History of Atomic Models and Discoveries

What are the three key ideas of John Dalton's atomic theory presented in 1803?

1. Matter is made of atoms, which are tiny particles that cannot be created, destroyed, or divided. 2. Atoms of the same element are identical, while atoms of different elements are different. 3. Different atoms combine to form new substances.

What fundamental feature of science is illustrated by Dalton's atomic theory?

New experimental evidence may lead to a scientific model being changed or replaced.

What significant discovery did J.J. Thomson make in 1897?

He discovered the electron as a negatively charged subatomic particle.

What is the plum pudding model proposed by J.J. Thomson?

A model depicting negative electrons spread throughout soft globules of positively charged material.

What experiment did Ernest Rutherford conduct in 1909, and what was its significance?

He conducted the gold foil experiment, which showed that most of an atom's mass is concentrated in a nucleus, leading to the rejection of the plum pudding model.

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

Some positively charged particles were scattered or deflected, indicating that atoms consist mainly of empty space with a nucleus at the center.

What is the nuclear model of the atom as proposed by Rutherford?

A model where the atom consists mainly of empty space, with a nucleus at the center and electrons orbiting around it.

How did the nuclear model differ from the plum pudding model?

In the plum pudding model, electrons were embedded within a positive sphere, while in the nuclear model, the nucleus is a positive structure at the center with electrons orbiting around it.

What did Niels Bohr propose in 1913 regarding electron orbits?

He proposed that electrons orbit the nucleus in fixed shells or orbitals located at set distances from the nucleus.

What did Bohr's model explain about atomic structure?

It explained why the atom does not collapse inwards due to the attraction between the positive nucleus and negative electrons.

What did further investigation after Bohr's model reveal about the nucleus?

The nucleus could be divided into smaller particles, leading to the discovery of the proton.

When was the neutron proposed, and by whom?

In 1920, Rutherford proposed the existence of large, neutral particles within the nucleus.

Who provided evidence for the existence of neutrons, and when?

James Chadwick published evidence for neutrons in 1932, based on experiments by Frédéric and Irène Joliot-Curie.

What was the significance of the discovery of the neutron?

It explained the differences between atomic mass and atomic number of atoms.

What did the Bohr model contribute to atomic theory?

It introduced the concept of fixed electron orbits and energy levels associated with those orbits.

How did Bohr's model align with experimental results?

Bohr's theory and calculations agreed with experimental results, confirming the model's validity.

What was the primary focus of Rutherford's gold foil experiment?

To investigate the structure of the atom by observing the behavior of positively charged particles passing through gold foil.

What did Rutherford conclude about the atom's structure based on his experiment?

He concluded that the atom has a small, dense nucleus that contains most of its mass.

How did the concept of atomic structure evolve from Dalton to Bohr?

It evolved from Dalton's indivisible atoms to Thomson's divisible atoms, then to Rutherford's nuclear model, and finally to Bohr's fixed orbits.

What was the role of the cathode-ray tube in Thomson's discovery?

It was used to conduct experiments that led to the identification of the electron.

What did the discovery of the electron challenge in earlier atomic theories?

It challenged the notion that atoms were indivisible, as proposed by Dalton.

What does the term 'fixed shells' refer to in Bohr's model?

It refers to the specific energy levels at which electrons orbit the nucleus.

What was the impact of Rutherford's findings on the plum pudding model?

Rutherford's findings led to the rejection of the plum pudding model and the acceptance of the nuclear model.