How Has Our Understanding of the Atom Changed Since Thomson's Model?

[Air]

Question:
In 1997 we celebrated the centenary of JJ Thomson’s discovery of the electron. Thomson pictured the atom as being like a currant bun, with electron ‘currants’ embedded in a positively charged ‘bun’. Give a short account of three ways in which our model of matter on a subatomic scale has changed since Thomson’s discovery. For each, state clearly how the model changed, and write a few sentences outlining one piece of evidence that played a part in bringing about the change.

My response:
I've outline the point, but cannot expand on it, can I have help on the detail:

• Nuclear atom - Alpha scattering: large angles. Incompatible with bun model.
• Protons and neutrons in nucleus - Chadwick’s experiment: neutral particle of same mass as H.
• Quarks (existence of) - Deep inelastic scattering: structure within proton.
• Momentum of electromagnetic radiation - de Broglie theoretical prediction.
• Antimatter Anderson’s observation of e - like particle with positive charge.
• Neutrinos - “Missing” energy in beta decay.

 

[Gokul43201]

1. It looks like you just pasted some tidbits about subatomic particles without actually looking to answer the given question,
2. You need to look up what different models of the atom involve,
3. There's a clear emphasis on electrons in the question - as there should be for a question on atomic structure - so don't ignore them.

 

[Moetasim]

Since JJ Thomson's discovery of the electron in 1897, our understanding of the subatomic world has undergone significant changes. The first major shift in our model of matter came with the discovery of the nucleus, which replaced Thomson's "currant bun" model. This change was brought about by the famous alpha scattering experiment conducted by Ernest Rutherford in 1911. This experiment involved firing alpha particles at a thin sheet of gold foil and observing their deflection. The results showed that most of the particles passed straight through, but a small percentage were deflected at large angles. This was incompatible with Thomson's model, as it suggested that the majority of the atom's mass was concentrated in a small, dense nucleus rather than being spread out evenly.

The next major change in our model of matter came with the discovery of protons and neutrons in the nucleus. This was made possible by James Chadwick's experiments in 1932, where he bombarded beryllium with alpha particles and observed the emission of a neutral particle with the same mass as a hydrogen atom. This discovery led to the development of the nuclear model of the atom, which placed protons and neutrons in the nucleus and electrons in orbit around it.

In the 1960s, the existence of even smaller particles within protons and neutrons was revealed through deep inelastic scattering experiments. This evidence, along with theoretical predictions by Louis de Broglie, led to the recognition of quarks as the fundamental building blocks of protons and neutrons.

Another significant change in our model of matter came with the discovery of antimatter. In 1932, Carl Anderson observed a positively charged particle with the same mass as an electron, which he named the positron. This discovery challenged the idea that all particles have a positive charge, as proposed by Thomson's model.

Finally, the existence of neutrinos was confirmed in the 1950s through the observation of "missing" energy in beta decay experiments. This evidence suggested that a neutral particle, later identified as the neutrino, was also involved in the process.

Overall, our understanding of the subatomic world has evolved significantly since Thomson's discovery of the electron. Through various experiments and theoretical predictions, we have come to understand the complex structure of matter on a subatomic scale and continue to make new discoveries and advancements in this field.