Atomic Theory: Virtual Tour
ANSWER KEY
Ancient Greece
What did Democritus say about atoms?
They were indivisible pieces that made up all matter.
What caused changes in matter, according to the ancient Greeks?
Changes in matter was caused by combinations of the atoms as they moved throughout the void.
What did Aristotle feel about the Greek's atomic theory?
He disagreed with the theory.
What did Aristotle think materials were made of?
He thought materials were made of air, water, earth and fire.
Dalton
What was Dalton's definition of an atom?
An indestructible, indivisible particle.
How did Dalton realize compounds had specific amounts of atoms?
He studied how gases behaved and noticed that the particles of gases changed depending on the combinations of gases.
What are the four components of Dalton's Theory?
1. Matter is made up of atoms that are indivisible and indestructible.
2. All atoms of an element are identical.
3. Atoms of different elements have different weights and different chemical properties.
4. Atoms of different elements combine in simple whole numbers to form compounds.
Thomson
What observation did Thomson make during the cathode-ray tube experiment?
Some of the rays were deflected – proving there was something in the atom causing them to be deflected in different directions.
What did Thomson discover?
The electron (in 1897)
What model of the atom did Thomson propose?
The plum-pudding model
Rutherford
What is the gold foil experiment?
Rutherford’s experiment where he shot rays of alpha particles through gold foil.
What did Rutherford see that proved Thomson wrong?
Some rays bounced straight back and some even went straight through. These results made him realize there was a dense nucleus and empty space as well.
What was Rutherford's change to the atomic model?
He made the “planetary model” where the electrons orbit a small, dense nucleus, like planets around the sun.
Bohr
How do electrons travel, according to Bohr?
They travel in orbits and can jump energy levels when they lose or gain energy.
How large is the nucleus, compared to the rest of the atom?
10,000 times smaller than the atom.
Explain the change from Rutherford's model to Bohr's model.
Instead of just orbiting, there are specific energy levels that the electrons can belong to. When they undergo chemical reactions, electrons can jump levels to bond.
Chadwick
What did Chadwick realize about the neutron?
The neutron was the same mass as a proton, but with no electrical charge – also inside the nucleus.
What did Chadwick notice that made him find/discover the neutron?
The fact that the atomic number did not equal the mass of the atom, which they thought it should as only protons were to be in the nucleus, where the mass was contained.
Modern Atomic Theory
How is the quantum mechanical model different from Bohr's Model?
The electrons do not travel in circular orbits, but differently shaped 3-D orbits depending on energy.
What does the Uncertainty Principle explain about the motion of the electrons?
That we cannot, for certain, pinpoint an electron in both time and space – we can only find one.