-
Hypothesis
- An temporary explanation of the facts
- observed. It can be tested.
-
Law
- It is a statement of a relationship between
- phenomena. It states what
- happens.
-
Theory
- A theory attempts an explanation of why something happens.
- Theories evolve with time to explain new facts as they are discovered.
-
Experiments
- Systematic observations or measurements
- carried (preferably) under controlled conditions to test the validity of a
- hypothesis.
-
Qualitative data
- General observations, that may depend heavily
- on the observer.
-
Quantitative data
- Measurable data, that in general depends less
- of the observer and more of the instrumentation.
-
Matter
- What forms the material universe, occupies
- space and has mass.
-
Substance
- Has a definite and constant composition. Has
- physical and chemical properties.
-
Mixture
- Combination of substances where the
- components retain their properties.
-
Homogeneous mixture
- Composition and properties of the mixture is
- the same throughout the sample
-
Heterogeneous mixture
The composition is not uniform.
-
Element
- This substance cannot be separated into
- simpler substances by chemical methods.
-
Compounds
- Made of atoms of elements bound together in a
- fixed proportion.
-
Transition from solid to liquid is given by
the melting point.
melting
-
Transition from liquid to gas
evaporation
-
Direct transition from solid to gas is
possible under certain conditions.
sublimation
-
Physical means
- can be used to
- separate a mixture into its pure components.
-
chemical change
- alters the
- composition or identity of the substance(s) involved.
-
Extensive Properties
- •Depend on the amount of sample under
- consideration
-
Intensive Properties
•Do not depend on the amount of sample
-
Who first postulated the Atomic Theory?
Democritus
-
Who gave a precise definition of atom, element and compound?
John Dalton
-
Elements
are composed of extremely small particles
atoms
-
Compounds
- composed of atoms of
- more than one element
-
Chemical reactions
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
-
cathode
- the source of the
- radiation
-
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.
-
Alpha
- rays are positively
- charged, massive.
-
Beta
- rays are electrons,
- similar behavior as the radiation from the cathode ray tube experiment.
-
Gamma
- rays are not charged,
- but very energetic.
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