Chapter 5Chapter 5Early Atomic Theory Early Atomic Theory

and Structureand Structure

The History The History of the of the Atom…Atom…

ObjectivesObjectives

• History of Atomic Theory (5.1-History of Atomic Theory (5.1-5.5, 5.7)5.5, 5.7)

• Subatomic Particles (5.5, 5.8)Subatomic Particles (5.5, 5.8)• Atomic Numbers (5.9)Atomic Numbers (5.9)• Isotopes (5.10)Isotopes (5.10)• Atomic Mass (5.11)Atomic Mass (5.11)

Democritus of Abdera

• ~460 BC to 370 BC

• World made of

• Student of Leucippus

Democritus of Abdera1)1) All matter is composed of All matter is composed of

2)2) There is a void, which is empty There is a void, which is empty space between atomsspace between atoms

3)3) Atoms are Atoms are 4)4) Atoms are Atoms are

5)5) Atoms differ in Atoms differ in

Aristotle• Opposed ideas

of Democritus• Empedoclean

theory–

• Ideas dominate into 17th century…

Atomism in Antiquity• Church spoke Church spoke

against atomsagainst atoms– Did not support Did not support

God creating God creating earthearth

Atomism in the Middle Ages

• Artistotle’s works rediscovered (1200s)

• Catholic ChurchCatholic Church–

• De Rerum Natura De Rerum Natura rediscovered in rediscovered in 14171417– Prime source for Prime source for

ideas of Leucippus ideas of Leucippus and Democritusand Democritus

Atomism in the Renaissance

• Dominated by Alchemists–

• Discovery of many Discovery of many elementselements

• Preparation of Preparation of mineral acidsmineral acids

Robert Boyle (1627-1691)

• Matter is divided Matter is divided into little into little

• First to perform First to perform truly quantitative truly quantitative experimentsexperiments–

Antoine Laurent Antoine Laurent LavoisierLavoisier

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

Amadeo AvogadroAmadeo Avogadro•(1776-1856)•

John DaltonJohn Dalton•(1766-1844)•Englishman•School teacher•

John DaltonJohn Dalton1.All matter is 2.Atoms of the

3.Atoms cannot

John DaltonJohn Dalton4. Atoms of

5. In chemical reactions, atoms are

John DaltonJohn Dalton

Law of Multiple Law of Multiple ProportionsProportions

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

J. J. ThomsonJ. J. Thomson•1856-1940•Showed experimentally the existence of

J. J. ThomsonJ. J. Thomson•Cathode Tube Experiment

J. J. ThomsonJ. J. Thomson

Robert A. MillikanRobert A. Millikan

•DetermineDetermined charge of d charge of an electronan electron

•NegativeNegative

Ernest RutherfordErnest Rutherford•1871-1937•Defined

•

Ernest RutherfordErnest Rutherford

The Modern Day Atom• Nucleus:

–

• Orbiting Nucleus:

Atomic Numbers (Z)• Equal to number of •

Mass Number (A)• Sum of

Isotopes of the Elements• Same atomic number but • Different number of

Ions of the Elements

•Same number of •Has lost or gained

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)– – –