Which experiment led to the discovery of the positively charged nucleus?

Which experiment led to the discovery of the positively charged nucleus?

• A. Thomson's cathode ray experiment
• B. Rutherford's gold foil experiment
• C. Pasteur's fermentation experiment
• D. Bohr's atomic model proposal

Answer: (B)

Atoms have a tiny, dense center that carries a positive charge. In Rutherford's gold foil experiment, a beam of positively charged alpha particles was aimed at a very thin sheet of gold. Most particles went straight through, but some were deflected at large angles, and a few even rebounded. If the atom were a uniform smear of positive charge with spread-out electrons (as in earlier models), most alpha particles would pass with little deflection. The large deflections could only occur if there’s a very small region in the center that is densely packed and positively charged, causing strong repulsion when an alpha particle came close. This led to the conclusion that the atom has a nucleus—a compact, positively charged core surrounded by mostly empty space. The other experiments don’t point to this central structure: Thomson’s cathode ray experiment revealed electrons and a diffuse positive distribution rather than a nucleus; Pasteur’s work dealt with biology, not atomic structure; Bohr’s model later described electron orbits around a nucleus but did not reveal the nucleus itself.

Atoms have a tiny, dense center that carries a positive charge. In Rutherford's gold foil experiment, a beam of positively charged alpha particles was aimed at a very thin sheet of gold. Most particles went straight through, but some were deflected at large angles, and a few even rebounded. If the atom were a uniform smear of positive charge with spread-out electrons (as in earlier models), most alpha particles would pass with little deflection. The large deflections could only occur if there’s a very small region in the center that is densely packed and positively charged, causing strong repulsion when an alpha particle came close. This led to the conclusion that the atom has a nucleus—a compact, positively charged core surrounded by mostly empty space.

The other experiments don’t point to this central structure: Thomson’s cathode ray experiment revealed electrons and a diffuse positive distribution rather than a nucleus; Pasteur’s work dealt with biology, not atomic structure; Bohr’s model later described electron orbits around a nucleus but did not reveal the nucleus itself.