2. The Atom
From the Greek prefix A- meaning
“not”
And the Greek Root –tomos meaning
“cut”
Means “uncuttable”
The ancient Greeks wanted to learn about
the smallest particle of matter
5. Democritus
Believed that all matter consisted of
extremely small particles that could not
be divided.
He called these particles atoms (from
the Greek “ατοµος”, meaning “uncut” or
“indivisible”).
6. Democritus
He believed there were different types of
atoms with specific sets of properties.
The atoms in liquids, for example, were
round and smooth
The atoms in solids were rough and prickly
8. Aristotle
He did not think there was a limit to the
number of times matter could be divided
He thought that all substances were built
up from only four elements
Earth
Air
Fire
Water
21. J. J. Thomson’s Model of
the Atom
Thomson’s experiments with
beams of charged particles in a
sealed glass tube led him to the
conclusion that atoms were
made of even smaller particles
22. J. J. Thomson’s Model of the
Atom
Thomson reasoned:
If the charge of an atom is
neutral, the atom must contain
equal amounts of both positive
and negative charges
23. The Thomson Model
Thomson said that
negative charges
were evenly
scattered throughout
an atom filled with a
positively charged
mass of matter.
24. The Thomson Model
Called the
“Plum Pudding
Model” after a
popular dessert
of the time
27. Rutherford’s Model of the
Atom
Rutherford discovered that
uranium emits fast-moving
particles with a positive charge.
He called them alpha particles.
28. Rutherford’s Model of the
Atom
In an experiment he charted the
path of alpha particles after they
passed through a thin layer of
gold foil and a number of the
particles were deflected.
Many more than
expected, sometimes by more
than 90°.
37. The Bohr Model of the
Atom
In Bohr’s model, electrons
move with constant speed in
fixed orbits around the
nucleus, like planets around a
sun.
38. The Bohr Model of the Atom
Electrons gain or lose energy
when they move between orbits
or energy levels. Energy levels
are like stairs on a staircase or
shelves in a bookshelf
39. The Bohr Model of the Atom
Evidence for discrete, unique
energy levels comes from the
light given off when energy is
added to the atoms of an
element (such as when
fireworks explode or electricity
is added to a neon light).
40. The Bohr Model of the Atom
No two elements have the
same set of energy levels, so
the emission pattern can be
used to identify the element.
41. The Bohr Model of the Atom
Video”
The Niels Bohr Rap
51. Schrodinger & Heisenberg
The most stable electron
configuration is the one in which
the electrons are in orbitals with
the lowest possible energies
52. Video :
Change of Atom-Dalton, Thomson,
Rutherford, Bohr
55. The Nature of Science
Each scientist was correct for his
time and ability to make
observations.
As improvements in technology
came about, each later scientist
proved the previous scientist(s)
slightly incorrect.
56. The Nature of Science
Now there is a totally different
model of the atom from the first
model presented by Dalton.
Only some of the theories of each
scientist remain.
In general…
57. The Nature of Science
As the ability to
make better
observations
improves, the new
knowledge may
support or disprove
what we have held
to be true.
58. The Nature of Science
As the ability to make better
scientific observations improved,
Atomic theory changed over time
Scientists improved upon
previous scientists theories by
proving the correct and disproving
the incorrect
59. The Nature of Science
From Dalton’s solid sphere that
bonded the same way all the
time…
To Thomson’s “Plum Pudding “
model of equal amounts of
positive and negative charges…
60. The Nature of Science
Then Rutherford proved that the
equal charges were separated by
vast space in a nucleus and
orbiting electrons
And Bohr gave order to the
orbiting electrons saying that they
maintained constant orbits