Model #1 Solid Sphere: John Dalton              

Characteristics:

 

1.              All elements are composed of indivisible, indestructible particles (atoms).

2.              All atoms of an element are identical – especially by mass

3.              Atoms of different elements are different – especially in mass

4.              Atoms of 1 element cannot be changed into another

5.              Compounds are made from joining two or more atoms.

 

Factors that caused:

 

1.           Lavoisier’s  “Law of Conservation of Matter” showed that the mass of the products was equal to the mass of the reactants.

2.           Proust’s “Law of Definite Proportions” showed that the proportion by mass of elements in a compound is always the same.

 

 


Model #2  Raisin Bun/Plum Pudding J.J. Thomson

Characteristics:

 

1.              The atom is a solid mass of positive charge

2.           There are many negative particles evenly spaced inside

 

 

Factors that caused:

 

1.              Crookes and Thomson developed the cathode-ray tube and discovered that cathode rays were streams of negative particles (electrons).

 

2.           Millikan conducted the oil drop experiment and determined the charge on an electron and that all electrons are identical.

 


Model # 3  Nuclear: Ernest Rutherford

Characteristics:

 

1.    Most of the atom is empty space where the electrons are found.

2.    Most of the mass of the atoms is located in a small, positive area called the nucleus.

 

 

Factors that caused:

 

1.    Radioactivity was discovered, including alpha, beta, and gamma types.

 

2.    Rutherford conducted his gold foil experiment in which gold foil was bombarded by alpha particles. Most passed through, but some were deflected.

 

Model # 4  Planetary/Solar: Niels Bohr


Characteristics:

 


1.              There are certain, definite orbits in which electrons can be found.

2.           The greater the radius of the orbit, the more energy an electron has.

3.           The only way an electron can lose energy is to move from a greater radius (higher energy level) to a lower.

4.           As long as electrons stay in their orbits, they cannot lose energy.

5.           Electrons already in the lowest orbit (ground state) cannot loose energy.

 

Factors that caused:

 

1.              Scientists observe that elements produce bright line spectra.

2.              Planck proposed that light has wave properties but is made of bundles of energy called photons.

Model #5  Electron Cloud/Quantum Mechanical: Heisenberg,

 deBroglie, Shroedinger


Characteristics:

 


1.    Only the probable location of an electron can be estimated

2.    The region of high probability is represented as a cloud of negative charge (electron cloud)

3.    Highest probability is in a dense area near the nucleus.

 

 

Factors that caused:

 

1.    deBroglie proposes that matter can have wave-like properties

2.    Wave (Quantum) mechanic equations were developed to explain the motion of subatomic particles