Question

(2:50)
what did john dalton contribute to atomic theory?
the discovery of protons
the nuclear model of the atom
the first scientific atomic theory based on evidence
the discovery of isotopes

(4:20)
j.j. thomsons experiments with cathode rays led to which discovery?
the neutron
the nucleus
the electron
the proton

Explanation:

• For the first question: John Dalton proposed the first scientific atomic theory based on evidence. Protons were discovered by Ernest Rutherford (through experiments with alpha - particles and nitrogen gas). The nuclear model of the atom was proposed by Ernest Rutherford (gold - foil experiment). Isotopes were discovered later, and Dalton's theory initially assumed all atoms of an element were identical.
• For the second question: J.J. Thomson's experiments with cathode rays led to the discovery of the electron. The neutron was discovered by James Chadwick. The nucleus was discovered by Ernest Rutherford. The proton was also discovered by Ernest Rutherford (in his work on the nuclear model and through experiments with hydrogen).

Answer:

• (2:50) The first scientific atomic theory based on evidence
• (4:20) The electron