Modelos de Dalton e Thomson [Módulo 02 - Aula 01]

Summary

In this video, the evolution of atomic models is discussed, starting with the early philosophical ideas of Leucippus and Democritus, who proposed the concept of indivisible atoms. The script then covers John Dalton's billiard ball model, followed by J.J. Thomson's 'plum pudding' model, which introduced the idea of negatively charged electrons. Dalton's model suggested atoms were indivisible, while Thomson's showed that atoms were divisible and had electrical charges. The video also touches on experiments and exercises, helping viewers understand these fundamental concepts of atomic structure and their historical progression in science.

Takeaways

• 😀 The concept of the atom originates with philosophers Leucippus and Democritus, who proposed the idea of indivisible particles called 'atoms'.
• 😀 Aristotle's theory of the four elements (earth, fire, water, air) was more influential at the time and overshadowed the atomic theory for centuries.
• 😀 John Dalton revived the atomic theory in 1803, proposing that atoms are indivisible and have a solid, spherical structure, known as the 'billiard ball' model.
• 😀 Dalton's four postulates included: atoms of the same element are identical, atoms of different elements are different, chemical reactions involve rearranging atoms, and atoms are neither created nor destroyed in chemical reactions.
• 😀 Dalton's model could not explain phenomena such as the attraction between objects with different electric charges, which led to the development of new atomic models.
• 😀 J.J. Thomson proposed the 'plum pudding' model in 1898, based on his experiments with cathode rays, which showed the existence of negatively charged particles (electrons) inside atoms.
• 😀 Thomson's cathode ray experiments demonstrated that cathode rays were negatively charged, could be deflected by magnetic fields, and had mass.
• 😀 The 'plum pudding' model proposed that atoms consist of a positively charged sphere with electrons embedded within it, balancing the overall charge to make the atom neutral.
• 😀 Thomson's discovery of the electron marked a key advancement, as it showed that atoms were not indivisible, but made of smaller subatomic particles.
• 😀 The script ends with an exercise where the teacher verifies understanding of the atomic models, concluding that the correct answer to the problem is 'C', related to Thomson's discoveries.

Q & A

What was the original idea of the atom proposed by Leucippus and Democritus?

Leucippus and Democritus proposed that matter could be divided endlessly until reaching a particle that could no longer be divided, which they called the 'atom' (from the Greek word 'atomos', meaning indivisible).

Why did Aristotle's theory of the four elements delay the acceptance of the atomic model?

Aristotle's theory, which suggested that all matter was composed of combinations of four elements—earth, fire, water, and air—was more influential and widely accepted than the atomic theory, causing the concept of the atom to be overlooked for centuries.

What were the key postulates of Dalton’s atomic theory?

Dalton proposed that: 1) Atoms of the same element are identical; 2) Atoms of different elements are distinct; 3) Chemical reactions involve rearrangements of atoms; 4) Atoms are neither created nor destroyed in a chemical reaction.

What discovery challenged Dalton's model and led to the development of a new atomic model?

The discovery of electric charges in matter challenged Dalton’s model. The observation that certain materials exhibited electric charges led to the development of Thomson’s model, which introduced the concept of electrons.

What was the ‘pudding model’ of the atom proposed by J.J. Thomson?

Thomson’s 'pudding model' suggested that the atom was a large, positively charged sphere with negatively charged electrons embedded within it, much like raisins in a pudding.

What experimental evidence did Thomson use to support his atomic model?

Thomson used experiments with cathode rays, which were deflected by magnetic fields and demonstrated a negative charge, indicating the presence of negatively charged particles (electrons) in all matter.

How did Thomson’s discovery of electrons impact the concept of atomic indivisibility?

Thomson’s discovery of electrons showed that the atom was not indivisible, as previously thought, but rather made up of smaller, subatomic particles, making the atom divisible for the first time.

Why did Thomson conclude that electrons existed in all types of matter?

Thomson concluded that electrons existed in all matter because, regardless of the material used in his experiments, he consistently observed negatively charged particles (electrons) being emitted.

What was the main difference between Dalton’s and Thomson’s atomic models?

The main difference was that Dalton’s model considered atoms as indivisible particles, whereas Thomson’s model recognized that atoms were divisible and contained subatomic particles like electrons.

What important concept did Thomson contribute to atomic theory in terms of electric charge?

Thomson’s major contribution was the discovery of the electron, which provided the first evidence that atoms contained negatively charged particles, leading to the realization that atoms could have both positive and negative charges.