Unit 1 Lesson 1: The Development Of The Atomic Model

Question 1

Democritus

Answer 1

Democritus theorized that particles get to a size where they can no longer be divided. He called these particles atomos, which means invisible.
This is where we get the name atoms
400 bc

Question 2

John Daltons

Answer 2

1809
Theorized that atoms are small spheres
Atoms of the same element are identical
Atoms cannot be destroyed or created
All matter consists of particles

Question 3

J.J. Thomson

Answer 3

1904
Used the cathode ray tube experiment to discover the presence of electrons
Further discovered the mass of an electron (1/2000 of a hydrogen atom)
He created the plum pudding model - positively charged mass with negative particles throughout it.

Question 4

Rutherford

Answer 4

Created the gold foil experiment and discovered the nucleus. He shot positively charged alpha particles at a thin gold foil and found that while most particles went through the foil a few particles were deflected.
The nuclear model - atoms are mostly empty space with a small dense positively charged nucleus with electrons orbiting the empty space around the nucleus.
Limitations:
Nucleus composed of positive charges should break apart due to repulsive force.
Could not explain the total mass of an atom.
Moving charges usually give off energy and thus the electrons should lose energy and crash into the nucleus, but this does not happen

Question 5

Bohr

Answer 5

1920
Spectral line experiment - high voltage connected to terminals of a tube containing hydrogen gas
When electricity hits an electron, it gives it some energy moving it further from the nucleus to an exited state
When the electron returns to its ground state it gives it an amount of energy which can sometimes be seen as a colour of visible light
Bohr’s atomic model - positively charged nucleus with electrons with electrons travelling around it in specific energy levels
“Quantized energy” - because energy is restricted to only certain discrete quantities