Lec 2 | MIT 5.112 Principles of Chemical Science, Fall 2005

TL;DR

Ernest Rutherford's backscattering experiment led to the discovery of the nucleus, a small and positively charged center of the atom. The classical model of the atom describes the electron moving in a fixed circular orbit around the nucleus.

Transcript

The following content is provided by MIT OpenCourseWare under a Creative Commons license. Additional information about our license and MIT OpenCourseWare in general is available at ocw.mit.edu. Great. Well, let's get going. Last time we ended up by discovering the electron. We discovered the fact that the atom was not the most basic constituent of ... Read More

Key Insights

• 🫀 The discovery of the nucleus by Ernest Rutherford in 1911 revolutionized the understanding of atomic structure.
• 🈂️ Rutherford's backscattering experiment revealed the presence of a small, positively charged nucleus surrounded by negatively charged electrons.
• 🫀 The classical model of the atom, based on the planetary model, described the electron moving in a fixed circular orbit around the nucleus.
• 🫀 Rutherford's experiment laid the foundation for future advancements in atomic theory and the understanding of atomic structure.
• 🫀 The size of the nucleus is much smaller compared to the diameter of the atom, indicating that atoms are mostly empty space.
• 🖐️ The Coulomb force plays a crucial role in keeping the electron and the nucleus together, with the force increasing as the distance between them decreases.
• 🥺 Rutherford's experiment and the discovery of the nucleus led to further research and the development of quantum mechanics to accurately describe atomic behavior.

Questions & Answers

Q: How did Ernest Rutherford discover the presence of the nucleus?

Rutherford conducted an experiment with alpha particles emitted from radium bromide and observed that while most particles went through a thin gold foil, a small fraction were backscattered, indicating the presence of a small, positively charged nucleus.

Q: What is the size of the nucleus compared to the atom?

The diameter of the nucleus is about 10^-14 meters, much smaller compared to the diameter of the atom, which is about 10^-10 meters.

Q: What is the charge of the nucleus?

Rutherford concluded that the nucleus has a positive charge, as it was known that atoms were neutral and contained electrons.

Q: How did Rutherford measure the diameter of the nucleus?

Rutherford measured the angular distribution of alpha particles scattered from the nucleus to determine the charge on the nucleus, which was found to be plus Z times e, where Z is the atomic number.

Summary & Key Takeaways

• In 1911, Ernest Rutherford discovered that the atom is not the most basic unit of matter and conducted an experiment with alpha particles emitted from radium bromide.

• Rutherford observed that most of the alpha particles went through a thin gold foil, but a small fraction were backscattered, indicating the presence of a small, positively charged nucleus.

• The nucleus was found to be very dense and much smaller in size compared to the atom, with a diameter of about 10^-14 meters.

• Rutherford's experiment and discovery of the nucleus formed the basis for the classical model of the atom, where the electron moves in a uniform circular orbit around the nucleus.