Why did Thomson conclude that electrons are present in all atoms?
J.J. Thomson concluded that electrons are present in all atoms based on his experiments with cathode rays. He studied the conduction of electric current through gases at very low pressure and observed that cathode rays were streams of negatively charged particles, which were later called electrons.
He reached this conclusion because the nature of cathode rays was independent of the material of the cathode and the gas filled in the cathode ray tube. Since the properties of these particles remained the same regardless of the element or gas used, it proved that these particles are a fundamental component of all atoms, present in every element.
Explanation
The textbook explicitly states that the nature of cathode rays was independent of the cathode material and the gas used in the tube. This universality led Thomson to deduce that the negatively charged particles (electrons) making up these rays must be a fundamental component of all atoms, regardless of the element.
Solution Steps
Step 1: Identify that Thomson studied cathode rays in a discharge tube.
Step 2: Note that cathode rays consist of negatively charged particles (electrons).
Step 3: State the key observation: the nature of these rays was independent of the cathode material and the gas used.
Step 4: Conclude that because the rays were identical regardless of the substance, electrons must be a fundamental component of all atoms.