QCM : Fundamentals of Atomic Structure and Models — 11 questions

Questions et réponses du QCM

1. Which statement best describes Dalton’s contribution to atomic theory in 1808?

He described atoms as a sphere of positive charge with embedded electrons
He discovered that atoms contain shells labeled K, L, M, and N
He showed that positive charge is concentrated in a tiny nucleus
He proposed a scientific atomic theory based on experimental evidence available at the time

He proposed a scientific atomic theory based on experimental evidence available at the time

Explication

Dalton’s 1808 theory was the first scientific atomic theory based on experiments available then, treating atoms as indivisible building blocks. The other options describe later models by Thomson, Rutherford, and Bohr.

2. What are parmanus in ancient Indian thought and how do they differ from atomos in Greek philosophy?

Parmanus are infinitely small particles proposed in Indian philosophy, while atomos are indivisible particles in Greek philosophy.
Parmanus are theoretical particles in modern physics, while atomos are ancient philosophical ideas.
Both parmanus and atomos refer to indivisible particles, but parmanus are larger and observable.
Parmanus are indivisible particles in Greek philosophy, whereas atomos are infinitely small particles in Indian philosophy.

Parmanus are infinitely small particles proposed in Indian philosophy, while atomos are indivisible particles in Greek philosophy.

Explication

Parmanus are proposed as infinitely small particles in Indian philosophy, whereas atomos are the Greek concept of indivisible particles. The key difference is their cultural origin and the extent of their divisibility concept.

3. What is the main idea behind the ancient Greek concept of atomos?

Matter consists of a tiny dense nucleus with most of the atom empty space
Matter is stable only when electrons occupy fixed circular shells
Matter is made of electrons embedded in a uniform positive sphere
Matter is made of indivisible particles that are the basic constituents of substances

Matter is made of indivisible particles that are the basic constituents of substances

Explication

Atomos referred to indivisible particles proposed by ancient Greek thinkers as the basic constituents of matter. The other choices describe later atomic models or concepts.

4. Who proposed the concept of 'parmanus' as the smallest particles in ancient Indian philosophy?

Parmanus
Aristotle
Democritus
Plato

Parmanus

Explication

Parmanus were proposed in ancient Indian thought as the smallest, indivisible particles, distinct from Greek atomos. The other options are Greek philosophers or unrelated figures.

5. Why did Thomson place positive charge throughout the atom in his plum pudding model?

To explain why alpha particles bounce straight back from gold foil
To show that all atomic mass is concentrated in a nucleus
To balance the negative electrons and keep the atom electrically neutral
To allow electrons to move only in fixed stationary states

To balance the negative electrons and keep the atom electrically neutral

Explication

Thomson’s model had a uniform positive sphere with electrons embedded in it so the total positive and negative charges would balance. This was meant to preserve overall neutrality, not to explain nuclear scattering or Bohr-style shells.

6. What is the primary purpose of Rutherford’s gold foil experiment in understanding atomic structure?

To demonstrate that atoms are indivisible particles
To observe the behavior of electrons in fixed energy levels
To determine the size and concentration of the atomic nucleus
To test the validity of Thomson’s plum pudding model

To determine the size and concentration of the atomic nucleus

Explication

Rutherford’s experiment aimed to show that positive charge is concentrated in a tiny nucleus, which was evidenced by the large deflections of some alpha particles, contradicting Thomson’s model.

7. What did Thomson’s plum pudding model predict for an incoming alpha particle passing through matter?

It would be reflected by a tiny dense nucleus at the center
It would orbit in fixed shells without losing energy
It would pass through with only slight deflection because positive charge is spread evenly
It would combine with electrons to form neutral clusters

It would pass through with only slight deflection because positive charge is spread evenly

Explication

If positive charge is spread evenly through the atom, an alpha particle should pass mostly straight through with only slight deflection. Large-angle deflections and backscattering were not expected in Thomson’s model.

8. When did Niels Bohr propose his atomic model based on electrons moving in fixed circular orbits?

1906
1922
1932
1913

1913

Explication

Niels Bohr proposed his atomic model in 1913, introducing the concept of electrons moving in fixed energy levels or shells.

9. How does Bohr’s concept of stationary states differ from Rutherford’s nuclear model in explaining electron behavior?

Bohr’s model describes electrons as particles that only absorb or emit energy when changing orbits, unlike Rutherford’s model which sees electrons as continuously moving.
Bohr’s model emphasizes the wave nature of electrons, contrasting Rutherford’s particle-based approach.
Bohr’s model proposes electrons move in fixed orbits with constant energy, while Rutherford’s model suggests electrons orbit randomly around a nucleus.
Bohr’s model states electrons are fixed in place, whereas Rutherford’s model allows electrons to move freely in the atom.

Bohr’s model proposes electrons move in fixed orbits with constant energy, while Rutherford’s model suggests electrons orbit randomly around a nucleus.

Explication

Bohr’s model introduces fixed circular orbits (stationary states) where electrons do not lose energy, unlike Rutherford’s model which does not specify electron paths and focuses on the nucleus and empty space.

10. Who is credited with discovering the neutron and explaining its role in atomic mass and nuclear stability?

Ernest Rutherford
John Dalton
James Chadwick
Niels Bohr

James Chadwick

Explication

James Chadwick is credited with discovering the neutron in 1932, which helped explain atomic mass and the stability of nuclei, especially in heavier elements. Rutherford and Bohr contributed to nuclear and atomic models, but Chadwick's discovery was pivotal for neutrons.

11. What is the primary effect of increasing the number of neutrons in a nucleus of a heavy atom like uranium?

It decreases the atomic mass, making the atom lighter.
It enhances nuclear stability by reducing proton-proton repulsion.
It increases the atomic number, changing the element.
It causes the atom to become an isotope of a different element.

It enhances nuclear stability by reducing proton-proton repulsion.

Explication

Adding neutrons increases the overall nuclear mass and helps to reduce proton-proton repulsion, thereby stabilizing the nucleus. It does not change the atomic number or element, which is determined by protons.

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Origins of atomic theory

Ancient Greek and Indian ideas evolved into Dalton’s scientific model.

Parmanus Origin

Ancient Indian indivisible particles

Thomson’s plum pudding model

Atom is a positive sphere with embedded electrons.

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