Discovery and Structure of the Atom
The evolution of atomic theory began with Democritus's concept of "atomos" and progressed through several groundbreaking discoveries. John Dalton established the first comprehensive atomic theory, proposing atoms as solid spheres. Thomson's cathode ray experiments revealed electrons and led to the plum pudding model, while Millikan's oil drop experiment determined the electron's charge.
Highlight: Rutherford's gold foil experiment proved atoms were mostly empty space with a dense, positive nucleus.
Definition: Subatomic particles consist of protons mass1amu,charge+1, neutrons mass1amu,charge0, and electrons mass0amu,charge−1.
Vocabulary: Isotopes are atoms with the same number of protons but different numbers of neutrons.
Example: Nuclear symbol notation for hydrogen-3 can be written as ³H or Hydrogen-3.
Quote: "Atomic number is the number of protons, and in a neutral atom, also equals the number of electrons."