF AN ELEMENT HAVE DIFFERENT
  NUMBERS OF NEUTRONS THEY HAVE DIFFERENT MASS
  NUMBERS.

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• ISOTOPES ARE CHEMICALLY ALIKE BECAUSE THEY HAVE
  IDENTICAL NUMBERS OF PROTONS AND ELECTRONS
• ITS THE ELECTRONS AND PROTONS THAT ARE
  RESPONSIBLE FOR CHEMICAL BEHAVIOR

BERYLLIUM ISOTOPES
proton
neutron
electron
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EXAMPLE OF AN ISOTOPE
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IONS

• AN ELEMENTS ATOMS ARE NOT ALWAYS NEUTRAL IN
  CHARGE.
• WHEN AN ATOM LOSES OR GAINS ONE OR MORE OF ITS
  ELECTRONS IT BECOMES ION.
• AN ION THAT HAS MORE ELECTRONS THAN PROTONS HAS A
  NEGATIVE ELECTRICAL CHARGE
• AN ION THAT HAS FEWER ELECTRONS THAN PROTONS HAS
  A POSITIVE ELECTRICAL CHARGE

NOTE ITS THE PROTONS THAT DEFINE THE TYPE OF
ATOM IT IS, BUT THE ELECTRONS DEFINE THE ATOMS
CHARGE.
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SOME ATOMS GAIN ELECTRONS
ATOMS IONIC CHARGE PROTONS - ELECTRONS
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
O-2
O
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ATOMIC MASS

• THE ACTUAL MASS OF A PROTON OR A NEUTRON IS VERY
  SMALL
• 1.67x10-24 g
• THE PROTONS NEUTRONS IS THE MASS OF THE ATOM
• THEREFORE THE MASS OF EVEN THE LARGEST ATOM IS
  INCREDIBALLY SMALL
• SCIENTISTS HAVE DETERMINED THE TINY MASSES OF
  ATOMS BY USING AN INSTRUMENT CALLED A MASS
  SPECTROMETER.

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• FINDING THE MASS OF AN INDIVIDUAL ATOM CAN
  PROVIDE USEFUL INFO, BUT IN GENERAL, THESE VALUES
  ARE TOO SMALL AND IMPRACTICAL TO WORK WITH.
• INSTEAD SCIENTISTS COMPARE THE RELATIVE MASSES OF
  ATOMS TO A REFERENCE ATOM.
• A STANDARD HAS BEEN SET THAT DEFINES THE MASS OF
  ALL THE OTHER ATOMS
• THE ISOTOPE CHOSEN WAS THE CARBON-12 ATOM.

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• THIS ISOTOPE OF CARBON WAS ASSIGNED A MASS OF
  EXACTLY 12 ATOMIC MASS UNITS
• 1 ATOMIC MASS UNIT (amu) IS DEFINED AS 1/12TH THE
  MASS OF AN CARBON-12 ATOM.
• USING THAT INFORMATION WE CAN SAY THAT A HELIUM-4
  ATOM HAS A MASS 1/3 THE MASS OF C-12
• A CARBON-12 ATOM HAS 6 PROTONS AND 6 NEUTRONS IN
  ITS NUCLEUS, AND ITS MASS IS SET AS 12 amu.

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• THE 12 PROTONS AND NEUTRONS ACCOUNT FOR NEARLY
  ALL OF CARBONS MASS
• THEREFORE, THE MASS OF A SINGLE PROTON OR A
  SINGLE NEUTRON HAS A MASS OF 1amu.
• SINCE THE MASS OF AN ATOM IS BASED ON INDIVIDUAL
  PARTICLES OF MATTER, THE ATOMIC MASS OF AN ATOM
  SHOULD BE A WHOLE NUMBER
• YET ON THE PERIODIC TABLE THE MASSES ARENT WHOLE
  NUMBERS

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• THE MASSES ON THE PERIODIC TABLE ARE WEIGHTED
  AVERAGES
• IN NATURE, MOST ELMNTS EXIST AS A MIXTURE OF
  ISOTOPES
• EACH ISOTOPE OF AN ELEMENT HAS A FIXED MASS AND A
  NATURAL ABUNDANCE.
• NATURAL ABUNDANCE IS AN INDICATION OF HOW OFTEN
  WE WOULD ENCOUNTER A PARTICULAR ISOTOPE
• ONE OF THE ISOTOPES IS ALMOST ALWAYS ENCOUNTERED
  MORE OFTEN SO IT GETS MORE WEIGHT

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• RECALL THAT THE ELEMENT Cl HAS 2 ISOTOPES (Cl-35
  Cl-37)
• 75 OF THE CHLORINE ATOMS YOULL FIND IN NATURE
  ARE Cl-35
• WHICH HAS 17 PROTONS AND 18 NEUTRONS IN ITS
  NUCLEUS
• 25 OF THE CHLORINE ATOMS YOULL FIND IN NATURE
  ARE Cl-37
• WHICH HAS 17 PROTONS AND 20 NEUTRONS IN ITS
  NUCLEUS.
• SINCE WE ARE MORE LIKELY TO FIND A Cl-35 ATOM THE
  AVERAGE MASS OF Cl IS CLOSER TO 35 THAN TO THE
  TRUE AVERAGE OF 36.

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• THEREFORE, THE ATOMIC MASS OF AN ATOM IS THE
  WEIGHTED AVERAGE MASS OF THE ATOMS IN A NATURALLY
  OCCURRING SAMPLE OF THE ELEMENT
• THE MASS NUMBER OF AN ATOM IS THE PROTONS
  NEUTRONS OF A PARTICULAR ATOM
• IF WE NEED THE MASS NUMBER FROM THE PERIODIC
  TABLE WE TAKE THE CLOSEST
  WHOLE NUMBER TO THE
  ATOMIC MASS FOUND ON
  THE PERIODIC TABLE.