Ancient Atomic Theory

Learning Goals Students will: Understand the improvements to the Atomic Model through history Understand how each advancement leads to the present model of the atom.

Success Criteria Students will: Record the important facts in an information chart. Understand the advancements of each new atomic model. Identify the weakness of the model that lead to further investigation.

Presentation Outline Introduction Leucippus and Democritus Empedocles and Aristotle Aristotle and St. Thomas Aquinas and the effect of the Church The Alchemists

Introduction Atomic theory first originated with Greek philosophers around 2500 years ago. This basic theory remained unchanged until the 19th century when it first became possible to test the theory with more sophisticated experiments. As science has rapidly advanced over the past few centuries the atomic theory has been refined in accordance with the accepted scientific principles and theories of the time. Advances in technology and theory that have allowed experiments to be designed that enable us to probe matter to microscopic scales.

Ancient Atomic Theory The atomic theory of matter was first proposed by Leucippus, a Greek philosopher who lived at around 400BC. At this time the Greeks were trying to understand the way matter is made. But according to Leucippus, it is possible to subdivide matter in smaller and smaller parts, and he proposed that this process can be continued until eventually you arrive at small particles which can not be further subdivided. Leucippus called these indivisible particles atoms (from the Greek word atomos, meaning “indivisible”). Leucippus

Ancient Atomic Theory continued.. Leucippus's atomic theory was further developed by his disciple, Democritus Democritus suggested the atomic theory, explaining that all things are "composed of minute, invisible, indestructible particles of pure matter which move about eternally in infinite empty space“. This was the atom. Democritus

Problems Leucippus and Democritus were on the right track but they were PHILOSOPHERS NOT OF THESE THEORIES WERE EVER TESTED EXPERIMENTALLY Given the simple technology – it was difficult to test these theories

Ancient Atomic Theory continued.. According to the ancient Greeks, atoms were all made of the same basic material, but atoms of different elements had different sizes and shapes. The sizes, shapes, and arrangements of a material’s atoms determined the material’s properties. Another Greek Philosopher, Empedocles, proposed the 4-element theory of matter – in which all matter was seen to consist of Air, Fire, Water and Earth.

Aristotle Around 340 B.C. Aristotle said he didn't believe in the theory of Atoms because you would be putting a restriction on the gods. If the gods wanted to divide an element to something smaller than an atom, they could. The concept that God or gods had unlimited power was quite popular. In addition Aristotle introduced the fifth element (ether) that he said all heavenly bodies (Sun, moon, and stars, etc.) were made of. Hence ether was a heavenly material

St. Thomas Aquinas Aquinas was one the great philosophers of the Catholic Church. He used logic to prove the existence of God and used the teachings of Aristotle as a basis for his thinking. As a result the Catholic Church followed Aristotle’s 5-element theory. Since it was considered blasphemy to question the teachings of the church, most people (including scientists) did not question the 5-element theory. As a result, Aristotle’s the 5-element theory existed for over 2000 years.

Modern Astronomy vs. The Church Famous Astronomers Galileo and Copernicus believed that the Sun was in the middle of the solar system and not the Earth. This conclusion was based on many years of careful data collection by many scientists, yet the Church was convinced that God placed man at the center of the universe. Galileo was forced to recant his theory and his life was spared but he was placed under house arrest for the rest of his life.

Alchemy Alchemists were a combination of scientist, wizard, medicine man and philosopher. They believed in the 5-element theory of matter and made some developments to Science in the Middle Ages (1000 – 1500). Alchemists also made many biased, incorrect conclusions based on poor scientific reasoning. Since Aristotle believed that the fifth element could turn cheap metals into gold and cure disease and old age. Many alchemists pursued the discovery of the 5th element.

An alchemist expelling demons Alchemists An alchemist conducting experiments with his elves An alchemist expelling demons

Changes in Scientific Thinking Alchemists do take the credit for developing many types of glassware used today in Chemistry, as well as many experimental processes. BUT they made few scientific advances. Modern science did not begin until scientists: Began using careful experimental techniques to make observations Made conclusions based on these experiments with no biases. This led many early scientists into trouble from the Church.

The Modern Atomic Theory For centuries scientists did not have the methods or technology to test their theories about the basic structure of matter, so people accepted the ancient Greek view. In the 19th century John Dalton made inferences that exhibited how atoms bond together in definite proportions. Dalton was able to say that atoms of different elements combine in whole number ratios. John Dalton