Seri Kimia Dasar - Atom, kok bisa ditemukan? (teori atom Democritus, Dalton, Thomson)

Summary

This video covers the history and development of atomic theory, starting from ancient Greek philosopher Democritus, who proposed that matter is made up of indivisible particles called 'atomos.' It then explores the advancements made by John Dalton in the 19th century, introducing key concepts like the law of conservation of mass and atomic theory. The video also delves into J.J. Thomson's discovery of the electron in 1897 through cathode ray experiments and presents the 'plum pudding' model of the atom. It concludes with a teaser for the next video discussing further atomic theories.

Takeaways

• 😀 Democritus, a Greek philosopher from 400 BCE, proposed that matter is made of indivisible particles called 'atomos.'
• 😀 Democritus believed atoms were solid, indivisible, and that there was empty space between them allowing movement.
• 😀 Aristotle and Plato rejected Democritus’ idea, instead supporting the concept of four basic elements: earth, air, water, and fire.
• 😀 Democritus’ atomic theory was largely forgotten for over 2200 years until John Dalton revived the idea in 1831.
• 😀 Dalton's atomic theory included key principles: matter is made of atoms, all atoms of an element are identical, and atoms combine in fixed ratios to form compounds.
• 😀 Dalton’s theory explained the conservation of mass in chemical reactions, stating mass is neither created nor destroyed.
• 😀 Dalton's work led to the understanding that chemical reactions involve the rearrangement of atoms, not their destruction or creation.
• 😀 While Dalton’s theory was groundbreaking, it was later challenged because it didn’t explain electrical conductivity and other phenomena.
• 😀 In 1897, J.J. Thomson discovered the electron through experiments with cathode rays, showing atoms contain negatively charged particles.
• 😀 Thomson’s 'plum pudding' model suggested that atoms were made of a positively charged 'pudding' with negatively charged electrons embedded in it.
• 😀 Thomson’s model was eventually challenged by Rutherford’s gold foil experiment, which led to further developments in the understanding of atomic structure.

Q & A

What was Democritus' theory about atoms?

Democritus proposed that matter is composed of indivisible particles called 'atomos', meaning 'uncuttable'. He believed that if a piece of matter, like a stone, was repeatedly divided, it would eventually reach a point where it couldn't be divided further. These atoms were believed to be solid, indivisible, and without internal structure.

How did Democritus view the structure of atoms?

Democritus thought that atoms had no internal structure, were solid, and were spaced apart with empty space (void) between them, allowing them to move freely.

What was the opposing view to Democritus' atomic theory?

Philosophers like Aristotle and Plato opposed Democritus' theory. They believed that matter was made of four elements: earth, air, fire, and water, and they argued that dividing matter endlessly would not lead to atoms but would simply result in the disappearance of matter.

What significant contribution did John Dalton make to atomic theory?

John Dalton revived the study of atoms in the 19th century, proposing that matter is made of indivisible atoms. He also formulated the laws of definite composition and the conservation of mass, helping to establish the modern understanding of atomic theory.

How did Dalton's model differ from Democritus' theory?

Dalton's model also proposed that atoms were indivisible, but he further defined that each element had atoms of the same mass and properties, unlike Democritus who only proposed atoms as indivisible particles without specific characteristics.

What was Dalton's Law of Definite Proportions?

Dalton's Law of Definite Proportions states that a chemical compound always contains the same elements in the same proportions by mass, regardless of the sample size or origin.

What is the Law of Conservation of Mass, and how does it relate to atomic theory?

The Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction. Dalton applied this law to atomic theory, asserting that atoms are rearranged in chemical reactions but not created or destroyed.

How did J.J. Thomson's experiment challenge Dalton's theory?

J.J. Thomson's experiment with cathode rays showed that atoms contain negatively charged particles, later named electrons. This discovery contradicted Dalton's theory, which depicted atoms as indivisible, and suggested that atoms had internal structure.

What was Thomson's Plum Pudding Model?

Thomson's Plum Pudding Model proposed that atoms were composed of a uniform, positively charged 'pudding' with negatively charged 'plums' (electrons) scattered throughout. This was an early model of atomic structure before the discovery of the atomic nucleus.

Why did Thomson's model have limitations?

Thomson's model failed to explain certain experimental observations, such as the scattering of alpha particles in Ernest Rutherford's gold foil experiment, which led to the discovery of the atomic nucleus and a new model of atomic structure.