History of the atom

From Democritus to Fukashima, people and discoveries along the way

1. The Atom and its History

2. Democritus (465
BC)
•Ancient Greeks came to
believe all matter consisted of differing
amounts of only 4 basic substances: earth,
fire, water, and ether
•Leucippus, teacher of Democritus, proposed
matter was made of small particles
•D. was first to use the word atomos:
the smallest, indivisible part of matter

3. Back in the Iron Age….
•Some elements are found in nature in a
relatively pure form.
•Sulfur, copper, gold,
silver, and iron were
made into decorative
and useful objects.

4. The Alchemists (Dark Ages till
the Renaissance)
•Looked for the
philosophers stone
•thought they would
find a way to turn Pb
into Au
•Newton dabbled in
alchemy

5. The modern age begins
•Henning Brand of Germany discovered
phosphorus in 1669.
• He collected 50
buckets of urine,
fermented it, and
then boiled off the
water.

6. Joseph Priestley
•Discovers oxygen -1774
(at the same time as
Lavoisier & Scheel)
A “natural philosopher”
Also credited with
inventing soda water!
(1733-1804)

7. Antoine Lavoisier
•Law of conservation of
mass
•Discovers nitrogen gas,
and that oxygen can be
chemically separated
from certain compounds
•confirms law of definite
proportions
•father of modern
chemistry
•loses his head to the
French Revolution
1743-1794

8. John Dalton
•Father of modern
Atomic Theory
•thought atoms of an
element were all
identical and
indivisible
•compounds are formed
from atoms of
different elements
1766-1844

9. Dalton’s model

10. William Prout
•Law of Definite
Proportions
1785-1850, a physician
Distilled HCl acid from
stomach juices, and
suggested that H is the
fundamental particle

11. Dimitri Mendeleev (1834-1907)
•Organizes the first
periodic table
•columns based on
valence (reactivity)
•position in a row
based (mostly ) on
atomic weight
•left places in table for
elements which were
not yet discovered

12. Mendeleev’s original table

13. Chemistry and Physics Join
Forces
The late 19th century through the 20thcentury

14. J J Thomson
•Discovers the electron
•Plum Pudding Model
of the atom….
•All the charged
particles were
randomly scattered
like “plums in
pudding”
•did not know about
neutrons
•Nobel Prize 1906.
Thompson's experiment to discover electrons (1897)
1856-1940

15. Thomson’s model

16. Wilhelm Roentgen
1845-1923
Discovered X-rays in 1895:
his wife’s hand

17. Becquerel
(1852-1908)
In 1896, Henri Becquerel discovered that
uranium salts emitted rays that resembled
X-rays in their penetrating power. He
demonstrated that this radiation, unlike
phosphorescence, did not depend on an
external source of energy, but seemed to
arise spontaneously from uranium itself.
Becquerel had, in fact, discovered
radioactivity.

18. The Curies
Pierre Marie
Marie (1867-1934) - first woman to win a Nobel Prize
Pierre (1859-1906) – died in traffic accident
Formulated the theory of radioactivity while working
with uranium; also discovered Polonium (named after
Poland) and radium
She was a pioneer in using radiation in medicine, but was
unaware of the hazards of radiation.

19. Nikola Tesla
1856-1943
•Investigated X-rays
•Got skin damage while
experimenting

21. Ernest Rutherford (1871-1937)
•Electrons are separated
from the nucleus
•nucleus has positive
charge and the shells are
negative
•atoms are mostly empty
space (1911) - the
Gold foil experiment
•Planetary model

22. Rutherford’s “planetary” model

23. Henry Mosley (1887-1915)
•Discovers the atomic
number
•corrects Mendeleev’s
periodic table, basing
it on Atomic Number
•dead in his 20’s
….WWI

24. +1
+2
+3
Los Alamos National Lab

25. Relationships on the Periodic
Table

26. Max Planck
the energy of an
orbiting electron is
determined by the
frequency of its wave
1858-1947
Father of Quantum Theory

