The document traces the development of atomic theory from ancient Greek philosophers to modern scientists. It describes the early atomic models of Democritus, Aristotle, Dalton, Thomson, and Rutherford, and how each built upon the work of previous scientists. Later models such as those proposed by Bohr, Schrodinger, and Heisenberg incorporated the ideas of discrete energy levels and electron clouds rather than fixed orbits, bringing atomic theory closer to its current form.

1. The Atom
Notes

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

3. The Ancients
Democritus
Aristotle

4. Democritus

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

7. Aristotle

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

9. The Moderns
Dalton
Thomson
Rutherford
Bohr
Schrodinger & Heisenberg

10. Dalton

11. Dalton’s Model of the Atom
Created the 1st Atomic Theory
His theory explained why the
elements in a compound always
bond in the same way

12. Dalton’s Model of the Atom
He proposed the theory:
All matter is made up of individual
particles, called atoms, which
cannot be divided.

13. Dalton’s Model of the Atom
All elements are composed of
same atoms

14. Dalton’s Model of the Atom
All atoms of the same element
have the same mass

15. Dalton’s Model of the Atom
Atoms of different elements
have different masses.

16. Dalton’s Model of the Atom
Compounds contain atoms of
more than one element.

17. Dalton’s Model of the Atom
In a particular
compound, atoms of different
elements always combine in
the same way

18. The Dalton Model

19. The Dalton Model
 Video:
 http://www.youtube.com/watch?v=HFF-
2wyyTKc&feature=results_video&playnext
=1&list=PLF3AEE12BDB1E3858

20. J. J. Thomson

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

25. The Thomson Model
 Video:
 http://www.youtube.com/watch?v=JwdGFZ
A3WOs

26. Rutherford

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°.

29. Rutherford’s Model of the
Atom
Proved most of an atom is
actually empty space!

30. Rutherford’s Model of the
Atom
The positive charge of an atom
must be concentrated in a very
small central area that he called
the nucleus.

31. Rutherford’s Model of the
Atom
Further experiments determined
that the positive charge of an
atom is by the number of
protons in the nucleus.

32. Rutherford’s Model of the
Atom
Each proton has a charge of +1.

33. The Rutherford Model

34. Rutherford’s Model of the
Atom and Gold Foil Test

35. Rutherford’s Model
 Video
 Nucleus of an Atom

36. Niels Bohr

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

42. The Bohr Model

43. Schrodinger &
Heisenberg

44. Schrodinger & Heisenberg
These scientists discovered that
electrons are less predictable
than in Bohr’s model of fixed
orbits.

45. Schrodinger & Heisenberg
Atoms gain or lose energy.
when electrons move from one
energy level to another

46. Schrodinger & Heisenberg
They use an electron cloud
model to show the most likely
locations for electrons as they
move around the nucleus.

47. Schrodinger & Heisenberg
The electron cloud represents
all the orbitals in an atom.

48. Schrodinger & Heisenberg
An orbital is a region of space
around the nucleus where an
electron is likely to be found.

49. Schrodinger & Heisenberg
Orbitals come in different
sizes, shapes, and locations

50. Schrodinger & Heisenberg
An electron configuration is the
arrangement of electrons in the
orbitals of an atom.

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

53. The Electron Cloud Model

54. The Electron Cloud Model
 Video:
 electron cloud model

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

61. The Nature of Science
 .