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Unit 2
Chp. 3
Atoms: The smallest particle of an element that retains the chemical properties of that element.
Law of conservation of mass: Mass can neither be destroyed or created under ordinary conditions.
Discovery of e-
    Cathode ray tube observations
Object placed at the opposite end of the tube cast a shadow on the glass.
Paddle wheel moved along the rails.
A negatively charged magnet deflected Rays.
Thomson: Measured ratio of the charge of a particle to its mass.
          Electrons have a very large charge for their mass.
Millikan: redefined Thomson's work to get the exact mass of the electron by using the oil drop experiment.
Atomic Structure
Atom: the smallest particle of an element that retains the chemical properties of that element.
Atomic Structure:
      Proton: Positively charged particle   p+
      Neutron: Neutrally charged particle  no
   Energy levels
      Electron: Negatively charged particle  e-  (smallest particle makes up the greatest amount of space)
General atomic information
   Atoms are electrically neutral (same number of protons and electrons)
   Nuclei of different elements differ in the number of p+. The atomic number gives the element its identity
   Nuclear forces: Strong short ranges forces between p-p, p-n, n-n.
Discovery of nucleus: Rutherford Gold Foil Experiment
Counting atoms
Atomic number (Z) the number of p+ in the nucleus**Periodic table is arranged by increasing atomic number.

Interactive periodic table

Ex:        12 g   + 16 g   = 28 g

Law of multiple proportions:  If two or more different compounds are composed of the same two elements, the masses of the second element combine with a certain mass of the first element can be expressed as ratios of small whole numbers.


Law of definite composition:  Whatever mass units are used and no matter how much of a compound you have or where it came from the mass ratio will always be the same.


Daltons Atomic theory  vs. Modern atomic theory
Dalton said all atoms of the same element were identical.-----The modern atomic theory says we have isotopes and all atoms are not the same
Dalton said atoms could not be broken down into smaller parts.----------The modern atomic theory says atoms are composed of three subatomic particles.