27. Neils Bohr (1885 - 1962)
•Electrons are found at
distinct distances from
the nucleus
•wave model
•cloud model
•quantum mechanics

28. Bohr’s energy level model

29. Erwin Schrödinger
•With Heisenberg,
calculated probable
locations of electrons
•Quantum mechanics
and Schrödinger ’s cat
1887-1961

30. Louis de Broglie
•Electrons orbiting the
nucleus exhibit wave
properties
•Moving matter has a
wavelength related to
its momentum
•Leads to development
of the cloud model of
the atom
1892-1987

31. Electron cloud model
Comparison of the two models

32. The 1927 Solvay Conference

33. Werner Heisenberg
•Mathematical models
with Schrodinger
•The Uncertainty
Principle
•you can not know both
the position and speed
of an electron
simultaneously
1901-1976

34. Heisenberg was a hydrogen filled nazi zeppelin that came to this
disastrous end in the 1930’s.

35. Werner Heisenberg was a German physicist who, in his late
twenties, introduced what is known as the Heisenberg
Uncertainty Principle. This discovery shook the very
foundation of subatomic physics.

36. Heisenberg’s principle states:
For any moment in time, it is
impossible to know the position and
the momentum of a moving particle.
Simply because the act of observing affects the behavior of the observed.

37. I’m sure you’re aware of some things that change their behavior
depending on how they are being observed, for example:

40. In the case of particles, the observer also affects the behavior of
the observed. There are limits to how much we can know about a
particle at any given moment. Take this picture for example:
However, if we moved the magnifying glass,
Right now we can see the left side clearly.

41. Now we can see the right side clearly but can no longer see the left.

42. Imagine this:
A microscope that can see electrons in orbit around the nucleus
We shoot ordinary light waves at the electron to find its
position,
We try gamma rays (shorter wavelength).
The problem with this is that gamma rays have so much
energy (high frequency), that upon contact, the electron
is knocked out of orbit making impossible to know its
momentum.
but the wavelength is too long to be obstructed by
the electron,so...

43. Albert Einstein
1879-1955
•A “slow student” who revolutionized
science and the world
•Mass is a form of energy!

E = mc
2

44. Einstein didn’t like Quantum
Mechanics
•Einstein to Bohr, “God
does not play dice
with the universe”
•Bohr, in response,
“Who are you to be
telling God what to
do?”

45. Paul Dirac
Further developed quantum theory
from work of
Heisenberg and Schrodinger
Shared a Nobel Prize - 1933
Worked on Uranium
enrichment during WW II

46. James Chadwick
•1932 discovers the
neutron
•Explains isotopes
http://www.nobel.se/physics/laureates/1935/chadwick-bio.html
1891-1974

47. Lise Meitner
•Realized that some
weight was lost during
nuclear fission: E=mc
2
•Was part of the team
that discovered
nuclear fission in late
1930s
1878-1968

48. Enrico Fermi
(1901-1954)
•Emigrated from Fascist Italy in 1938 after
winning Nobel Prize
•Built first nuclear reactor – underneath the
stadium at the University of Chicago - 1942

49. Arthur Compton
Worked with Fermi on first reactor
Demonstrated the particle aspect of
electro-magnetic radiation:
The Compton Scattering Effect
1892-1962

50. Glenn T. Seaborg
1912-1999
•Responsible for the
Actinide concept
•Discovered ten elements:
plutonium, americium,
curium, berkelium,
californium, einsteinium,
fermium, mendelevium,
nobelium, and 106 (named
after him)

51. Radioactivity
Three types
•Alpha α – a He nucleus (2p+2n)
•Beta β – an electron
•Gamma γ – pure energy: EM waves

52. Penetration of Matter
•Though the most massive and most energetic of
radioactive emissions, the alpha particle is the
shortest in range because of its strong interaction
with matter. The electromagnetic gamma ray is
extremely penetrating, even penetrating
considerable thicknesses of concrete. The electron
of beta radioactivity strongly interacts with matter
and has a short range.