Question

1. both democritus and dalton proposed that matter consists of atoms. explain how their approaches to reaching the same conclusion differed.

1. describe the experiment that led to the discovery of the electron.

1. describe rutherford’s gold foil experiment. what did this experiment tell us about the structure of the atom?

1. what are the 3 subatomic particles? describe the differences between them in their masses, charges, and place within the atom.

1. since all atoms have negatively charged electrons, shouldn’t every atom have a negative charge? explain.

Explanation:

Question 5: Describe the experiment that led to the discovery of the electron.

J.J. Thomson's cathode - ray tube experiment: A cathode - ray tube has a cathode (negative electrode) and an anode (positive electrode) in a vacuum - sealed tube. When a high voltage is applied, a ray (cathode ray) travels from the cathode to the anode. Thomson observed that these rays were deflected by electric and magnetic fields. The deflection showed that the rays were made of negatively charged particles (later named electrons). He also calculated the charge - to - mass ratio ($\frac{e}{m}$) of these particles, proving electrons are subatomic particles present in all atoms.

• Experiment: Rutherford directed alpha particles (positively charged, from radioactive decay) at a thin gold foil. A fluorescent screen around the foil detected alpha - particle hits.
• Observations: Most alpha particles passed through the foil (atom is mostly empty space). Some were deflected at small angles, and a few were deflected back (hit a dense, positively charged core - the nucleus).
• Atomic structure conclusion: Atom has a small, dense, positively charged nucleus at the center, with electrons orbiting in the mostly empty space around it.

• Proton: Mass ≈ $1.67\times10^{-27}\ kg$ (or 1 atomic mass unit, amu), charge = +1, located in the nucleus.
• Neutron: Mass ≈ $1.67\times10^{-27}\ kg$ (or 1 amu), charge = 0, located in the nucleus.
• Electron: Mass ≈ $9.11\times10^{-31}\ kg$ (negligible compared to proton/neutron), charge = - 1, located in electron cloud (outside nucleus).

Answer:

J.J. Thomson's cathode - ray tube experiment: A high - voltage is applied in a vacuum - sealed tube with cathode and anode. Cathode rays (electron - carrying) are deflected by electric/magnetic fields, showing they have negative charge. Thomson calculated $\frac{e}{m}$, proving electrons are subatomic.

Question 6: Describe Rutherford’s gold foil experiment. What did this experiment tell us about the structure of the atom?