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- An temporary explanation of the facts
- observed. It can be tested.
- It is a statement of a relationship between
- phenomena. It states what
- A theory attempts an explanation of why something happens.
- Theories evolve with time to explain new facts as they are discovered.
- Systematic observations or measurements
- carried (preferably) under controlled conditions to test the validity of a
- General observations, that may depend heavily
- on the observer.
- Measurable data, that in general depends less
- of the observer and more of the instrumentation.
- What forms the material universe, occupies
- space and has mass.
- Has a definite and constant composition. Has
- physical and chemical properties.
- Combination of substances where the
- components retain their properties.
- Composition and properties of the mixture is
- the same throughout the sample
The composition is not uniform.
- This substance cannot be separated into
- simpler substances by chemical methods.
- Made of atoms of elements bound together in a
- fixed proportion.
Transition from solid to liquid is given by
the melting point.
Transition from liquid to gas
Direct transition from solid to gas is
possible under certain conditions.
- can be used to
- separate a mixture into its pure components.
- alters the
- composition or identity of the substance(s) involved.
- •Depend on the amount of sample under
•Do not depend on the amount of sample
Who first postulated the Atomic Theory?
Who gave a precise definition of atom, element and compound?
are composed of extremely small particles
- composed of atoms of
- more than one element
involve the rearrangement of atoms.
cathode ray tube
- used to observe
- radiation in a laboratory setting.
A high vacuum, a high
voltage difference between two plates
- the source of the
Who measured the
charge-to-mass ratio of the electron
J. J. Thomson
Who measured the
charge of the electron
R. A. Millikan
How was the mass of
the electron determined
- A combination of Thomson’s and Millikan’s results
- allowed to do that.
- rays are positively
- charged, massive.
- rays are electrons,
- similar behavior as the radiation from the cathode ray tube experiment.
- rays are not charged,
- but very energetic.