Quantum Theory,
Part 1
Development of the Atom
History
400 B.C. LEUCIPPOS and DEMOCRITUS
– Greek Philosophers
– Everything that is tangible (able to be touched) is made
of atoms, everything else is empty space.
– Matter can be broken down into atoms, which are the
smallest particles of matter. “ATOMOS”
– Solid and Indestructable
– Different materials are made up of different types and
mixtures of atoms.
– Different sizes and shapes of atoms lead to different
properties.
– NO EXPERIMENTAL EVIDENCE
“To understand the very large,
we must understand the very small.”
Democritus
DEMOCRITUS (400 BC) – First Atomic Hypothesis
Atomos: Greek for “uncuttable”. Chop up a piece of matter until you reach the atomos.
Properties of atoms:
• indestructible.
• changeable, however, into different forms.
• an infinite number of kinds so there are an infinite number of elements.
• hard substances have rough, prickly atoms that stick together.
• liquids have round, smooth atoms that slide over one another.
• smell is caused by atoms interacting with the nose – rough atoms hurt.
• sleep is caused by atoms escaping the brain.
• death – too many escaped or didn’t return.
• the heart is the center of anger.
• the brain is the center of thought.
• the liver is the seat of desire.
“Nothing exists but atoms and space, all else is opinion”.
History of the Atom
• Looked at beach
– Made of sand
• Cut sand
– Smaller sand
• Smallest possible
piece?
– Yes!!!!
– “Atomos” indivisible
Some Early Ideas on Matter
Empedocles
(Greek, born in Sicily, 490 B.C.)
–Suggested there were only four basic seeds
– earth, air, fire, and water.
–The elementary substances (atoms to us) combined in
various ways to make everything.
Aristotle
(Greek, born 384 B.C.)
–Added the idea of “qualities”
– heat, cold, dryness, moisture – as basic elements which
combined as shown in the diagram (previous page).
–Hot + dry made fire; hot + wet made air, and so on.
History
Aristotle (prized pupil of Plato)
– Greek Philosopher
– Matter is made of a continuous substance
called “hyle”
– Matter can be infinitesimally broken down.
There is no such thing as a smallest particle.
– 4 elements make up all substances.
» Fire - hot
» Air - light
» Earth - cool, heavy
» Water - wet
» Blend these in different proportions to get all
substances
– NO EXPERIMENTAL EVIDENCE
Who Was Right?
• Greek society was slave
based.
• Beneath the “Famous” to work
with hands.
– Thus, they did not
experiment.
• Greeks settled disagreements
by argument.
• Aristotle was more famous.
• He won.
• His ideas carried through until
the 17th century.
Followed by the onset of alchemy
and The Sceptical Chymist
Transmutation: changing
one substance into another
Modern Chemistry
• Beginnings of modern chemistry
were seen in the 16th and 17th
centuries, where great
advances were made in
metallurgy, the extraction of
metals from ores.
• In the 17th century, Boyle
described the relationship
between the pressure and
volume of air and defined an
element as a substance that
cannot be broken down into two
or more simpler substances by
chemical means.
Early Ideas on Elements
Robert Boyle stated...
– Air therefore could not
be an element because
it could be broken down
into many pure
substances.
Robert Boyle
Laws
1782 Antoine Lavoisier
– French
Law of Conservation of Mass (Matter)
– Matter can not be created nor
destroyed.
– Translation: In ordinary chemical
reactions, the total mass of the
reactants is equal to the total
mass of the products.
– First Experimental evidence:
Mass of Sn + Mass of O = Mass of Sn and O
Conservation of Mass
Before reaction
High
voltage
electrodes
After reaction
O2
glass
chamber
High
voltage
H2O
O2
H2
5.0 g H2
80. g O2
+ 300. g (mass of chamber)
385 g total
0. g H2
45
? g H22O
40. g O2
+ 300. g (mass of chamber)
385 g total
Law of Conservation of Matter
Pb – soft, grayish metal
S – pale yellow solid
PbS – lustrous, black solid
+
1.56 g of
sulfur
10.00 g of lead
11.56 g of
lead sulfide
+
10.00 g of lead
+
3.00 g of
sulfur
11.56 g of
lead sulfide
1.44 g of sulfur
(leftovers)
Modern Chemistry
1799 Joseph Louis Proust
– French
Law of Definite Proportions (Constant Composition)
– Each compound has a specific ratio of elements
» Translation: Compounds have an unchanging chemical
formula.
– It is a ratio (proportion) by mass
– This holds true regardless of the origin, how it was obtained, or
how large a sample.
