Chapter 4.2, Problem 12LC

Interpretation Introduction

Interpretation : Thomson’s and Millikan’s contribution to atomic theory is to be explained.

Concept Introduction : Thomson was the person behind the discovery of electrons that revolve around the nucleus. Mulliken performed tests to determine the magnitude of an electron's charge.

Answer to Problem 12LC

Thomson concluded that electrons are a part of every element’s atom.

Mulliken calculated the mass of an electron by the value of its charge and Thomson’s electron charge to mass ratio.

Explanation of Solution

Thomson tested low-pressure gases while an electric current was running through them.

To validate his theory, Thomson devised an experiment to ascertain the charge-to-mass ratio of an electron. This ratio was found to be constant.

The charge-to-mass ratio of electrons was unaffected by the cathode ray tube's gas composition or the metal used for the electrodes.

Thomson concluded that every element's atom contains electrons.

Mulliken performed tests to determine the magnitude of an electron's charge. In his experiment,

• Mulliken used two charged plates to suspend negatively charged oil droplets in his oil-drop experiment.
• He then altered the voltage on the plates to observe how the droplet's rate of fall was impacted. He discovered that each oil droplet had a charge that was a multiple of $1.6\times {10}^{-19}\text{coulomb}$, indicating that it was an electron's charge.
• Mulliken calculates an electron’s mass by using the charge value and Thomson’s charge-to-mass ratio of an electron.
• An electron has one unit of a negative charge, and its mass is 1/1840 the mass of a hydrogen atom.