Catalyst IN YOUR JOURNAL!1. What are the two subatomic particles found in the nucleus?2. What is the charge of a proton? An electron?3. How do you survive the zombie apocalypse?
End
Design an Experiment
• With your table:– Design an experiment
to distinguish humans from zombies in the video.
– Make sure to talk about how you will collect data and make a hypothesis for the experiment that you are about to run.
Connection to Atomic Theory
• What we know about the atom was discovered through scientific experiments.
• Without these experiments we would not be able to have our current model of the atom.
Today’s Learning Targets
• LT 1.2 – I can explain the development of atomic theory incorporating the contributions of Dalton, Thomson, Rutherford, and Bohr.
Outline of Thomson’s Experiment
• Attached battery to cathode tube, saw beam form.
• Beam contained subatomic particles.• Put a positive magnet next to the beam
and it bent towards the magnet.• Put a negative magnet next to the beam
and it bent away from the magnet.
Thomson’s Discovery
• Thomson discovered the electron!• He discovered that atoms must contain
some negatively charged particles, which he called electrons.
• Tells us nothing about the location of the electron within the atom.
Plum Pudding Model
• Thompson proposed that electrons were balls of negative charge floating in a sea of positive charges.
A Picture Says a 1000 Words
• With your table, make a drawing of Thomson’s experiment.
• Label the major components (cathode ray tube, magnets, etc.)
• Provide a brief explanation of how this led to the discovery of the electron and the plum pudding model of the atom.
• Be prepared to present your creation.
Ernest Rutherford
• Student of Thomson.• Disproved Plum
Pudding Model with Gold Foil Experiment
• Used alpha particles, which are small, positively charged particles.
Rutherford’s Experiment
• Shot positively charged alpha particles at a piece of gold foil.
• Most particles went straight through the foil.
• Small amount of the particles were deflected, but still went through
• An even smaller amount were bounced back
Justify – TPS
• Using Rutherford’s data below, make a hypothesis about what this data indicates.
Observations Proportion
Particles went straight through the foil
>98%
Particles went through foil, but were deflected at an angle
2%
Particles bounced off the gold foil 0.01%
Rutherford noted: “It was almost as if you fired a 15-inch shell into a piece of tissue
paper and it came back and hit you.”
What Rutherford’s Data Meant
• Most alpha particles went straight through because the atom is mostly empty space.
• Some alpha particles deflected because they came close to the electrons.
• The few alpha particles that bounced back were hitting the very small, but very dense positively charged nucleus.
Important Point #1
• The atom is mostly empty space. This is why most of the alpha particles went through
• The majority of the atom does not have anything in it.
Important Point #2
• The atom has very small, but very dense nucleus.
• Alpha particles that bounced back were coming into contact with nucleus.
• Alpha particles were deflected back because nucleus is positive.
What Bohr Knew
• Shooting electricity through the hydrogen excited electrons, which produced colors.
• Color produced only for specific values• Problem – If electrons were free to roam,
then we should get all sorts of colors…
Bohr’s Solution
• Electrons are restricted to orbitals or energy levels; they are not free to roam the electron cloud!
The Modern Model
electron
neutron
proton
Rutherford’s space and nucleus
Dalton’s atom
Bohr’s energy levels
Thompson’s electrons
Question 2
• What was the instrument called that J.J. Thomson used in his experiment to discover the electron?
Question 7
• When Bohr looked at the hydrogen lamp through his special equipment, what was the name of the spectrum of light he saw?
Rate Yourself
• Based on the exit ticket and your current level of understanding, rate yourself 1 – 4 on LT 1.2