www.Primo.com: Development of Atomic Theory.

1. John Dalton's Atomic Theory.

In 1803, John Dalton argued argued opinion about atoms. Dalton's atomic theory is based on two laws: the law of conservation of mass (Lavoisier law) and legal permanent arrangement (Prouts law). Voiced their Lavosier that "The total mass of the substances before the reaction will always be equal to the total mass of substances reaction products". While Prouts stated that "Comparison of mass elements in a compound always remain". The second law of Dalton point about the atom as follows:

Atom is the smallest part of the material that is not able to be subdivided
Atom is described as a very small solid ball, an element have identical atoms and different for different elements.
Atoms combine to form compounds with a ratio of integers and simple. For example, water is composed of hydrogen atoms and oxygen atoms
A chemical reaction is a separation or merger or rearrangement of atoms, so that the atoms can not be created or destroyed. Hypothesis Dalton's atomic model as depicted by solid ball as the shot put.

weaknesses:
Dalton theory does not explain the relationship between the solution of the compound and electric current conductivity.

2. Atomic Theory J. J. Thomson.

Based on the discovery of a better cathode tube by William Crookers, then JJ Thomson researching more on cathode rays and it is certain that the cathode rays are particles, because it can rotate the propeller is placed between the cathode and anode. From the results of this experiment, Thomson stated that the cathode rays are subatomic particles (subatomic particles) are negatively charged and hereinafter referred to as the electron.
Atoms are neutral particles, because negatively charged electrons, then there must be more positively charged particles to neutralize the negative charge of electron. From these findings, Thomson rectify the shortcomings of Dalton's atomic theory and atomic theory suggests that known as Thomson's Atomic Theory. Which states that:

"Atom is a solid ball of positively charged and negatively charged electrons scattered in it"

Atomic models can be described as cashews that have been exfoliated skin. describe the electrons are scattered evenly in the meat balls pink solid, which in Thomson's atomic model is analogous to a solid positive ball.

weaknesses:
Weakness Thomson atomic model can not explain the arrangement of positive and negative charges in the atomic sphere.

3. Rutherford Atomic Theory.

Rutherford along with two of his disciples (Hans Geigerdan Erners Masreden) conducted an experiment known as alpha ray scattering (λ) on thin plates of gold. Previously it has been found the presence of alpha particles, ie particles are positively charged and move straight, great penetrating power that can penetrate thin sheets of paper. The actual experiment aimed to test the opinion Thomson, namely whether the atom was really a solid ball which is positive when subjected to alpha particles would be reflected or deflected. From their observations, obtained the fact that if the alpha particle is fired at a very thin gold plate, then most of the alpha particles passed (no deviation angle of less than 1 °), but Marsden observations obtained from the fact that one in 20,000 alpha particles will turn angle of 90 even more.

Based on the symptoms that occur, obtained some conclusions few below:

Atom is not a solid ball, because almost all of the alpha particles passed
If the gold plate is considered as one of the gold layer of atoms, then the gold atom is very small particles are positively charged.
These particles build up the core particles, based on the fact that 1 in 20,000 alpha particles will be deflected. When the ratio of 1: 20,000 is the ratio of the diameter, core size obtained approximately 10,000 smaller than the overall size of the atom.
Based on facts obtained from these experiments, Rutherford proposed a model of the atom, known as the Rutherford Atomic Model states that atoms consist of a nucleus is very small and positively charged, surrounded by negatively charged electrons. Rutherford suspect that there are atoms in the core functions of neutral particles that bind positive particles that do not repel each other.

weaknesses:
Can not explain why the electrons do not fall into the nucleus.

4. Bohr Atomic Theory.

there in 1913, the Danish physicist Neils Bohr called Rutherford atom fix failures through experiments on the spectrum of the hydrogen atom. This experiment succeeded in providing a picture of the electrons to occupy the area around the atomic nucleus. Bohr's explanation of the hydrogen atom involves a combination of the classical theory of Rutherford and the quantum theory of Planck, expressed with four postulates, as follows:

There are only a certain set of orbits that allowed for an electron in a hydrogen atom. This orbit is known as the stationary state of motion (settled) electron and a circular path around the core.
During the electrons are in a stationary trajectory, the electron energy remains that there is no energy in the form of radiation emitted or absorbed.
Electrons can only move from one track to track other stationary stationary. In this transition, a certain amount of energy involved, the amount in accordance with Planck equation, ΔE = hv.
Stationary trajectory is allowed to have the scale with certain traits, especially the nature of the so-called angular momentum. The magnitude of the angular momentum is a multiple of h / 2Π or nh / 2Π, where n is an integer and h Planck constant.
According to the Bohr model of the atom, the electrons around the nucleus in certain trajectories called electron shells or energy levels. Lowest energy level is the electron shell which is located in, getting out of his skin and the greater the number the higher the energy level.

weaknesses:
The atomic model can not explain the color spectrum of many electron atoms.

5. Modern Atomic Theory.

Atomic model of quantum mechanics was developed by Erwin Schrodinger (1926). Before Erwin Schrodinger, an expert from the German Werner Heisenberg developed the theory of quantum mechanics known as the uncertainty principle is "not possible to determine the position and momentum of an object with caution at the same time, which can be determined is the probability of finding the electron at a given distance of the core ".

Region of space around the nucleus with a probability of getting called orbital electrons. Shape and orbital energy levels formulated by Erwin Schrodinger Schrodinger.Erwin solve an equation to obtain the wave function to describe the limits of the possible discovery of electrons in three dimensions.

Schrodinger equation.
x, y and z: Position in three dimensions
Y: The wave function
m: Mass
ђ: h / 2p where h = Plank's constant and p = 3.14
E: The total energy
V: The potential energy

Orbital model of the atom with the electron trajectory is called a model of modern atomic or quantum mechanical model of the atom which is valid until today, as seen in the picture below.

Electron cloud around the nucleus shows a probability of electrons. Describe the orbital energy levels of electrons. Orbitals with the same energy level or almost the same will form a sub skin. Some sub leather combine to form such kulit.Dengan skin consists of several sub-skin and consists of several orbital subshell. Although the position of the same skin but not necessarily the same orbital position.

Characteristic of the atomic model of wave mechanics.
The movement of electrons have wave properties, so the trajectory (orbit) is not stationary as the Bohr model, but after the completion of the squared wave functions are called orbitals (three-dimensional shape of the incident electron greatest invention to the particular circumstances in the atom).
The shape and size of the orbital depends on the price of three quantum numbers. (Electrons occupy orbital quantum number is expressed in)

The position of the electron as far as 0.529 Armstrong of core H according to Bohr instead of something definite, but a probable the biggest opportunity discovery of the electron. Thank you for reading this article.

Written and posted by Bambang Sunarno. sunarnobambang86@gmail.com

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DatePublished: January 14, 2015 at 10:47