The Modern Theory

The Modern Theory


In this lesson, you are continuing your investigation into the history of the atom by looking at the advancement of atomism since the electron. You can use the resources linked to from this esheet to conduct your investigation.


To begin your exploration of the modern atomic theory, go to and read each section of Electrons in Atoms, a chronological timeline marking milestones from 1897 to the present in the advancement of atomism since the electron.

Use the information from this resource to help you complete the word match on the Electrons in Atoms student sheet.

Now you should continue your investigation by reading A Summary of Particle Physics, which briefly describes the evolution of particle physics from the early 1900s to the present. As you go through this resource, think about your answers to these questions, which you can record on your Particle Physics student sheet:

  • What questions did scientists seek to answer about the fundamental structure of matter by the mid-1930s?
  • How did the use of accelerators advance and propel the study of the subatomic world?
  • What was significant about the quark proposal of 1964?
  • In terms of particle forces and interactions, why has gravitational forces been excluded from the Standard Model?
  • Why are strong and weak interactions important?
  • In what sense is today’s Standard Model incomplete? How do particle physicists plan to answer the questions that remain?

Next, read and review these two sections from the Particle Physics Timeline:

Answer these questions on your Particle Physics student sheet:

  • Which discoveries do you think are the most significant, interesting? Why?
  • Which discoveries do you think are the least significant, interesting? Why?
  • What inventions or benefits to society do you think subatomic discoveries like these are going to lead to?
  • What other kinds of subatomic discoveries do you think scientists might uncover in the years ahead?
  • What problems or dangers do you foresee coming from this level of high-powered, scientific investigation? Is the world better off not knowing how the subatomic world works? Why or why not?
  • How does learning the history of modern atomic theory help you in your scientific studies of the same subject?

Finally, your teacher may ask you to look at these resources on Particle Adventure:

  • What Is Fundamental?
  • What Is the World Made Of?
  • What Holds It Together?

This esheet is a part of the The History of the Atom 5: The Modern Theory lesson.

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Esheet Details

Grades Project 2061 Benchmarks National Science Standards