1. Atoms: Development of the Atomic Theory

2. Democritus
460 BC - Greek philosopher proposes the existence of the atom
He pounded materials until he made them into smaller and smaller parts
He called them atoma which is Greek for “indivisible”.
Berryman, S. (2010). Democritus. Retrieved from

3. Democritus His Theory: All atoms: Are small hard particles
Are made of a single material formed into different shapes and sizes
Are always moving, and they form different materials by joining together
Berryman, S. (2010). Democritus. Retrieved from

4. Solid Sphere Model or Bowling Ball Model Proposed by John Dalton
British chemist; elements combine in specific proportions to form compounds
Solid Sphere Model or Bowling Ball Model
Proposed by John Dalton

5. John Dalton His Theory:
All substances are made of atoms that cannot be created, divided, or destroyed.
Atoms join with other atoms to make new substances.
Atoms of the same element are exactly alike, and atoms of different elements are different in mass and size.
De Leon, N. (n.d.). Dalton's atomic theory. Retrieved from

6. Plum Pudding Model or Raisin Bun Model
J.J. Thomson
English chemist and physicist; discovered 1st subatomic particles
Plum Pudding Model or Raisin Bun Model
Proposed by J.J. Thomson

7. J.J. Thomson
His Theory:
Atoms contain negatively charged particles called electrons and positively charged matter.
Created a model to describe the atom as a sphere filled with positive matter with negative particles mixed in
Referred to it as the plum pudding model

8. Proposed by Ernest Rutherford
New Zealand physicist discovered the nucleus
Nuclear Model
Proposed by Ernest Rutherford

9. Ernest Rutherford His Theory:
Small, dense, positively charged particle present in nucleus called a proton
Electrons travel around the nucleus, but their exact places cannot be described.

10. Bohr Model or Planetary Model
Niels Bohr
Danish physicist; discovered energy levels
Bohr Model or Planetary Model
Proposed by Niels Bohr
Renjishino1. (Designer). (2010). Lithium element 3. [Web Graphic]. Retrieved from
Halfdan. (Designer). (2003). Stylised_lithium_atom. [Web Graphic]. Retrieved from

11. Niels Bohr
His Theory:
Electrons travel around the nucleus in definite paths and fixed distances.
Electrons can jump from one level to a path in another level.

12. Proposed by Erwin Schrodinger
Erwin Shrodinger
Austrian physicist; developed the electron cloud model
Electron Cloud Model
Proposed by Erwin Schrodinger
Furmanj. (Designer). (2008). Helium atom. [Web Graphic]. Retrieved from

13. Erwin Shrodinger His Theory:
The exact path of electrons cannot be predicted.
The region referred to as the electron cloud, is an area where electrons can likely be found.

14. James Chadwick 1932 - English physicist; discovered neutrons
His Theory:
Neutrons have no electrical charge.
Neutrons have a mass nearly equal to the mass of a proton.
Unit of measurement for subatomic particles is the atomic mass unit (amu).

15. Modern Theory of the Atom
Atoms are composed of three main subatomic particles: the electron, proton, and neutron.
Most of the mass of the atom is concentrated in the nucleus of the atom.

16. Modern Theory of the Atom
The protons and neutrons are located within the nucleus, while the electrons exist outside of the nucleus.
In stable atoms, the number of protons is equal to the number of electrons.

17. Modern Theory of the Atom
The type of atom is determined by the number of protons it has.
The number of protons in an atom is equal to the atomic number.

18. Modern Theory of the Atom
The sum of the number of protons and neutrons in a particular atom is called the atomic mass.
Valence electrons are the outermost electrons.