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
• World made of
• Student of Leucippus

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Democritus of Abdera

1. All matter is composed of
2. There is a void, which is empty space between
   atoms
3. Atoms are
4. Atoms are
5. Atoms differ in

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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
• Did not support God creating earth

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Atomism in the Middle Ages

• Artistotles works rediscovered (1200s)
• Catholic Church
• De Rerum Natura rediscovered in 1417
• Prime source for ideas of Leucippus and Democritus

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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
• First to perform truly quantitative experiments

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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

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John Dalton

• All matter is
• Atoms of the
• Atoms cannot

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John Dalton


4. Atoms of 5. In chemical reactions, atoms
are




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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




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J. J. Thomson

• 1856-1940
• Showed experimentally the existence of

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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

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Ernest Rutherford





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The Modern Day Atom

• Nucleus
• Orbiting Nucleus

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Atomic Numbers (Z)

• Equal to number of

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Mass Number (A)

• Sum of

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Isotopes of the Elements

• Same atomic number but
• Different number of

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Ions of the Elements

• Same number of
• Has lost or gained

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Atomic Mass

• Measured in atomic mass units
• Equal to exactly 1/12 mass of a carbon-12 atom
• Average relative mass
• Average atomic mass (seen on periodic table)