atoms evolution

rom ancient Greece to the present era, models and theories of the atom continues to grow. Through the model and the theory of atoms, we can know the structure of an atom. These developments can not be separated from the efforts of scientists such as Democritus, John Dalton, JJ Thomson, Rutherford, Chadwick, Milikan, Niels Bohr, Schrodinger, de Broglie and Heisenberg.

1. Atomic theory of Democritus (460 BC-370 BC)
Democritus developed the theory about the composer in a material. According to Democritus, if a material constant of a split when it will obtain a fundamental particles called atoms (Greek: atomos = not divided). This opinion was rejected by Aristotle (384-322 BC), who argued that matter is continuous (the material can be split continuously until no finite). Aristotle further agree Empedokles theory, namely the material composed of fire, water, soil and air. Around the year 1592 - 1655 Gasendi proposed that atoms are the smallest part of a substance.

2. Dalton's Atomic Theory (1803)
John Dalton revealed that:
a. Atom is the smallest part of a substance.
b. Simple spherical atom is very small, can not be split, created or destroyed.
c. The same element contain the same atoms.
d. Similar atoms have the same properties in all respects, while the different atoms have different properties.
e. Chemical reactions occur because of the merger and separation of the atoms.
f. When the atoms are joined to form molecules. When the atoms are joined together to form molecules of elements, while if the atoms are joined to form different compounds.

Dalton's atomic theory Weakness
In further developments found several facts that can not be explained by the theory, among others:
a. Unable to explain the electrical properties of matter.
b. Unable to explain how atoms are bonded to each other.
c. Dalton atomic model can not explain the differences between atoms of one element with another element.

These weaknesses can be explained following the discovery of atomic particles compiler, such as the electron was discovered by Joseph John Thomson in 1900, the discovery of the proton beam by Goldstein in 1886.

Excess atomic theory Dalton
a. Can explain the Law of Conservation of Mass (Lavoisier law)
b. Can explain the Permanent Comparative Law (Law Proust)


3. Thomson's Atomic Theory
Based on experiments on electrical conductivity through a vacuum tube / tube pengawan charge (discharge tube) or cathode ray tube. In the cathode tube gas pressure in the tube can be arranged through the suction pump (vacuum pump). At sufficiently low pressure and high voltage (several thousand volts), the gas in the tube will be glowing with light whose color depends on the type of gas in the tube (gas neon red, yellow sodium gas). If the gas pressure is reduced, then the area in front of the cathode will be darkened. These dark areas will be increased if the gas pressure in the tube and hold reduced, eventually the whole tube becomes dark, but the front of the cathode fluorescent tube with a greenish color.

Through the experiment can be shown that perpendaran was caused by a radiation emanating from the surface of the cathode to the anode. Therefore, from the cathode, the radiation is called cathode rays. The experimental results prove that this cathode tubes are negatively charged particles in an atom because the rays can be deflected toward the positive pole of an electric field. This is the next cathode rays are negatively charged particles and by Thomson particles called electrons.