Atomic Structure

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Atomic Structure Scientists

• "Understanding means seeing that the same thing
  said different ways is the same thing." ---
  Ludwig Wittgenstein

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Democritus of Abdera

• "Laughing Philosopher in the 4th century B.C.
• Master Leucippus of Miletus Democritus
  originated the atom concept.
• There are five major points to their atomic idea.

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Democritus Atomic Ideas

• Point 1 - All matter is composed of atoms, which
  are bits of matter too small to be seen. These
  atoms CANNOT be further split into smaller
  portions.
• Point 2 - There is a void, which is empty space
  between atoms.
• Point 3 - Atoms are completely solid.
• Point 4 - Atoms are homogeneous, with no
  internal structure.
• Point 5 - Atoms are different in their size,
  shape, weight.
• Greeks thought he was crazy!!!! Democritus knew
  that atoms were indestructible units of matter,
  but he could not explain atoms chemical behavior.

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John Dalton ( 1766-1844)

• The Father of the Chemical Atomic Theory
• Teacher at the age of 12 years old
• He wanted to expand upon Democritus theory
• Dalton created several hypotheses performed
  experiments
• Created published Daltons Atomic Theory

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Daltons Atomic Theory

• Matter is composed of small indivisible particles
  called atoms. The atom is the smallest unit of an
  element that enters into chemical combination.
• An element is composed entirely of one type of
  atom. The properties of all the atoms of one
  element are identical and are different from
  those of any other element.
• A compound contains atoms of two or more
  different elements. The relative number of atoms
  of each element in a particular compound is
  always the same. LAW OF DEFINITE PROPORTIONS
• Atoms do no change their identities in chemical
  reactions. Chemical reactions simply change the
  way the atoms are joined together.

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Daltons Atomic Model

• There it is! Dalton created this model in 1807.
• Indivisible Spheres that are involved in chemical
  reactions.

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Sir Joseph John Thomson

• 1856-1940
• The man who chipped into the atom
• On April 30, 1897 announced that cathode rays
  were negatively charged particles which he called
  'corpuscles.'
• "At first there were very few who believed in the
  existence of these bodies smaller than atoms. I
  was even told long afterwards by a distinguished
  physicist who had been present at my 1897
  lecture at the Royal Institution that he thought
  I had been pulling their legs.' "
• Corpuscles are now called electrons

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J.J. Thomson
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Cathode Ray Tube

• The two plates about midway in the CRT were
  connected to a powerful electric battery thereby
  creating a strong electrical field through which
  the cathode rays passed. Thomson also could use
  magnets, which were placed on either side of the
  straight portion of the tube just to the right of
  the electrical plates. This allowed him to use
  either electrical or magnetic or a combination of
  both to cause the cathode ray to bend.

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Plum Pudding Atomic Model

• 1904 article We suppose that the atom consists
  of a number of corpuscles moving about in a
  sphere of uniform positive electrification .
• Plum Pudding model," where the pudding
  represents the sphere of positive electricity and
  the bits of plum scattered in the pudding are the
  electrons.

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Eugen Goldstein (1850-1930)

• 1886, the German scientist observed "canal rays"
  flowing in the opposite direction  through a
  cathode ray tube by putting holes or canals in
  the cathode. 
• From this discovery the idea was built that there
  is a unit of positive charge in the atom referred
  to later as the proton. 
• Why dont I have a picture? Cant find one!!!
  Who stole his thunder?

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Ernest Rutherford (1871-1937)

• The New Zealand radioactive scientist
• Worked with Sir J.J. Thomson
• He was fun, outgoing and vigorous, the life of
  the party -- a great, big, over-grown child. He
  was also a hard-working scientist who loved
  science for itself and never tired of playing in
  the laboratory.

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Gold Foil Experiment
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Rutherfords Accomplishments

• For the purposes of his 1911 paper, he considered
  the nucleus to act as a point
• "We shall suppose that for distances less that
  1012 cm the central charge and also the charge
  on the alpha particle may be supposed to be
  concentrated at a point." Rutherford never used
  the word "nucleus" in his paper. His phrase was
  "charge concentration.
• We connect him with the discovery of the nucleus
• He furthered concluded that atom is primarily
  empty space with a negative region surrounding
  the dense core.
• Renamed canal rays to protons in 1920 after his
  work with the nucleus.

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Sir James Chadwick (1891-1974)

• Accidentally found himself in the line for those
  hoping to major in physics.
• Trapped in Germany when WW I broke out, Chadwick
  was imprisoned in a horse stall at a racetrack
  that served as an internment camp
• Worked with Rutherford
• In 1932, Chadwick made a fundamental discovery in
  the domain of nuclear science he proved the
  existence of neutrons

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Sir James Chadwick

• All elements except hydrogen contain neutrons
• Chadwick paved the way towards the fission of
  uranium 235 and towards the creation of the
  atomic bomb.
• Time Magazine declared the discovery of the
  neutron as one of the 100 Most Important
  Milestones of the 20th century.
• Helped with the Nuclear Atomic Model

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Nuclear Atomic Model
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Robert Millikan (1868-1953)

• Taught himself physics!
• In 1909, he began experiments to determine the
  electric charge of a single electron in Chicago.
• In 1916, he proved Einsteins theory of the
  photoelectric effect.

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Oil Drop Experiment

• Determined the mass and charge of the electron
• Charge 1.60 x10-19 C
• Mass 9.11 x10-28 g

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Subatomic Particle Summary
Particle Symbol Electrical Charge Actual Mass When Discovered
PROTON p 1 1.67 x10-24 g 1886
ELECTRON e- -1 9.11 x10-28 g 1897
NEUTRON n 0 1.67 x10-24 g 1932
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Nobel Prize Winners

• Sir J.J. Thomson (1906)
• Ernest Rutherford (1908)
• Robert Millikan (1923)
• Sir James Chadwick (1935)