Early Atomic Days
Who first suggested that matter is made of tiny indivisible atoms?
Who is Democritus?
Which negatively charged particle was discovered using cathode ray tubes?
What is the electron?
Which type of radiation consists of helium nuclei?
What is alpha radiation?
Which atomic model described electrons embedded in a positive sphere?
What is the plum pudding model?
Who proposed that energy is emitted in discrete units called quanta?
Who is Max Planck?
Which scientist brought back the atomic theory by stating that atoms combine in simple whole-number ratios?
Who is John Dalton?
What key observation in Thomson’s experiment proved that cathode rays were negatively charged?
They were deflected by electric and magnetic fields.
Which type of radiation has the greatest penetrating power?
What is gamma radiation?
Which model first introduced a central nucleus?
What is the Rutherford model?
Who suggested electrons have wave-like properties?
Who is Louis de Broglie
Which discovery showed atoms could break apart, challenging Dalton’s idea of indivisible atoms?
What is radioactivity
What was Millikan able to calculate once he measured the electron’s charge?
The mass of the electron.
What observation proved that light energy depends on frequency?
The photoelectric effect.
Why would electrons in the Rutherford model be unstable according to physics?
They should lose energy and spiral into the nucleus.
What does Schrödinger’s wave equation describe instead of exact electron paths?
Electron probability distributions (orbitals).
Why did Dalton’s atomic theory fail to explain isotopes?
Because atoms of the same element can have different masses.
Explain Rutherford's gold foil experiment?
Rutherford fired alpha particles at a thin gold foil. Most passed straight through, showing that atoms are mostly empty space, while some were deflected.
Why could the wave theory not explain the photoelectric effect?
Increasing light intensity did not eject electrons unless the frequency was high enough.
How did Bohr’s model solve the problem of atomic stability?
By placing electrons in fixed, quantized energy levels.
Why can electrons not be described as moving in fixed circular orbits?
Because their wave nature causes uncertainty in position and momentum.
Which particle’s discovery explained isotopes and atomic mass differences?
What is the neutron?
How did the results of the gold foil experiment prove Thomson’s plum pudding model false?
The deflections showed that a positively charged mass is concentrated in the nucleus, unlike Thomson's model, which spread evenly throughout the atom.
How did Einstein’s explanation of the photoelectric effect support Planck’s quantum theory?
It showed light transfers energy in packets called photons.
Why does Bohr’s model fail for multi-electron atoms?
It cannot account for electron–electron interactions.
What does Heisenberg’s uncertainty principle state?
You cannot know both the exact position and the exact speed of an electron at the same time.