Atomic Theory Quiz
Questions: 16 · 10 minutes
1. A sealed container has the same total mass before and after a chemical reaction. Which historical principle does this observation illustrate?
Proust’s law of definite proportions
Bohr’s principle of quantized energy levels
Lavoisier’s law of conservation of mass
Heisenberg’s uncertainty principle
2. Why was Einstein’s explanation of Brownian motion historically important to atomic theory?
It demonstrated that electrons travel in fixed circular paths.
It provided quantitative support for the physical existence of atoms and molecules.
It established that nuclei contain protons and neutrons.
It proved that all atoms of one element have the same mass.
3. Which observation did Bohr’s model explain more successfully than Rutherford’s nuclear model alone?
The existence of isotopes with different masses
The deflection of cathode rays by electric fields
The discrete lines in hydrogen’s emission spectrum
The spontaneous decay of unstable nuclei
4. Which description best matches Thomson’s “plum pudding” model of the atom?
A dense positive nucleus surrounded by mostly empty space
A neutral nucleus surrounded by standing electron waves
Negative electrons embedded within a diffuse region of positive charge
An indivisible solid sphere with no smaller components
5. A student draws electrons as tiny objects following exact circular tracks around a nucleus. What is the main correction offered by the modern quantum model?
Electrons are located inside protons rather than outside the nucleus.
Electron locations are described by probability distributions called orbitals, not exact classical paths.
Electrons remain motionless at fixed points around the nucleus.
Electron energies vary continuously with no allowed levels or patterns.
6. Two atoms of the same element react chemically in nearly identical ways but have different masses. Which statement from Dalton’s original theory requires modification to account for them?
Matter is composed of atoms.
Compounds form when atoms of different elements combine.
Chemical reactions rearrange atoms.
All atoms of a given element have identical masses and properties.
7. Henry Moseley showed that elements are ordered more fundamentally by atomic number than by atomic mass. What does atomic number represent?
The combined number of protons and neutrons
The number of protons in the nucleus
The number of occupied electron shells
The average mass of an element’s isotopes
8. Which discovery resulted from J. J. Thomson’s experiments with cathode rays?
Atoms contain negatively charged particles called electrons.
The nucleus contains neutral particles called neutrons.
Electrons behave only as waves and never as particles.
Positive charge is concentrated in a tiny nucleus.
9. How did Democritus’s contribution differ from the later atomic theory proposed by Dalton?
Democritus measured atomic masses, while Dalton demonstrated radioactivity.
Democritus discovered electrons, while Dalton discovered protons.
Democritus described a nuclear atom, while Dalton proposed electron shells.
Democritus offered a philosophical idea, while Dalton built a scientific theory connected to experimental evidence.
10. In Rutherford’s gold-foil experiment, most alpha particles passed through the foil, but a small number were sharply deflected. What conclusion best fits both observations?
Electrons are embedded uniformly throughout a positively charged sphere.
Atoms are solid, indivisible particles with no internal structure.
An atom is mostly empty space with a small, dense, positive nucleus.
The nucleus fills most of the atom and has a negative charge.
11. An excited hydrogen atom releases light at only certain wavelengths rather than across a continuous range. How did Bohr interpret this?
Electrons emit photons when moving between specific allowed energy levels.
Electrons can possess any energy but emit only selected colors.
Atoms contain no empty space between the nucleus and electrons.
The nucleus emits light whenever a proton changes into a neutron.
12. A cathode ray bends toward a positively charged plate and away from a negatively charged plate. What can be inferred about the ray?
It consists of electrically neutral particles.
It is produced only by the atomic nucleus.
It consists of positively charged particles.
It consists of negatively charged particles.
13. Suppose nearly every alpha particle in Rutherford’s experiment had rebounded from the gold foil. Which atomic structure would that result have suggested instead?
Positive charge exists only in electrons outside the atom.
The atom has no concentrated matter or charge anywhere.
Electrons and protons have exactly the same mass.
Dense matter occupies much more of the atom’s volume than Rutherford concluded.
14. Which particle did James Chadwick identify through experiments involving radiation produced when beryllium was bombarded with alpha particles?
Electron
Neutron
Positron
Proton
15. A chemist finds that two elements form one compound in a 1:1 mass ratio and another in a 1:2 mass ratio. Which part of Dalton’s theory best explains this pattern?
Atoms combine in simple whole-number ratios to form compounds.
Electrons occupy only fixed energy levels around the nucleus.
Atoms contain equal numbers of protons and neutrons.
Atomic nuclei can change identity through radioactive decay.
16. A pure sample of water always contains hydrogen and oxygen in the same proportion by mass. Which law does this demonstrate?
The law of definite proportions
The law of multiple proportions
The law of conservation of energy
The periodic law