Atom Timeline

Question 1

First Subatomic Particle Discovered

Answer 1

Electron (1897)

Question 2

Second Subatomic Particle Discovered

Answer 2

Proton (1919, named 1920)

Question 3

Third Subatomic Particle Discovered

Answer 3

Neutron (1932)

Question 4

First Atomic Model

Answer 4

John Dalton’s Sphere Model
- All objects are made of particles called atoms, and they are solid spheres that cannot be divided further into smaller particles.

Question 5

Second Atom Model

Answer 5

J.J. Thomson’s Plum Pudding Model
- experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons.
- Thomson proposed the plum pudding model of the atom, which had negatively-charged electrons embedded within a positively-charged “soup.” Like a cookie, where the atom is the cookie and the electrons are the cohocolate chips

Question 6

Third Atomic Model

Answer 6

Ernest Rutherford’s Nuclear Model
- In the nuclear atom, the protons and neutrons, which comprise nearly all of the mass of the atom, are located in the nucleus at the center of the atom.

Question 7

Fourth Atomic Model

Answer 7

Neils Bohr’s Planetary Model
- electrons are arranged in concentric circular orbits around the nucleus. (representing the solar system)

Question 8

Fifth Atomic Model

Answer 8

Erwin Schrödinger’s Quantum Mechanical Model
- Describes the probability of finding electrons within given orbitals, or three-dimensional regions of space, within an atom.
- Electrons reside inside of a cloud of energy, rather than set orbitals