Mrs. Jiménez’s Abbreviated Version of Atomic History for Study Purposes
Scientist
Democritus
Dalton
Thomson
Rutherford
Main Discovery
Atoms are “indivisible”
Atomic Theory of Matter Proposed:
1 – All elements are composed of atoms
2 – All atoms of the same element are exactly alike
3 – Atoms of different elements are different (different mass)
4 – Compounds are made by joining two or more atoms of the same
or difference elements
Discovered electrons and that they are NEGATIVELY charged
subatomic particles in a neutral atom. Therefore, there must be some
positive and counteracting charge in the atom. He proposed the “plum
pudding model,” whereby electrons were moving about in a “sea” of
positive charge.
Dense, but small, positively charged and centrally located atomic
nucleus.
Most of the atom is empty space.
Chadwick
Bohr
Shrodinger
Discovered the neutrons, which exist so that positively charged protons
will not repel each other so as to explode out of the nucleus.
Proposed that electrons travel at fixed distances from the nucleus in an
atom such that they orbit the nucleus much like planets orbit the sun.
He also proposed ideas for how electrons could absorb energy to
become excited and then fall back to ground state configuration.
Proposed the cloud model of electron location probability. This
describes the likelihood of finding an electron in a given orbital.
Experiment/Model
Word “atomos” means indivisible in Greek
Atomic Theory of Matter
Cathode Ray Tube Experiment
- discovered that by passing an electric current, a
cathode ray beam would be created. This cathode ray
was attracted to a positive electrode and repelled by a
negative electrode, indicating that the cathode ray was
composed of tiny negative particles that he later called
electrons
Plum pudding model or Chocolate chip cookie model
Gold Foil Experiment
https://www.youtube.com/watch?v=_uEFKG122dA
-shot positively charged alpha particles at foil
containing gold atoms. Most passed right through
indicating that atoms are mostly empty space. A very
small amount were shot directly backwards because
they were repelled by the + nucleus.
1-5 Words
Indivisible
Atoms
Atomic Matter
Theory
Negative
Electrons, Plum
Pudding,
Positive Small
Nucleus, Gold
Foil
Neutrons
Planetary Model
Electrons in
Orbit, Planetary
Model
Electron Cloud Model
Electron Cloud
Model
BOHR’S PLANETARY MODEL