Download ATOMS

PIONEERS OF THE ATOM
DEMOCRITUS
LAVOISIER
DALTON
THOMPSON
MILLIKEN
RUTHERFORD
BOHR
THE EARLY ATOM
It’s all Greek
to me ……
DEMOCRITUS IS
THE MAN !
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……
ARISTOTLE = SKEPTIC
Democritus is
an ignoramus!
ARISTOTLE WAS
MUCH MORE
POPULAR AND HE
OPPOSED THE IDEA
OF ‘ATOMS’
ARISTOTLE = SKEPTIC
Democritus is
an ignoramus!
ARISTOTLE
BELIEVED THAT
MATTER WAS
‘CONTINUOUS’.
ARISTOTLE’S FOUR BASIC ELEMENTS
EARTH, AIR, FIRE and WATER
BECAUSE OF ARISTOTLE’S GREAT
INFLUENCE……
DEMOCRITUS’
ATOMS
...’ATOMS’ DIED FOR
ABOUT 1,400 YEARS
UNTIL...
IN THE
1700’S…
THE PREDOMINATE BELIEF BY THE MID
1700’S 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.
HOWEVER, THERE WAS CONTROVERSY
AS TO WHETHER ELEMENTS
ALWAYS COMBINE IN THE SAME
RATIO WHEN FORMING A
PARTICULAR COMPOUND.
IN THE 1790’S, 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.
ANTOINE LAVOISIER
Matter can be
neither created
nor destroyed!
HE BEGAN TO GATHER
EVIDENCE ABOUT HOW
MATTER BEHAVED
BEFORE AND AFTER A
REACTION.
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’.
JOHN DALTON INVESTIGATED
TWO OTHER FUNDAMENTAL
IDEAS
The Law of
Definite
Proportion
The Law
of Multiple
Proportions
LAW OF
DEFINITE
PROPORTIONS
LAW OF
MULTIPLE
PROPORTIONS
A CHEMICAL COMPOUND IS ALWAYS
COMPOSED OF THE SAME ELEMENTS IN THE
SAME PROPORTION BY MASS.
CARBON
MONOXIDE
+
C
=
O
CO
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.
CARBON
MONOXIDE
CARBON
DIOXIDE
+
C
O
+
+
C
=
O
CO
=
O
CO2
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:
1.ALL MATTER IS
COMPOSED OF EXTREMELY
SMALL PARTICLES CALLED
ATOMS
2.ATOMS OF A GIVEN
ELEMENT ARE IDENTICAL
IN SIZE, MASS, AND
OTHER PROPERTIES.
ATOMS OF DIFFERENT
ELEMENTS DIFFER IN
SIZE, MASS, & OTHER
PROPERTIES
ELEMENT
2
ELEMENT
3
ELEMENT
4
3.ATOMS CANNOT BE
SUBDIVIDED, CREATED,
OR DESTROYED.
4.ATOMS OF DIFFERENT
ELEMENTS COMBINE IN
SIMPLE WHOLE NUMBER
RATIOS TO FORM
CHEMICAL COMPOUNDS.
5.IN CHEMICAL
REACTIONS, ATOMS ARE
COMBINED, SEPARATED,
OR REARRANGED.
+
+
DALTON AND HIS
CONTEMPORARIES
THE EARLIEST THEORISTS
THOUGHT THE ATOM WAS
HARD AND ROUND,
MUCH LIKE TINY MARBLES
OR BALL BEARINGS.
ALTHOUGH DALTON THOUGHT ATOMS
WERE INDIVISIBLE, INVESTIGATORS
IN THE LATE 1800’S PROVED
OTHERWISE.
IT SOON BECAME CLEAR THAT ATOMS
ARE ACTUALLY COMPOSED OF SEVERAL
BASIC TYPES OF SMALLER PARTICLES.
AND IT’S THE NUMBERS AND
ARRANGEMENTS OF THESE SUBATOMIC PARTICLES THAT
DETERMINES THE IDENTITY OF THE
ATOM.
THE FIRST DISCOVERY OF A SUBATOMIC
PARTICLE RESULTED FROM THE
INVESTIGATIONS INTO THE RELATIONSHIP
BETWEEN ELECTRICITY AND MATTER.
IN THE LATE 1800’S, MANY EXPERIMENTS
WERE PERFORMED IN WHICH ELECTRIC
CURRENT WAS PASSED THROUGH VARIOUS
GASES AT LOW PRESSURE.
CARRIED OUT IN TUBES CALLED
CATHODE-RAY TUBES
J.J. THOMPSON
Around 1900
THOMPSON NOTICED THAT WHEN
CURRENT WAS PASSED THROUGH A
CATHODE RAY TUBE, THE SURFACE OF
THE TUBE DIRECTLY OPPOSITE THE
CATHODE GLOWED.
THOMPSON THEORIZED THAT THE
GLOW WAS CAUSED BY A STREAM OF
‘PARTICLES’.
HE CALLED THIS STREAM A
‘CATHODE RAY’.
