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Questions and Answers
Which of the following statements accurately reflects John Dalton's atomic theory?
Which of the following statements accurately reflects John Dalton's atomic theory?
What did Empedocles propose was the composition of all matter?
What did Empedocles propose was the composition of all matter?
Which philosopher's ideas led to the decline of the atomic view of matter for centuries?
Which philosopher's ideas led to the decline of the atomic view of matter for centuries?
What scientific device did Sir William Crookes invent to study electrical discharge?
What scientific device did Sir William Crookes invent to study electrical discharge?
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What term did Johnstone G. Stoney use to describe the fundamental unit carrying electricity?
What term did Johnstone G. Stoney use to describe the fundamental unit carrying electricity?
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What significant value did J.J. Thomson calculate regarding cathode rays?
What significant value did J.J. Thomson calculate regarding cathode rays?
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Which property indicates that cathode rays possess kinetic energy?
Which property indicates that cathode rays possess kinetic energy?
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What happens when an electric field is applied to cathode rays?
What happens when an electric field is applied to cathode rays?
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What was a common misconception about the nature of cathode rays during J.J. Thomson's time?
What was a common misconception about the nature of cathode rays during J.J. Thomson's time?
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Which experimental result supported the particle theory of cathode rays?
Which experimental result supported the particle theory of cathode rays?
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Study Notes
Ancient Philosophical Views on Matter
- Early speculations about fundamental components of the world date back to philosophers such as Empedocles (~440 BC), who proposed four elements: earth, fire, air, and water.
- Hindus similarly recognized these four elements as constitutive of the universe and space.
- Democritus (460–370 BC) introduced the concept of ‘atomos’, envisioning the material world as composed of tiny, indivisible particles.
Shift in Philosophical Thought
- Plato and Aristotle dismissed the idea of indivisible particles, leading to the decline of atomic theory during the dominance of Aristotelean philosophy for centuries.
Dalton's Atomic Theory
- In 1808, John Dalton articulated a clear definition of atoms, asserting:
- Elements consist of extremely small, indivisible particles known as atoms.
- All atoms of a given element are identical in mass and size, differing from atoms of other elements.
- Atoms of one element cannot convert into atoms of another element through chemical reactions; atoms are conserved in reactions.
- Compounds form through the union of two or more atoms from different elements in simple numerical ratios.
- Dalton's model is referred to as the "Golf ball model."
Discovery of Electrons
- Johnstone G. Stoney (1826-1911) coined the term “electrons” in 1891, although lacking experimental evidence.
Cathode Ray Experimentation
- Sir William Crookes invented the cathode ray tube in the mid-1800s to investigate electrical discharge in a vacuum.
- When high voltage is applied, the cathode (negatively charged plate) emits a stream of unseen radiation known as cathode rays, causing low-pressure gases to glow.
Properties of Cathode Rays
- Cathode rays travel in straight lines, as proven by the formation of sharp-edged shadows when opaque objects obstruct their path.
- They exhibit mass and possess kinetic energy; a light paddle wheel placed in their path will rotate, indicating momentum (though heating effects might influence this).
- Application of an electric field results in the deflection of cathode rays toward positive plates, confirming their negative charge. Their trajectory in a magnetic field aligns with that of other negatively charged particles.
J.J. Thomson's Contributions
- J.J. Thomson (1856–1940) established that cathode rays are identical regardless of the cathode material and gas used in the tube.
- In 1897, he described cathode rays as streams of negatively charged particles and calculated the electron's charge-to-mass ratio at 1.76 x 10^8 coulombs per gram.
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Description
Explore the ideas of early philosophers like Empedocles and Democritus, who significantly contributed to our understanding of the fundamental components of the world. This quiz delves into their beliefs regarding the elements and the concept of atoms, comparing Eastern and Western philosophies on matter.
