Title: LC Chemistry Notes 2023
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Markdown Content:
R. Gallagher www.theconical fl ask.ie
# The Atom
Dalton atomic theory:
1. All matter is made up of atoms.
2. All atoms are indivisible
Crookes discovered cathode rays .
# - Cathode rays are negatively charged beams of electrons.
Experiment 1: The Maltese cross
# - Results: Cathode rays produce a fl uoresce and travel in straight lines (produce a shadow).
# - Travel from the negative terminal of the battery towards the positive terminal.
Experiment 2: The paddle wheel
# - Results: Cathode rays have enough energy to cause the paddle wheel to move towards
positive terminal.
J.J Thompson discovered the electron
# - Result: Cathode rays are negative.
# - Discovered the charge to mass ratio of an electron.
# - His plum pudding model accounted for atoms being
electrically neutral but was overall incorrect.
# - Electrons are negatively charged sub-atomic particles.
Milikan: Oil drop experiment which discovered the charge on electron.
3R. Gallagher www.theconical fl ask.ie
Rutherford discovered the nucleus and proton
# - Rutherford bombarded a thin gold foil with alpha particles (positively charged particles).
Rutherford concluded:
Rutherford atomic structure:
Chadwick discovered the neutron
# - He bombarded beryllium with alpha particles however kept a para ffi n wax block behind the
apparatus.
# - He found that a neutral charged particle was hitting the para ffi n block.
# - Because neutrons are neutral (no charge) they were the most di ffi cult to detect.
Observation: Conclusion:
Most alpha particles pass straight through
the gold foil unde fl ected.
Most of the atom is empty space.
Some alpha particles are de fl ected at large
angles.
The alpha particles are repelled when they
pass a small and positive nucleus.
A tiny amount of alpha particles were
re fl ected straight back
The nucleus is very dense.
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