» Water is always 8 grams of oxygen for every one gram of
hydrogen (8:1)
» NaCl is table salt. It is always 1.54 g Cl (chlorine) for every
1.0 g Na (sodium).
Law of Definite Proportions
Law of Definite Proportions
Pb – soft, grayish metal
S – pale yellow solid
PbS – lustrous, black
solid
+
1.56 g of
sulfur
10.00 g of lead
11.56 g of
lead sulfide
+
+
3.00 g of
sulfur
10.00 g of lead
11.56 g of
lead sulfide
+
18 g of lead
1.44 g of sulfur
(leftovers)
+
1.56 g of
sulfur
11.56 g of
lead sulfide
8.00 g of lead
(leftovers)
Dalton’s Atomic Theory
1803 John Dalton
English School Teacher
–
–
1)
2)
3)
4)
Created the first logical hypothesis about the existence of
atoms.
This was called his ATOMIC THEORY.
All matter is composed of small particles called atoms, that
are indivisible and indestructible.
Atoms of each element are identical. In particular, they have
the same mass and properties. Atoms of different elements
are different. They have different masses and properties.
Chemical changes involve the combination, separation, or
rearrangement of atoms. Atoms are not created, destroyed,
divided into parts, or converted into other kinds of atoms.
Compounds are formed when atoms combine. Each
compound has a specific number and kinds of atom. They
are combined in definite whole-number ratios.
Dalton’s Model of the Atom
Dalton’s Law of Multiple Proportions
• Dalton could not use his theory to determine the
elemental compositions of chemical compounds
because he had no reliable scale of atomic masses.
• Dalton’s data led to a general statement known as the
law of multiple proportions.
• Law states that when two elements form a series of
compounds, the ratios of the masses of the second
element that are present per gram of the first element
can almost always be expressed as the ratios of
integers.
Law of Multiple Proportions
John Dalton (1766 – 1844)
If two elements form more than one
compound, the ratio of the second
element that combines with 1 gram of the O:H O:H
first element in each is a simple whole
16:2 32:2
number.
= 8:1
Two substances are decomposed and
determined to be made of both oxygen
and hydrogen. When the masses of the
elements are analyzed, it is found out the
= 16:1
What?
• Water is 8 grams of oxygen per gram of
hydrogen.
• Hydrogen peroxide is 16 grams of oxygen
per gram of hydrogen.
• 16 g to 8 g is a 2:1 ratio
• True, because you have to add a whole
atom, you can’t add a piece of an atom.
Law of Multiple Proportions
What are the masses of the compounds?
Law of
Conservation
of Matter
Law of
Conservation
of Matter
1.3333
Law of
Conservation
of Matter
2.6667
Law of
Conservation
of Matter
Law of Multiple Proportions
According to the
Law of Definite
Proportions these
two substances
are different
According to the
Law of Definite
Proportions these
two substances
are different
1.3333
What does this tell us?
2.6667
Law of Multiple Proportions
1.3333
2.6667
What could their formulae be?
What makes them different?
The second compound has twice as much O as the first
Proof
• Mercury has two oxides. One is 96.2 % mercury by
mass, the other is 92.6 % mercury by mass.
For every 100. grams of substance
A:
96.2 g Hg
3.8 g O
B:
92.6 g Hg
7.4 g O
• Show that these compounds follow the Laws of Conservation of
Matter, Definite Proportions, and Multiple Proportions.
• How much oxygen must there be?
WHY?
!?!?
Proof
What is the
significance
of these
values?
Ratio of Hg:O
96.2 g Hg
92.6 g Hg
3.8 g O
7.4 g O
= 25.315789 g Hg / g O
= 12.513513 g Hg / g O
25.315789 / 12.513513
= 2.02 = 2.0
What
does
this
mean?
Substance A has 2x as much Hg to O as Substance B
• Speculate on the formula of the two oxides.
If Substance B = HgO then Substance A = Hg2O
Avogadro’s Hypothesis
Gay-Lussac
– French
• Attempted to establish the formulas of chemical
compounds by measuring, under constant
temperature and pressure conditions, the
volumes of gases that reacted to make a given
chemical compound, together with the volumes
of the products if they were gases.
– Compounds always react in whole number ratios by
volume.
Gay-Lussac
Avogadro
– Italian
• Gay-Lussac’s results were explained by
Avogadro’s hypothesis, which proposed that
equal volumes of different gases contain equal
numbers of gas particles when measured at the
same temperature and pressure.
Avogadro
History
1833 Michael Faraday
– British
– Proved that electricity is made of fundamental
particles.
1886 Eugene Goldstein
– English



