ACS GENERAL CHEMISTRY – HISTORY OF THE
ATOM STUDY GUIDE WITH PRACTICE
QUESTIONS, CORRECT ANSWERS (VERIFIED
ANSWERS) PLUS RATIONALES 2026 Q&A |
INSTANT DOWNLOAD PDF
1. Who proposed the first modern atomic theory based on experimental
evidence?
A. J.J. Thomson
B. John Dalton
C. Ernest Rutherford
D. Niels Bohr
CORRECT ANSWER: B — John Dalton
Rationale:
Dalton proposed that matter is made of indivisible atoms and that atoms of different elements
differ in mass and properties.
2. What was the main idea of Dalton’s atomic theory?
A. Atoms contain electrons and protons
B. Atoms are indivisible particles of matter
C. Atoms orbit the nucleus
D. Atoms have energy levels
CORRECT ANSWER: B — Atoms are indivisible particles of matter
Rationale:
Dalton described atoms as solid, indivisible spheres (later modified by modern discoveries).
3. Who discovered the electron using cathode ray experiments?
A. Rutherford
B. Bohr
C. J.J. Thomson
D. Chadwick
,CORRECT ANSWER: C — J.J. Thomson
Rationale:
Thomson identified negatively charged particles (electrons) in cathode ray tubes.
4. What was the main conclusion of Thomson’s plum pudding model?
A. Atoms are empty space
B. Electrons are embedded in a positive sphere
C. Nucleus contains all mass
D. Electrons orbit in fixed paths
CORRECT ANSWER: B — Electrons are embedded in a positive sphere
Rationale:
Thomson proposed a positively charged “soup” with electrons embedded inside.
5. Who performed the gold foil experiment?
A. Bohr
B. Rutherford
C. Dalton
D. Planck
CORRECT ANSWER: B — Rutherford
Rationale:
Rutherford’s experiment led to the discovery of the nucleus.
6. What was Rutherford’s main discovery?
A. Electrons
B. Neutrons
C. Dense, positively charged nucleus
D. Energy levels
CORRECT ANSWER: C — Dense, positively charged nucleus
Rationale:
Most alpha particles passed through, but some were deflected, indicating a dense nucleus.
, 7. What did Rutherford conclude about the atom’s structure?
A. Mass is evenly distributed
B. Atom is mostly empty space
C. Electrons are fixed in place
D. No nucleus exists
CORRECT ANSWER: B — Atom is mostly empty space
Rationale:
Most of the atom is empty space with a small dense nucleus.
8. Who introduced quantized electron energy levels?
A. Dalton
B. Bohr
C. Thomson
D. Rutherford
CORRECT ANSWER: B — Bohr
Rationale:
Bohr proposed electrons exist in fixed energy levels or orbits.
9. What happens when an electron absorbs energy according to Bohr’s model?
A. It falls into nucleus
B. It disappears
C. It moves to a higher energy level
D. It becomes a proton
CORRECT ANSWER: C — It moves to a higher energy level
Rationale:
Electrons jump to higher orbits when energy is absorbed.
10. Who discovered the neutron?
ATOM STUDY GUIDE WITH PRACTICE
QUESTIONS, CORRECT ANSWERS (VERIFIED
ANSWERS) PLUS RATIONALES 2026 Q&A |
INSTANT DOWNLOAD PDF
1. Who proposed the first modern atomic theory based on experimental
evidence?
A. J.J. Thomson
B. John Dalton
C. Ernest Rutherford
D. Niels Bohr
CORRECT ANSWER: B — John Dalton
Rationale:
Dalton proposed that matter is made of indivisible atoms and that atoms of different elements
differ in mass and properties.
2. What was the main idea of Dalton’s atomic theory?
A. Atoms contain electrons and protons
B. Atoms are indivisible particles of matter
C. Atoms orbit the nucleus
D. Atoms have energy levels
CORRECT ANSWER: B — Atoms are indivisible particles of matter
Rationale:
Dalton described atoms as solid, indivisible spheres (later modified by modern discoveries).
3. Who discovered the electron using cathode ray experiments?
A. Rutherford
B. Bohr
C. J.J. Thomson
D. Chadwick
,CORRECT ANSWER: C — J.J. Thomson
Rationale:
Thomson identified negatively charged particles (electrons) in cathode ray tubes.
4. What was the main conclusion of Thomson’s plum pudding model?
A. Atoms are empty space
B. Electrons are embedded in a positive sphere
C. Nucleus contains all mass
D. Electrons orbit in fixed paths
CORRECT ANSWER: B — Electrons are embedded in a positive sphere
Rationale:
Thomson proposed a positively charged “soup” with electrons embedded inside.
5. Who performed the gold foil experiment?
A. Bohr
B. Rutherford
C. Dalton
D. Planck
CORRECT ANSWER: B — Rutherford
Rationale:
Rutherford’s experiment led to the discovery of the nucleus.
6. What was Rutherford’s main discovery?
A. Electrons
B. Neutrons
C. Dense, positively charged nucleus
D. Energy levels
CORRECT ANSWER: C — Dense, positively charged nucleus
Rationale:
Most alpha particles passed through, but some were deflected, indicating a dense nucleus.
, 7. What did Rutherford conclude about the atom’s structure?
A. Mass is evenly distributed
B. Atom is mostly empty space
C. Electrons are fixed in place
D. No nucleus exists
CORRECT ANSWER: B — Atom is mostly empty space
Rationale:
Most of the atom is empty space with a small dense nucleus.
8. Who introduced quantized electron energy levels?
A. Dalton
B. Bohr
C. Thomson
D. Rutherford
CORRECT ANSWER: B — Bohr
Rationale:
Bohr proposed electrons exist in fixed energy levels or orbits.
9. What happens when an electron absorbs energy according to Bohr’s model?
A. It falls into nucleus
B. It disappears
C. It moves to a higher energy level
D. It becomes a proton
CORRECT ANSWER: C — It moves to a higher energy level
Rationale:
Electrons jump to higher orbits when energy is absorbed.
10. Who discovered the neutron?
