Chapter 3 Historical Development of Atom

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Chapter 3Historical Development of Atom
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MCAS Learning Standards (2006)

• 2. Atomic Structure and Nuclear Chemistry
• Broad Concept Atomic models are used to explain
  atoms and help us understand the interaction of
  elements and compounds observed on a macroscopic
  scale. Nuclear chemistry deals with
  radioactivity, nuclear processes, and nuclear
  properties. Nuclear reactions produce tremendous
  amounts of energy and the formation of the
  elements.

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MCAS Learning Standards (2006)

• Recognize discoveries from Dalton (atomic
  theory), Thomson (the electron), Rutherford (the
  nucleus), and Bohr (planetary model of atom) and
  understand how these discoveries lead to the
  modern theory.
• Describe Rutherfords gold foil experiment that
  led to the discovery of the nuclear atom.
  Identify the major components (protons, neutrons,
  and electrons) of the nuclear atom and explain
  how they interact.
• Interpret and apply the laws of conservation of
  mass, constant composition (definite
  proportions), and multiple proportions.
• Write the electron configurations for the first
  twenty elements of the periodic table.

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MCAS Learning Standards (2006)

• Identify the three main types of radioactive
  decay (alpha, beta, and gamma) and compare their
  properties (composition, mass, charge, and
  penetrating power).
• Describe the process of radioactive decay by
  using nuclear equations and explain the concept
  of half-life for an isotope, for example, C-14 is
  a powerful tool in determining the age of
  objects.
• Compare and contrast nuclear fission and nuclear
  fusion.

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History of the Atom
Not the history of the atom itself, but the
history of the idea of the atom.
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Atom Definition

• Atom

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Democritus

• Greek Philosopher
• 450 BC
• Thought atoms were
• Used logic to formulate ideas
• One of the first to develop idea of atoms

http//images.search.yahoo.com/search/images/
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Contributing Principles to Idea of Atom

• Law of
• Antoine and Marie Lavoisier
• Conducted
• Late 1700s

http//images.search.yahoo.com/search/images/
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Contributing Principles to Idea of Atom

• Law of
• A given compound
• Joseph Louis Proust
• 1799

http//images.search.yahoo.com/search/images/
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Contributing Principles to Idea of Atom

• Law of Multiple Proportions
• If two elements A and B combine to form more than
  one compound,
• Real world examples
• water H2O
• Hydrogen Peroxide H2O2

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John Daltons Atomic Theory (1803)

• Elements composed of small particles called atoms
• All atoms of a given element are the same, but
  different from other elements

www.english.upenn.edu/jlynch/Frank/People/dalton.
html - 2k
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Studdy Buddy Review

• Describe the contribution of each towards the
  historical development of the atom
• Lavoisier
• Proust
• Democritus
• Dalton

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What is inside the atom?
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J.J. Thompson (1897)

• Cathode Ray Tube Experiments
• Conclusions
• Stream of
• Named
• Atoms are
• Found ratio
• (electrical charge of electron)
• (mass of electron)
• 1.76 x 108 coulombs 1 gram of electrons

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Thomsons Experiment

-

• Passing an electric current makes a beam appear
  to move from the negative to the positive end

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Thomsons Experiment

-

• By adding an electric field he found that the
  moving pieces were negative

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Robert Millikan (1909)

• Oil Drop Experiment
• Measured
• Charge of one electron
• -1.6x10-19C
• THUS.
• Mass of e-
• 9.11x10-28g

http//webphysics.davidson.edu/Alumni/ToHaynie/Oil
Drop/oilappa.htm
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Rutherfords experiment

• English physicist Ernest Rutherford (1911)
• Shot alpha particles at
• alpha particles
• A form of radioactivity
• When an alpha particle hits a fluorescent screen,
  it glows.

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Fluorescent Screen
Lead block
Uranium
Gold Foil
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He Expected

• The alpha particles to pass through without
  changing direction very much.

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What he expected
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He thought the mass was evenly distributed in the
atom
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What he got
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How Rutherford explained results

• Atom is mostly empty space.
• Small dense, positive piece at center. (NUCLEUS)
• Alpha particles are deflected by it if they get
  close enough.

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A little fun
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Credit for subatomic particles

• 1897 Thomson discovered the _________
• Used cathode ray tube
• (1918) Rutherford named
• Goldstein (1886) first discovered positively
  charged particle using cathode-ray tube with
  perforated cathode
• (1932) James Chadwick discovers ________
• Worked with cloud chambers to produced neutrons
  and determined their masses

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Subatomic particles
Actual mass (g)
Relative mass (amu)
Name
Symbol
Charge
Electron
e-
9.11 x 10-28
Proton
p
1.67 x 10-24
Neutron
n0
1.67 x 10-24
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Studdy Buddy Review

• Name three subatomic particles.
• Who is credited with discovering each particle?
• Describe the Rutherford Gold Foil Experiment.

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Models of the Atom
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Dalton Model of Atom

• Small, indivisible spheres

http//images.search.yahoo.com/search/images/
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J.J. Thompsons Model of Atom

• Plum Pudding Model, 1896
• Thought an atom was like plum pudding
• Dough was
• Raisins
• Didnt know about neutrons at this time

http//images.search.yahoo.com/search/images/
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Rutherfords Model of the Atom

• Rutherford Model, 1911
• Thought atom was mostly empty space
• Nucleus
• Electrons (negatively charged)

http//images.search.yahoo.com/search/images/
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Bohrs Model of the Atom

• Neils Bohr, 1913
• Similar to Rutherfords model
• Thought atom was mostly empty space
• Nucleus in center is dense, positively charge
• Electrons

http//images.search.yahoo.com/search/images/
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(Modern) Quantum Mechanical Model of the Atom

• Heisenberg, Schrodinger, many others, 1926
• Think atom is mostly empty space
• Nucleus in center is dense, positively charge
• Electrons
• Cannot locate

http//particleadventure.org/particleadventure/fra
meless/modern_atom.html
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References

• Dr. Stephen L. Cotton, Charles Page High School
• Ms. Manes