Modelos Atômicos I Dia 01 | Desafio de Carnaval

Summary

This lesson provides an in-depth exploration of atomic models, from ancient Greek philosophers like Leucippus and Democritus to modern models proposed by scientists such as Dalton, Thomson, Rutherford, and Bohr. It covers the evolution of atomic theory, starting with Dalton's billiard ball model and the discovery of the electron by Thomson. Rutherford's planetary model, based on his gold foil experiment, follows, leading to Bohr's quantum leap with stationary orbits for electrons. The lesson also touches on key concepts like isotopes, radioactivity, and the relationship between energy and electrons in atomic structure.

Takeaways

• 😀 The concept of the atom dates back to 500-400 BC with Greek philosopher Leucippus, who proposed that matter is not infinitely divisible and must have a smallest indivisible part called the 'atom.'
• 😀 Democritus, a disciple of Leucippus, helped spread the idea of atoms, though philosophers like Plato and Aristotle rejected the notion for many years.
• 😀 In the early 1800s, John Dalton revived atomic theory, introducing the 'billiard ball' model, where atoms are indivisible spheres, based on the law of constant proportions and mass conservation.
• 😀 Dalton’s atomic postulates included: elements consist of atoms, atoms of the same element are identical, atoms combine in fixed proportions, and during chemical reactions, atoms are conserved.
• 😀 Some of Dalton's postulates have been disproven: atoms are not indivisible, as discovered through radioactivity, and atoms of the same element can differ in mass (isotopes).
• 😀 Thomson's atomic model, known as the 'plum pudding' model, suggested that atoms have a positively charged 'pudding' with negatively charged 'raisins' (electrons) embedded within it.
• 😀 The discovery of cathode rays by J.J. Thomson showed that atoms contain negatively charged particles (electrons) that are much smaller than hydrogen atoms.
• 😀 The discovery of radioactivity by Henri Becquerel and Marie and Pierre Curie led to new insights, and Ernest Rutherford used this to conduct experiments that led to the planetary model of the atom.
• 😀 Rutherford’s gold foil experiment revealed that atoms have a small, dense, positively charged nucleus at the center, with electrons orbiting in large, mostly empty space around it.
• 😀 Niels Bohr’s atomic model explained that electrons exist in fixed energy levels (or orbits) and absorb or emit energy when they move between these orbits. This model incorporated quantum mechanics concepts like 'quanta' and 'photons.'

Q & A

What was the first idea of the atom proposed by Leucippus?

Leucippus proposed that matter is not infinitely divisible, and there comes a point where it cannot be divided further. He called this indivisible part 'atomos', meaning 'indivisible' in Greek.

How did Dalton contribute to atomic theory?

Dalton revived the atomic concept in the early 1800s, proposing that atoms are indivisible and form the basis of chemical elements. He supported his theory with the laws of chemical combination and introduced several postulates about the nature of atoms.

What were Dalton's main postulates regarding atoms?

Dalton's postulates included: 1) All elements are made up of atoms. 2) Atoms are indivisible and indestructible. 3) Atoms of the same element are identical. 4) Atoms combine in fixed mass ratios to form compounds. 5) In chemical reactions, atoms are conserved.

Which of Dalton's postulates have been proven false?

Several of Dalton's postulates were later proven false. For instance, atoms are not indivisible, as radioactivity showed that atoms can decay and transform into other elements. Additionally, atoms of the same element can differ (isotopes), meaning they are not always identical.

What was Thomson's contribution to atomic theory?

Thomson discovered the electron while studying cathode rays. He proposed the 'plum pudding model' of the atom, where negative electrons were embedded in a positive 'goo'. This was the first model to account for the atom's electrical nature.

How did J.J. Thomson's experiments lead to the discovery of the electron?

Thomson's experiments with cathode rays led him to conclude that these rays were composed of negatively charged particles. He showed that these particles had mass and could be deflected by electric fields, leading to the discovery of electrons.

What was the result of Rutherford's gold foil experiment?

Rutherford's gold foil experiment showed that most alpha particles passed through the foil, but some were deflected at large angles, and a few even bounced back. This led him to propose the existence of a small, dense, positively charged nucleus at the center of the atom.

How did Rutherford's findings differ from Thomson's atomic model?

Rutherford's findings contradicted Thomson's 'plum pudding' model, which suggested that positive charge was spread throughout the atom. Rutherford's experiment showed that the positive charge was concentrated in a small nucleus, surrounded by mostly empty space with electrons orbiting around it.

What is Bohr's model of the atom, and how did it address Rutherford's shortcomings?

Bohr's model introduced the concept of quantized orbits for electrons. Unlike Rutherford's model, Bohr proposed that electrons occupy specific orbits with fixed energies and do not radiate energy while in those orbits. This explained why electrons don't spiral into the nucleus.

How did the quantum theory contribute to Bohr's model?

Bohr used the principles of quantum mechanics to explain the stability of electron orbits. He introduced the concept of 'quanta' of energy, meaning electrons could only occupy orbits with specific energy levels, and could absorb or emit energy in discrete amounts when transitioning between orbits.