Ch 2. Atomic Structure

Ch 2. Atomic Structure

1. Ideas about Atoms

   • John Dalton (1808)
     • Atoms are indivisble and indestructible
     • The atoms of a given element are identical to each other and have the same mas and chemical properties
     • Atoms of different elements vary in mass
   • Joseph Thomson (Plum Pudding Model)
     • showed that cathode rays were attracted by the positive plate
       • this meant they had a negative charge

2. The Nucleus

   • Ernest Rutherford
     • Disproved Thomson's model of the atom
     • conducted the gold foil experiment
       • proved that the nucleus was mostly empty space
     • proposed that nearly all the mass of the atom is densely concentrated in a tiny central region called the nucleus
   • Niels Bohr (1913)
     • proposed electrons were arranged in a series of concentric circular orbits at an increasing distance around the nucleus

3. Definitions

   • The atomic number of an element is the number of protons in the nucleus of an atom of that element
   • The mass number of an atom is the sum of the number of protons and the number of neutrons in the nucleus
   • Isotopes are atoms with the same number of protons but different numbers of neutrons
   • The relative atomic mass of an element is the average mass of an atom of the element relative to one-twelfth the mass of an atom of carbon-12

4. Charges in a Atom

   • Neutrons (Neutral)
   • Protons (Positive)
   • Electrons (Negative)

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