Used Crooke’s tube (cathode ray tube) to study
canal rays.
These rays were oppositely charged cathode rays.
Credited with the discovery of the proton.
Goldstein’s Experiment
Voltage source
Metal
+
Cathode
Anode
Cathode Ray Tube
Goldstein’s Experiment
Voltage source
-
-
+
Cathode Rays
Goldstein’s Experiment
Voltage source
-
-
+
Cathode Rays
•Attracted to positively charged Anode,
these rays must be negatively charged.
Goldstein’s Experiment
Voltage source
-
-
+
Goldstein’s Experiment
Voltage source
-
Canal Rays
-
+
Attracted to negatively charged
plate, hence they must be positively
charged.
1895 Wilhelm Conrad Röntgen
– German




Discovered X-rays by accident
Covered the Lenard tube with lightproof paper and projected the
cathode rays onto various objects.
Piece of fluorescent material glowed under exposure to the
cathode rays.
 Moving the fluorescent material further and further away from
the Lenard tube -- glowed up to 2 meters away.
Röntgen knew that the cathode rays could not penetrate the
lightproof covering over the Lenard tube
 Hypothesized that the glowing of the fluorescent material
must be the result of some new kind of radiation.
 He began experimenting with putting different materials and
objects between the Lenard tube and the fluorescent material
and observing how the radiation passed through them.

His wife put her hand in the path of the cathode ray.
 The shadows from his wife’s hand over a photographic
plate clearly showed the bones inside her hand and her
wedding ring, while her flesh became transparent.
 Röntgen named his discovery X-rays because of their
unknown properties.
1896 Henri Becquerel
– French





Discovered radioactivity by accident
Fascinated by the strange ghostly images and the mysterious
emanations produced from Röntgen's X-rays.
Both he and his father had studied the phenomenon of
phosphorescence .
 When exposed to sunlight, material gives off light.
 Laboratory filled with lumps of stone and wood that
shone in the dark.
He thought immediately of putting some phosphorescent rock on
photographic paper to see if it would darken it in the same way
as one of Röntgen's X-ray sources.
He exposed the material to sunlight and placed it on
photographic plates wrapped in black paper.
 When developed, the plates revealed an image of the
uranium crystals.

Becquerel concluded "that the phosphorescent
substance in question emits radiation which
penetrates paper opaque to light."
 Initially he believed that the sun's energy was
being absorbed by the uranium which then
emitted X rays.
 Further investigation was delayed because
the skies over Paris were overcast and the
uranium-covered plates Becquerel
intended to expose to the sun were
returned to a drawer.
 As a check, he then developed the
photographic plate and found that the
fogging had again occurred, even though
the uranium salt could not have
phosphoresced since it had been in
darkness for some days. This meant that
the uranium emitted radiation without an
external source of energy such as the sun.
To see whether the effect depended on the uranium
salts having previously been exposed to sunlight at all,
Becquerel next prepared the salts in darkness.
 He also performed the experiment in darkness, but
found the same result – the fogging of the photographic
plate did not depend on phosphorescence.
 After further work, his newly discovered rays could
pass through metal plates and still fog the
photographic plate, though less intensely.
Becquerel had discovered radioactivity, the spontaneous emission of
radiation by a material.
 "There is an emission of rays without apparent cause. The sun
has been excluded."
 The phenomenon was found to be common to all the uranium salts
studied and was concluded to be a property of the uranium atom.
Rays emitted by uranium caused gases to ionize
 They differed from X-rays in that they could be deflected by electric
or magnetic fields.
 Must be charged particles.



Maltese Cross
Anyone for a Curie




Somehow, the uranium was able to give off rays
of energy spontaneously.
He suspected some unknown element in uranium
ore to be the cause.
Becquerel hired Marie Curie as an assistant to
isolate this unknown element which
spontaneously gave off high amounts of energy.
With her husband Pierre, Madame Curie took
Pitchblende, which contained the radioactive
element Uranium by the ton and carefully isolated
the radioactive components over several years.
 What they found was that there were more
than one radioactive element in it because
they found an element that was far more
radioactive than the element uranium.

The Curies isolated a new chemical element which
spontaneously emitted energy. They named it
Polonium after their native country.

Four years later, the Curies isolated another substance
that released lots of energy. This new element was called
radium. The Curies coined the terms “radiation” and
“radioactivity.”