Atomic Theory

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Questions and Answers

Who proposed the concept of atoms in the 5th century BCE?

Ernest Rutherford
J.J. Thomson
Democritus (correct)
John Dalton

What was John Dalton's major contribution to atomic theory?

Discovery of the electron
Modern atomic theory formulation (correct)
Nuclear model of the atom
Quantized energy levels

What does the plum pudding model, proposed by J.J. Thomson, depict?

Electrons embedded in a positively charged cloud (correct)
Atoms combining in fixed ratios
Electrons orbiting a nucleus
Atoms as indivisible particles

What did Ernest Rutherford's gold foil experiment reveal?

Atoms consist of a dense nucleus surrounded by electrons (D)

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Which atomic theory principle states that atoms cannot be created or destroyed in chemical reactions?

Conservation of mass (A)

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In which year did John Dalton publish his atomic theory?

1808 (A)

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What model did Niels Bohr introduce regarding atomic structure?

Bohr model with quantized energy levels (B)

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Which scientist is credited with the discovery of electrons?

J.J. Thomson (A)

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Which of the following statements is NOT a part of Dalton's atomic theory?

Atoms can be divided into smaller particles (A)

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What philosophical idea regarding atoms did Leucippus and Democritus propose?

Atoms are eternal and unchangeable (D)

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Flashcards

A scientific framework explaining matter's nature, based on discrete units called atoms.

Democritus

Ancient Greek philosopher who proposed the idea of atoms as indivisible particles.

Dalton's Atomic Theory

19th-century theory stating all matter is made of atoms, atoms of an element are identical, and atoms combine in fixed ratios in compounds.

Plum Pudding Model

J.J. Thomson's model of the atom, picturing electrons embedded within a positive charge.

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Nuclear Model

Rutherford's model describing the atom with a small, dense nucleus containing positive charge and electrons orbiting it.

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Bohr Model

Niels Bohr's model adding quantized energy levels to the atom, where electrons orbit at specific energy levels.

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Atom

The smallest unit of an element that retains its chemical properties.

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John Dalton

19th-century British scientist credited with modern atomic theory.

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J.J. Thomson

Scientist credited with discovering the electron and the plum pudding model.

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Ernest Rutherford

Scientist who proposed the nuclear model of the atom.

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Study Notes

Atomic Theory - Key Concepts

Atomic theories explain matter's nature and behavior through discrete units called atoms. These theories evolved from philosophical speculation to rigorous scientific models.

Historical Development

Ancient Greek philosophers Leucippus and Democritus (5th century BCE) proposed the concept of atoms as indivisible, fundamental particles.
John Dalton (1808) formulated the modern atomic theory, based on experimental evidence. Key principles included:
- All matter is comprised of atoms.
- Atoms of the same element have identical properties and masses.
- Atoms are neither created nor destroyed during chemical reactions.
- Compounds form when atoms of different elements combine in fixed ratios.

Advancements in Atomic Theory

J.J. Thomson (1897): Discovered electrons and proposed the "plum pudding" model, suggesting electrons are embedded within a positively charged substance.
Ernest Rutherford (1911): Gold foil experiment revealed a small, dense nucleus at the atom's center, surrounded by electrons. This led to the nuclear model.
Niels Bohr (1913): Developed the Bohr model, introducing quantized energy levels for electrons.

Summary of Key Discoveries

Scientist	Contribution	Year
Democritus	Proposed the concept of atoms	5th century BCE
John Dalton	Formulated modern atomic theory	1808
J.J. Thomson	Discovered electrons, plum pudding model	1897
Ernest Rutherford	Nuclear model of the atom	1911
Niels Bohr	Bohr model with quantized energy levels	1913

Modern Atomic Theory

The modern approach to atomic theory is largely based on experimental observations and established models.
Dalton's theory built upon verifiable observations to establish the key principles of how atoms function and interact.

Conclusion

Atomic theories have transformed significantly from philosophical ideas to a detailed scientific understanding. Many scientists have contributed to this understanding, and it forms the foundation of chemistry and physics today.