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
THOMPSON’S 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’.
+
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.
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.
THOMPSON WAS ‘ENGLISH’………
HE CALLED HIS MODEL THE
‘PLUM PUDDING ATOM’
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 ATOM……HYDROGEN.
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 ELECTRON’S
MASS IS 9.109x10-31kg
THOMPSON’S & MILLIKAN’S IDEAS
ATOMS ARE IN FACT DIVISIBLE.
ELECTRONS ARE PRESENT IN ATOMS OF ALL
ELEMENTS.
ONE OF THE ATOM’S 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.
BUT, NO ONE KNEW WHAT THE
INSIDE OF AN ‘ATOM’ WAS
REALLY LIKE UNTIL……
ERNEST RUTHERFORD
What’s
inside an
atom?
IN 1911, RUTHERFORD
PERFORMED ONE OF THE
MOST BRILLIANT
EXPERIMENTS EVER.
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……
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!
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’.
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.
electron
e
-1
0
9.11x10-28
proton
+
p
+1
1
1.67x10-24
neutron
n0
0
1
1.67x10-24
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.
THE ELECTRONS SURROUND THE NUCLEUS
AND OCCUPY MOST OF THE ATOM’S 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
IT’S THE NUMBERS OF PROTONS IN AN ATOM
THAT MAKES ATOMS DIFFERENT.
AN OXYGEN ATOM HAS 8 PROTONS IN IT’S
NUCLEUS.
A HYDROGEN ATOM HAS 1 PROTON IN IT’S
NUCLEUS.
THE ‘ATOMIC NUMBER OF’ AN ELEMENT IS
THE NUMBER OF PROTONS IN THE NUCLEUS
OF AN ATOM OF THAT ELEMENT.
SINCE OXYGEN’S NUCLEUS HAS 8 PROTONS
IT’S ATOMIC NUMBER IS 8.
THE PROTONS IDENTIFY THE TYPE OF ATOM,
THE ONLY ATOM WITH 8 PROTONS IS
OXYGEN.
ATOMS OF THE FIRST TEN ELEMENTS
Hydrogen
Helium
Lithium
Beryllium
Boron
Carbon
Nitrogen
Oxygen
Fluorine
Neon
H
He
Li
Be
B
C
N
O
F
Ne
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
6
7
8
9
10
0
2
4
5
6
6
7
8
10
10
1
4
7
9
11
12
14
16
19
20
1
2
3
4
5
6
7
8
9
10
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
IT’S NUCLEUS AND DEPENDS ON THE
NUMBER OF PROTONS AND NEUTRONS.
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 ATOM’S
COMPOSITION.
THE COMPOSITION OF ANY ATOM CAN BE
REPRESENTED IN SHORTHAND NOTATION:
CHEMICAL COMPOSITION SHORTHAND
# OF PROTONS
+
# OF NEUTRONS
Cl
MASS
NUMBER
35
ATOMIC
NUMBER
17
NUMBER OF
PROTONS
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.
ISOTOPES ARE CHEMICALLY ALIKE BECAUSE
THEY HAVE IDENTICAL NUMBERS OF
PROTONS AND ELECTRONS.
IT’S THE ELECTRONS AND PROTONS THAT
ARE RESPONSIBLE FOR CHEMICAL
BEHAVIOR.
BERYLLIUM ISOTOPES
proton
neutron
electron
SODIUM ISOTOPES
EXAMPLE OF AN ISOTOPE
ATOMIC MASS
35
17
Cl
18
NEUTRONS
37
17
Cl
20 NEUTRONS
ATOMIC NUMBER
IONS
AN ELEMENT’S 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: IT’S THE PROTONS THAT DEFINE THE
TYPE OF ATOM IT IS, BUT THE
ELECTRONS DEFINE THE ATOM’S
CHARGE.
‘LOST’ AN
ELECTRON
= + CHARGE
‘GAINED’ AN
ELECTRON
= - CHARGE
SOME ATOMS
GAIN ELECTRONS
ATOM’S IONIC CHARGE =
NUMBER OF PROTONS – NUMBER OF ELECTRONS
-
-
-
-
-
-
-
O
-
-
-
-
-
-
O-2
-
ATOMS, IONS, AND ISOTOPES
ATOMS
NEUTRAL AND ARE DEFINED BY
THE # OF PROTONS IN THEIR
NUCLEUS
3 p+ = Li ATOM, ETC.
IONS
HAVE AN ELECTRICAL CHARGE
DETERMINED BY
# PROTONS - # ELECTRONS
N-2 = 7 p+ - 9 e- ; ETC.
ISOTOPES
TWO ATOMS WITH THE SAME #
OF PROTONS, BUT DIFFERENT
#’S OF NEUTRONS OR MASSES
CALCIUM-40 & CALCIUM-44
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 ATOM’S OUTER ORBIT.
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.
ATOMS WITH ‘FILLED’ SHELLS ARE
STABLE, OR NON-REACTIVE.
THESE
ARE CALLED ‘INERT GASES’