History of the Atom

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Questions and Answers

Which concept, introduced by Democritus, remains a fundamental principle in modern chemistry?

The four elements: earth, fire, air, and water.
Atoms having uniform sizes.
The indivisibility of atoms.
The existence of atoms. (correct)

How did Aristotle's view of matter differ significantly from that of Democritus?

Aristotle rejected the existence of atoms, proposing four fundamental elements instead. (correct)
Aristotle proposed that all matter was composed of atoms with varying sizes.
Aristotle believed in atoms moving in constant motion, while Democritus did not.
Aristotle thought energy was released when atoms released light when jumping from orbit, while Democritus did not.

Which statement accurately describes Dalton's atomic theory?

All matter is composed of indivisible particles called atoms. (correct)
Atoms can be created or destroyed during chemical reactions.
Atoms of the same element have different properties.
Atoms of different elements are identical in their properties.

What key discovery is attributed to J.J. Thomson's experiments?

The presence of electrons within atoms. (A) Signup and view all the answers

How did Rutherford's gold foil experiment change the understanding of atomic structure?

It showed atoms have a tiny positive charged nucleus. (A) Signup and view all the answers

Why was Rutherford's postulation of the neutron significant, even before its experimental discovery?

It accounted for the mass deficiency in the atomic nucleus. (B) Signup and view all the answers

What was James Chadwick's primary contribution to atomic theory?

Confirming the existence of neutrons. (A) Signup and view all the answers

How did Thomson's model of the atom differ from Rutherford's model?

Thomson viewed the atom as a uniform sphere of positive charge with embedded electrons, while Rutherford proposed a concentrated positive charge. (B) Signup and view all the answers

According to atomic theory, what happens to atoms during a chemical reaction?

Atoms are rearranged to form new substances. (A) Signup and view all the answers

Why did some alpha particles deflect at large angles in Rutherford's gold foil experiment?

Because the alpha particles encountered a concentrated positive charge in the nucleus. (B) Signup and view all the answers

How did Bohr incorporate the concept of energy levels into the atomic model?

He proposed electrons orbit the nucleus in specific energy levels, and can jump between them. (D) Signup and view all the answers

What limitation in Dalton's atomic theory was addressed by later discoveries?

The notion that atoms of the same element are identical. (D) Signup and view all the answers

Why was the discovery of isotopes important for refining the understanding of atomic structure?

It demonstrated that atoms of the same element can have different masses. (A) Signup and view all the answers

How does the concept of quantized energy levels explain the emission spectra of elements?

Electrons emit only specific energies when transitioning between quantized energy levels. (B) Signup and view all the answers

What role did empty space play in Rutherford's interpretation of the gold foil experiment?

It explained why most alpha particles passed through with little to no deflection. (A) Signup and view all the answers

What evidence supports the claim that electrons further from the nucleus have more energy?

Electrons closer to the nucleus require more energy to remove. (A) Signup and view all the answers

How does the concept of 'constant motion' as described by Democritus relate to modern physics?

It reflects the perpetual motion of particles at the atomic level, although understood differently. (B) Signup and view all the answers

Which of the following best explains why atoms of different elements have different properties according to Dalton's theory?

Atoms of different elements have different sizes and masses. (D) Signup and view all the answers

What experimental evidence led Rutherford to conclude that most of an atom’s mass is concentrated in the nucleus?

The observation that most alpha particles passed through the gold foil with little or no deflection, but some were deflected at large angles. (A) Signup and view all the answers

How did the concept of 'empty space' evolve from Democritus to Rutherford?

Democritus proposed the existence of empty space between atoms, while Rutherford demonstrated that atoms themselves are mostly empty space. (B) Signup and view all the answers

Flashcards

Democritus's Idea of Atoms

Indivisible and exist. They have different sizes, empty space and are in constant motion.

Dalton's Atomic Theory

All matter is made of atoms; same element = same atoms, different element = different atoms. Atoms are never created or destroyed, just rearranged during reactions.

Thomson's Atomic Model

Atoms have electrons, are neutral, and the rest of the atom is positive with electrons evenly distributed.

Rutherford's Model of the Atom

The center of an atom has a positively charged nucleus, occupies little space but has most of the mass, and is surrounded by electrons.