Structure of an Atom

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The Structure of Matter
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PIONEERS OF THE ATOM

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

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THE EARLY ATOM
Its all Greek to me

• DEMOCRITUS IS THE MAN !

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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

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ARISTOTLE SKEPTIC
Democritus is an ignoramus!
ARISTOTLE WAS MUCH MORE POPULAR AND HE OPPOSED
THE IDEA OF ATOMS
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ARISTOTLE SKEPTIC
Democritus is an ignoramus!
ARISTOTLE BELIEVED THAT MATTER WAS CONTINUOUS.
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ARISTOTLES FOUR BASIC ELEMENTSEARTH, AIR, FIRE
and WATER
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BECAUSE OF ARISTOTLES GREAT INFLUENCE
DEMOCRITUS ATOMS
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...ATOMS DIED FOR ABOUT 1,400 YEARS
UNTIL...
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IN THE 1700S
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• 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 PHYSICAL AND
  CHEMICAL PROPERTIES THAN THOSE OF THE ELEMENTS
  THAT FORM THEM.

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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 MASS BALANCES.

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ANTOINE LAVOISIER
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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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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JOHN DALTON INVESTIGATED TWO OTHER FUNDAMENTAL
IDEAS
The Law of Definite Proportion
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The Law of Multiple Proportions
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LAW OF DEFINITE PROPOR-TIONS A CHEMICAL COMPOUND IS ALWAYS COMPOSED OF THE SAME ELEMENTS IN THE SAME PROPORTION BY MASS.
LAW OF DEFINITE PROPOR-TIONS
LAW OF MULTIPLE PROPOR-TIONS IF TWO DIFFERENT COMPOUNDS ARE COMPOSED OF THE SAME TWO ELEMENTS, THEN THE RATIO OF OF THE ELEMENTS IS ALWAYS A RATIO OF SMALL WHOLE NUMBERS.
LAW OF MULTIPLE PROPOR-TIONS
CARBON MONOXIDE


C
O
CO


CARBON MONOXIDE
C
O
CO



CARBON DIOXIDE
O
C
O
CO2
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• 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 SUMMARIZED AS

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ALL MATTER IS COMPOSED OF EXTREMELY SMALL PARTICLES CALLED ATOMS
ATOMS OF A GIVEN ELEMENT ARE IDENTICAL IN SIZE, MASS, AND OTHER PROPERTIES. ATOMS OF DIFFERENT ELEMENTS DIFFER IN SIZE, MASS, OTHER PROPERTIES
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ATOMS CANNOT BE SUBDIVIDED, CREATED, OR DESTROYED.
ATOMS OF DIFFERENT ELEMENTS COMBINE IN SIMPLE WHOLE NUMBER RATIOS TO FORM CHEMICAL COMPOUNDS.
IN CHEMICAL REACTIONS, ATOMS ARE COMBINED, SEPARATED, OR REARRANGED.


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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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• 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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• 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 PRESSURE.
• CARRIED OUT IN TUBES CALLED
• 
  CATHODE-RAY TUBES

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J.J. THOMPSON Around 1900
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• THOMPSON NOTICED THAT WHEN CURRENT WAS PASSED
  THROUGH A CATHODE RAY TUBE, THE SURFACE OF THE
  TUBE DIRECTLY OPPOSITE THE CATHODE GLOWED.

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

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• 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
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• THOMPSONS 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.

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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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• 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.
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THOMPSON WAS ENGLISH HE CALLED HIS MODEL
THE PLUM PUDDING ATOM
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• 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
  ATOMHYDROGEN.

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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 THE TYPE OF
  ELECTRON.
• HE ALSO CALCULATED THAT THE ELECTRONS MASS IS
  9.109x10-31kg

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• THOMPSONS MILLIKANS IDEAS
• ATOMS ARE IN FACT DIVISIBLE.
• ELECTRONS ARE PRESENT IN ATOMS OF ALL ELEMENTS.
• ONE OF THE ATOMS 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.

