by A.D.
Timeline of the Evolution of the Atomic Model:
Greeks Dalton Thomson Rutherford Bohr Wave
Greek Concept of Atoms
Democritus and Leucuppius
Two Greek scientists that helped understand this theory were Leucuppius and Democritus.
The word atom comes from the Greek word "atomos" which means smallest unit of matter.
The scientists came up with the theory:
1.)That everything is composed of atoms
2.)All atoms are different in size, shape, and possibly weight
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Atoms are all different |
Dalton's Atomic Theory
John Dalton, Early 1800's
Elements consists of tiny particles (atoms)
All atoms are identical.
All atoms have the same mass
Different atoms of different elements are different
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Explains that all atoms are same, yet are different for each element |
Thomson's Atomic Model
Joseph John (J.J.) Thompson, 1987
Spherical shape with a positive charge
The volume of this sphere is embedded with electrons which have a negative charge
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| Atom has a positive charge with electrons embedded within it. |
Rutherford's Atomic Model
Ernest Rutherford, 1911
Positive charge in the nucleus
Electrons scattered around the nucleus
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| Shows that the nucleus has a positive charge with electrons floating around it |
Experiment:
Shot a beam of positively chared alpha particles at gold foil
Particles went through foil
Some bounced back
Came to the conclusion that the positively charged alpha particles bounced off the gold foil because the mass of the neucleus was positively charged. Two positve charges repel each other.
-Proved that mass is positively charged in a nucleus
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| Most particles went through but some bounced back |
Bohr's Atomic Model
Neils Bhor, 1913
Electrons move in circular orbits around atom's nucleus
Only certain orbits are permitted around the nucleus
When atoms absorb energy, electrons can move to different orbits, yet they release photon which have electromagnetic energy
Light of certain colors can be created when the electrons change orbits
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| Shows positive nucleus with negatively charged electrons going in orbits around it |
Wave Model
Schrodinger, 1925
This theory is a part of Quantom Physics
Atoms with the highest atomic number are unstable and break down into smaller waves
Describes that there is no exact place to find an electron within the orbit and hence a probabilty factor is involved in calculating the location of an electron at a particular moment
Atoms don't have orbits, but orbitals of certain energies
[FrontPage Image Map Component]
Common Sense Science. 2002. Common Sense Science. 9 Mar. 2003 <http://www.commonsensescience.org/index.htm?atoms-r.htm~main>.
Drews, K. "Friends School Chemistry" 07 Apr. 2003 <http://www.bcpl.net/~kdrews/mtas/modern3.html#Wave>
