(40) GCSE Chemistry Revision "Alpha-Scattering Experiment"

Introduction

• Overview of the video topic: Atomic Structure

• Learning objectives:

  • Describe the Plum Pudding model

  • Explain the results of the alpha scattering experiment and its implications for the nuclear model

Historical Background

• Ancient Greek Theory of Atoms:

  • Belief that everything is made of atoms, which were indivisible tiny spheres.

  • This idea remained accepted for hundreds of years.

Discovery of Electrons

• Year: 1897

• Key Discovery:

  • Atoms contain tiny negative particles called electrons.

  • This finding indicated that atoms have an internal structure rather than being simple indivisible spheres.

The Plum Pudding Model

• Definition:

  • Atoms are described as a sphere of positive charge with negative electrons embedded within.

• Origin of the Name:

  • Named after the appearance of Plum Pudding, where the positive charge represents the pudding and electrons represent the plums.

Alpha Scattering Experiment

• Importance:

  • Considered one of the most important experiments in science; shifted scientific understanding of atomic structure.

• Experimental Setup:

  • Use of gold foil (thin and only a few atoms thick).

  • Firing positively charged alpha particles at the gold foil.

• Observations:

  • Most alpha particles passed through the foil without deflection.

  • Some particles were deflected at angles.

  • A few particles bounced directly back.

Implications of Results from Alpha Scattering

• Conclusion 1:

  • Most alpha particles passing through demonstrated that atoms are mainly empty space; hence the Plum Pudding model was incorrect.

• Conclusion 2:

  • Deflected particles suggested that a positive charge exists in the center of the atom, repelling the positive alpha particles.

• Conclusion 3:

  • Particles that bounced back indicated that the center of the atom contains a significant amount of mass, leading to the concept of the nucleus.

Transition to the Nuclear Model

• Description of Nuclear Model:

  • Most of the atom is empty space.

  • A small, dense, positive nucleus at the center containing most of the atom's mass.

  • Negative electrons orbiting around the nucleus.

• Summary of Change:

  • The nuclear model replaced the Plum Pudding model due to new experimental evidence.