The Emergence of Ideas about the Atom.pptx

The Emergence of Ideas about the Atom

1. The Emergence of Ideas about the Atom

2. Ancient Greeks ‘Concept of the Atoms and the Elements The theory of the atom started in the 5 th century BCE in ancient Greece. Early Greek natural philosophers did not experiment to prove or disprove ideas; they simply made arguments for their claims.

3. One of the philosophers was Leucippus (480 BCE- 460 BCE) who first proposed the idea of an atom. He believed that all things are made up of tiny, indivisible particles.

4. Democritus (460 BCE- 370 BCE, a student of Leucippus, also thought the same way. He posited that all matter was composed of small indestructible particles, which he called atoms, from the Greek word atomos , which means “ indivisible ”

5. This idea meant that if you were to cut a piece of object ( matter) there would be a point wherein the object could no longer be further split into small piece. Thus, matter can be subdivided only to a certain point, at which only atoms remain. Those who supported Leucippus and Democritus’s idea of the atom were called atomist.

6. Leucippus and Democritus’s theory that atoms were indivisible was strongly opposed by Aristotle (384 BCE 322 BCE ). He believed that all things can be divided infinitely; therefore, he said there was no smallest part of matter.

7. He also claimed that all matter consisted of four elements- earth, fire, water, and air. Because Aristotle was more popular and influential during that time, many people accepted his idea.

8. Alchemists’ contributions to Modern Chemistry Alchemy is a medieval practice which aims to transform a metal into gold. In the 16 th and 17 th centuries, alchemy played a role in the scientific revolution particularly in the development of the atomic structure.

9. Alchemists tried to explain atomic theory based on experiments unlike the philosopher’s logical way of explaining .

10. Dalton’s Atomic Theory- The idea of atomic theory was revived by John Dalton (1766-1844) 2 000 years after Democritus first proposed about it.

11. Dalton formulated his theory based on Antoine Lavoisier’s (1743- 1794) law of conservation of mass and Joseph Proust’s ( 1754- 1826) law of definite proportion.

12. Law of Conservation of Mass Law of Definite Proportions The total mass of substances before and after a complete reaction is equal. Elements combine in a fixed proportion to form a compound.

13. The formulation of Dalton’s atomic theory marked the start of the modern era of chemistry. However, during his time (1800s), some scientists still did not believe that there was an indivisible atom found in all matter. Let us look at the cathode ray tube ( CRT) experiment.

14. The CRT is a glass tube with two electrodes: the positive electrode called anode and negative electrode called cathode.

15. When a gas is placed inside the tube and electricity passes through it, light rays ( cathode rays) will be released from the negative electrode and hit the positive electrode. Due to the invention of CRT, subatomic particles were discovered.