ATOMIC THEORY CHEM
DH PRACTICE TEST 79
QUESTIONS
Question 1: Which statement best describes Democritus's contribution to atomic
theory?
Choices:
1) He proposed that matter consists of tiny indivisible particles based mainly on philosophical reasoning.2) He measured the charge of the electron with oil drops.3) He discovered the neutron through beryllium experiments.4) He proved that electrons occupy quantized energy levels.Correct Answer: He proposed that matter consists of tiny indivisible particles based mainly on philosophical reasoning.Explanation: Democritus proposed that matter is made of tiny particles often called atomos.His proposal was philosophical rather than based on controlled experiments.Page 1
Question 2: Why is John Dalton's work considered a foundation of modern atomic
theory?
Choices:
1) He directly imaged individual atoms with an electron microscope.2) He used experimental chemical evidence to formulate a testable theory of atoms and whole-number combining ratios.3) He discovered the nucleus by scattering alpha particles.4) He introduced electron orbitals from the Schrödinger equation.Correct Answer: He used experimental chemical evidence to formulate a testable theory of atoms and whole-number combining ratios.Explanation: Dalton connected atomic ideas to experimental laws of chemical combination and proposed that compounds form from atoms in simple whole-number ratios.
Question 3: Which observation is most consistent with Dalton's law-based atomic
theory?
Choices:
1) Electrons can display wave-particle duality.2) Some nuclei spontaneously emit alpha particles.3) A given compound contains its constituent elements in a �xed ratio by mass.4) Atomic spectra consist of discrete lines.Correct Answer: A given compound contains its constituent elements in a �xed ratio by mass.Explanation: The law of de�nite proportions helped support Dalton's view that compounds contain �xed combinations of atoms, producing constant elemental mass ratios.Page 2
Question 4: Which part of Dalton's original atomic theory is known to be incorrect today?
Choices:
1) Matter is composed of atoms.2) Chemical reactions rearrange atoms.3) Compounds can form from atoms in whole-number ratios.4) All atoms of a given element are identical in mass.
Correct Answer: All atoms of a given element are identical in mass.
Explanation: Isotopes show that atoms of the same element can have di�erent masses because they contain di�erent numbers of neutrons.
Question 5: What did J. J. Thomson's cathode-ray experiments demonstrate?
Choices:
1) Cathode rays contain negatively charged particles that are components of atoms.2) Atoms contain a tiny positively charged nucleus.3) Neutrons have nearly the same mass as protons.4) Electrons can occupy only integer principal energy levels.Correct Answer: Cathode rays contain negatively charged particles that are components of atoms.Explanation: Thomson showed that cathode rays were streams of negatively charged particles, later called electrons, establishing that atoms are divisible.Page 3