1. The Evolution of the Atomic Model

2. Dalton’s Atomic Model – Early 1800s
The atom is a small, hard, indestructible ______________.
All atoms of the same _______________ are identical in __________ and __________.
Atoms of different elements are different in _____________ and ___________.
________________ ____________

3. Thomson’s Atomic Model – 1897
About 100 years later...
Discovered the existence of ________________ charged particles.
These particles are now called _____________.
Electrons were the first ____________________ particles to be discovered and studied.
Thomson’s Atomic Model:
Negatively (-) charged electrons embedded in a (+) charged mass.
Also known as the “Raisin Bun” model.

4. Rutherford’s Atomic Model – 1898
Rutherford was Thomson’s student!
Watch
Rutherford’s Gold Foil Experiment
Radioactive substance was placed in a __________ _________ and emitted (+) charged particles called ____________ ____________.
Through a pinhole in the box, these particles were “shot” at a thin piece of ___________ _____________.
Prediction:
Based off of Thomson’s Model, which is mostly _____________ ______________.
Most, if not all, of the particles would ____________________________________________________________ ____________________________________________________________.

5. Results:
Most alpha particles went _________ _________ the foil.
Some alpha particles ___________________.
Some alpha particles __________ ____________.
Explanation:
Atom must be made mostly of _____________ ___________.
Atom must have _________, ____________ charged ____________. He called this the _______________.

6. BUT WAIT....
If the nucleus is positively charged, and electrons are negatively charged, shouldn’t they attract each other?
Shouldn’t the electrons just end up spiralling into the nucleus?!

7. Bohr & Energy Levels
Determined that there are only a few levels in which electrons can exist.
Proposed the idea existence of the atomic energy level.
Electrons can jump from a lower level to a higher level when they ________ a ____________ of energy (electric current, spark, heat, or light).
Electrons can drop from a higher level to a lower level when they ________ a ____________ of energy (released in the form of light).
Electrons can not exist in between the allowed energy levels.

8. James Chadwick
Eventually, after many years of work by several scientists, the positive charge in the nucleus was caused by subatomic particles that they called _________________.
Scientific evidence indicated there was more than just one type of particle in the nucleus.
For example, Rutherford knew that the mass of the nucleus was more than the mass of the protons alone.
James Chadwick (a former co-worker of Rutherford’s), showed experimentally that neutral particles, now called _____________, help make up the nuclei of most atoms.

9. Bohr-Rutherford Model Diagrams
Has a central positive ________________ and electrons in _____________ levels around the nucleus.
There have been additional changes and refinements to our understanding of the atom, but this model is very useful to help understand the structure of the atom.

10. Atomic Model Summary Briefly describe each model, and sketch a diagram below each description.
Dalton
Thomson
Rutherford
Bohr-Rutherford