Chapter 5 Early Atomic Theory and Structure

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Chapter 5Early Atomic Theory and Structure

• The History of the Atom

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Objectives

• History of Atomic Theory (5.1-5.5, 5.7)
• Subatomic Particles (5.5, 5.8)
• Atomic Numbers (5.9)
• Isotopes (5.10)
• Atomic Mass (5.11)

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Democritus of Abdera

• 460 BC to 370 BC
• Student of Leucippus

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Democritus of Abdera

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
3. Atoms are completely solid
5. Atoms differ in size, shape and weight

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Aristotle

• Opposed ideas of Democritus
• Empedoclean theory
• Ideas dominate into 17th century

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Atomism in Antiquity

• Church spoke against atoms

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Atomism in the Middle Ages

• Artistotles works rediscovered (1200s)
• Catholic Church
• De Rerum Natura rediscovered in 1417

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Atomism in the Renaissance

• Dominated by Alchemists
• Discovery of many elements
• Preparation of mineral acids

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Robert Boyle (1627-1691)

• Matter is divided into little particles of
  several sizes (corpuscles)
• First to perform truly quantitative experiments
• Pressure and volume of air

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Antoine Laurent LavoisierFather of Chemistry

• 1743-1794
• Matter can be changed but never created or
  destroyed
• Law of Conservation of Mass

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Antoine Laurent LavoisierFather of Chemistry


"It took them only an instant to cut off that
head, and a hundred years may not produce another
like it."




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Amadeo Avogadro

• (1776-1856)

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John Dalton

• (1766-1844)
• Englishman
• School teacher
• Developed atomic theory

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John Dalton

1. All matter is composed of atoms
3. Atoms cannot be subdivided, created or destroyed

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John Dalton


4. Atoms of different elements combine in small
whole numbers 5.




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John Dalton


Law of Multiple Proportions When two elements
form a series of compounds, the ratios of the
masses of the second element that combine with 1
gram of the first element can always be reduced
to small whole numbers CO, CO2, CO3, etc.




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J. J. Thomson

• 1856-1940
• Showed experimentally the existence of the
  electron

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J. J. Thomson

• Cathode Tube Experiment

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J. J. Thomson





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Robert A. Millikan

• Determined charge of an electron
• Negative

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Ernest Rutherford

• 1871-1937
• Defined radioactivity
• Named alpha and beta particles

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Ernest Rutherford





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Ernest Rutherford





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The Modern Day Atom

• Nucleus
• Orbiting Nucleus

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Atomic Numbers (Z)

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Mass Number (A)

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Isotopes of the Elements

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Ions of the Elements

• Same number of protons and neutrons

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Atomic Mass

• Measured in atomic mass units
• Average relative mass of the isotopes of that
  element compared to the atomic mass of carbon-12
• Average atomic mass (seen on periodic table)