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BUT, NO ONE KNEW WHAT THE INSIDE OF AN ATOM WAS
REALLY LIKE UNTIL
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ERNEST RUTHERFORD
Whats inside an atom?
IN 1911, RUTHERFORD PERFORMED ONE OF THE MOST
BRILLIANT EXPERIMENTS EVER.
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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
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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!
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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. HE CONCLUDED THAT ALL THE
POSITIVE CHARGE AND ALMOST ALL THE MASS IS
CONCENTRATED IN A SMALL CORE CALLED THE NUCLEUS.
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IN 1932, THE ENGLISH PHYSICIST JAMES CHADWICK
CONFIRMED THE EXISTANCE OF YET ANOTHER SUBATOMIC
PARTICLE THE NEUTRON. A PARTICLE WITH NO
CHARGE. IT HAS A MASS NEARLY EQUAL TO THAT OF
THE PROTON. THEREFORE, THE SUBATOMIC PARTICLES
ARE THE ELECTRON, PROTON, AND NEUTRON.
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electron e- -1 0 9.11x10-28
proton p 1 1 1.67x10-24
neutron n0 0 1 1.67x10-24
Properties of Subatomic Particles
RELATIVE
RELATIVE
ACTUAL
SYMBOL
CHARGE
PARTICLE
MASS (g)
MASS
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A LITTLE REVIEW
THERE ARE THREE FUNDAMENTAL PARTICLES THAT MAKE
UP THE ATOM. THEY ARE ELECTRONS, PROTONS, AND
NEUTRONS. THE PROTONS AND THE NEUTRONS MAKE UP
THE CENTER OF THE ATOM, WHICH IS CALLED THE
NUCLEUS. THE PROTONS NEUTRONS MAKE UP 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 NUMBER IS 8. THE PROTONS
IDENTIFY THE TYPE OF ATOM, THE ONLY ATOM WITH 8
PROTONS IS OXYGEN.
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ATOMS OF THE FIRST TEN ELEMENTS ATOMS OF THE FIRST TEN ELEMENTS ATOMS OF THE FIRST TEN ELEMENTS ATOMS OF THE FIRST TEN ELEMENTS ATOMS OF THE FIRST TEN ELEMENTS ATOMS OF THE FIRST TEN ELEMENTS ATOMS OF THE FIRST TEN ELEMENTS

Hydrogen H 1 1 0 1 1
Helium He 2 2 2 4 2
Lithium Li 3 3 4 7 3
Beryllium Be 4 4 5 9 4
Boron B 5 5 6 11 5
Carbon C 6 6 6 12 6
Nitrogen N 7 7 7 14 7
Oxygen O 8 8 8 16 8
Fluorine F 9 9 10 19 9
Neon Ne 10 10 10 20 10
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 ELECTRON. AN OXYGEN ATOM HAS
8 ELECTRONS. THE MASS OF AN ATOM IS CONCENTRATED
IN ITS NUCLEUS AND DEPENDS ON THE NUMBER 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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SODIUM ISOTOPES
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EXAMPLE OF AN ISOTOPE
ATOMIC MASS
ATOMIC NUMBER
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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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LOST AN ELECTRON CHARGE
GAINED AN ELECTRON - CHARGE
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SOME ATOMS GAIN ELECTRONS
ATOMS IONIC CHARGE NUMBER OF PROTONS NUMBER
OF ELECTRONS
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
O-2
O
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ATOMS, IONS, AND ISOTOPES ATOMS, IONS, AND ISOTOPES
ATOMS NEUTRAL AND ARE DEFINED BY THE OF PROTONS IN THEIR NUCLEUS
ATOMS 3 p Li ATOM, ETC.
IONS HAVE AN ELECTRICAL CHARGE DETERMINED BY PROTONS - ELECTRONS
IONS N-2 7 p - 9 e- ETC.
ISOTOPES TWO ATOMS WITH THE SAME OF PROTONS, BUT DIFFERENT S OF NEUTRONS OR MASSES
ISOTOPES CALCIUM-40 CALCIUM-44
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NIELS BOHR INVESTGATED THE ARRANGEMENT OF
ELECTRONS
How are electrons arranged inside an atom?
BOHR FOUND THAT ELECTRONS TRAVEL IN DISCRETE
ORBITS ABOUT THE NUCLEUS. THE CHEMICAL
PROPERTIES OF AN ATOM ARE DETERMINED BY THE
NUMBER OF ELECTRONS IN AN ATOMS OUTER ORBIT.
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ELECTRON SHELLS AND ATOMIC STRUCTURE
THE FIRST SHELL WILL HOLD UP TO 2 ELECTRONS. THE
SECOND AND THIRD SHELLS WILL HOLD UP TO 8
ELECTRONS. SOMETIMES SHELLS ARE MADE OF
SUB-SHELLS. ATOMS WITH ELECTRONS OUTSIDE OF
FILLED SHELLS OR WITH MISSING ELECTRONS ARE VERY
CHEMICALLY REACTIVE.
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ATOMS WITH FILLED SHELLS ARE STABLE, OR
NON-REACTIVE. THESE ARE CALLED INERT
GASES
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