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Evidence of the existence of atoms

Ditulis oleh : Dodo Pujakesuma Jumat, Agustus 05, 2011
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When Dalton proposed the atomic theory, theory attracted considerable attention. However, this theory failed to get full support. Some supporters of Dalton makes a variety of important efforts to persuade the fight against this theory, but some opposition still exists. Chemistry was not enough to prove the existence of atoms with the experiments. So the atomic theory remains a hypothesis. Furthermore, science after the 18th century developed a variety of experiments that make many scientists became skeptical of the atomic hypothesis. For example, like the famous chemist Sir Humphry Davy (1778-1829) and Michael Faraday (1791-1867), both from England, both doubt on the theory of atoms.

While the atomic theory remains a hypothesis, a variety of great progress in various fields of science blinded. One is the rapid emergence of thermodynamics in the 19th century. Structural chemistry was represented by the atomic theory is only a matter of academic with little possibility of practical application. But the thermodynamics derived from practical issues such as efficiency of steam engines seem more important. There is a very sharp controversy between the atomic with the support of thermodynamics. The debate between Austrian physicist Ludwig Boltzmann (1844-1906) and the German chemist Friedrich Wilhelm Ostwald (1853-1932) with the Austrian physicist Ernst Mach (1838-1916) is noteworthy. This debate is bad, Boltzmann committed suicide.

In the early 20th century, there were major changes in the interest of science. A series of important discoveries, including radioactivity, causing interest in the properties of atoms, and more generally, structural science. That there are atoms in the experiment were confirmed by sedimentation equilibrium experiments by Perrin.

English botanist, Robert Brown (1773-1858) discovered the irregular motion of colloidal particles and the motion is called motion Brow, in his honor. Swiss physicist Albert Einstein (1879-1955) developed a theory based on the theory of atomic motion. According to this theory, Brownian motion can be expressed by an equation that contains Avogadro's number.

D =(RT/N).(1/6παη) (1.1)

D is the motion of particles, R the gas constant, T the temperature, N Avogadro's number, α particle radius and η the viscosity of the solution.

Perrin's core idea is as follows. Colloidal particles move randomly by Brownian motion and simultaneously settle down by the influence of gravity. Equilibrium sedimentation equilibrium generated by these two motion, random motion and sedimentation. Perrin carefully observe the distribution of colloidal particles, and with the help of equation 1.1 and its data, he got the Avogadro's number. Surprising value acquired by Avogadro's number matched those obtained with other methods are different. This further proves a match for the theory of atoms on which to base the theory of Brownian motion.

No need to mention, Perrin could not observe atoms directly. What can a scientist at that time, including Perrin, is to show that Avogadro's number obtained from a number of different methods based on the theory of identical atoms. In other words they prove the theory of atoms indirectly with logical consistency.

Within the framework of modern chemistry, such methodology is still important. Even to this day is still not possible to directly observe the particles as small as atoms with the naked eye or microscope optics. To observe directly with visible light, the particle size must be greater than the wavelength of visible light. The wavelength of visible light is in the range of 4,0 x 10-7- 7,0 x10-7 m, the magnitude of 1000 times larger than the size of an atom. So clearly outside the range of optical devices to observe the atom. With the help of new tools such as electron microscopy (EM) or scanning tunneling microscope (STM), this impossibility can be overcome. Although the principle of observing the atom with this tool, in contrast to what is involved with observing the moon or a flower, we can say that we can now observe atoms directly.

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Dalton's Atomic Theory

Ditulis oleh : Dodo Pujakesuma Senin, Agustus 01, 2011
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At the beginning of the 19th century, the atomic theory of matter as a philosophy has been well developed by Dalton who developed the atomic theory based on the role of atoms in chemical reactions. Atomic theory is summarized as follows:

Dalton's atomic theory:

  1. elementary particles that make up the elements are atoms. All the atoms of certain elements are identical.
  2. the atomic mass of the same type will be identical but different from the atomic mass of elements of other types.
  3. all atoms involved in chemical reactions. Whole atom will form a compound. The type and number of atoms in certain compounds remain.
Theoretical basis of Dalton's theory is mainly based on the law of conservation of mass and comparative law remains. Both have been found previously, and multiple comparisons of law developed by Dalton himself.

  • Certain compounds always contain the same element mass ratio.
  • When two elements A and B form a series of compounds, the mass ratio of B which reacts with a number of A can be reduced to simple integers.
Democritos atoms can be considered as a kind of miniature material. So the number of types of atoms will be equal to the amount of material. On the other hand, Dalton is a constituent atom of matter, and many compounds can be formed by a limited number of atoms. So, there will be a limited number of types of atoms. Dalton's atomic theory of the process requires two or more atoms combine to form matter. This is the reason why the atomic chemistry Dalton called atoms.

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Ancient Atomic Theory

Ditulis oleh : Dodo Pujakesuma Minggu, Juli 31, 2011
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As noted earlier, the roots of modern chemistry is the atomic theory developed by the ancient Greek philosopher. Atomic philosophy of ancient Greece is often associated with Democritos (approximately 460BC-approximately 370 BC). However, no writing Democritos living. Therefore, we must be the source of the long poem "De rerum natura" by artist Roman Lucretius (about 96 BC-about 55 BC).

Presented by Lucretius atom has similarities with modern molecules. Grapes (wine) and olive oil, for example, have the atoms themselves. Atom is an abstract entity. Atom has a distinctive form with function in accordance with the shape. "Atomic wine is round and smooth so it can pass through the esophagus with smooth and rough while the atoms of quinine would be difficult through the esophagus." Modern structural theory of molecular states that there is a very close relationship between molecular structure and function.

Although the philosophy articulated by Lucretius is not supported by evidence obtained from experiments, this is the beginning of modern chemistry.

In the long period since the ancient times to the medieval theory of the atom remains In heretikal (berlwanan with the generally accepted theory) because the theory of four elements (water, soil, air and fire) proposed Aristotoles ancient Greek philosopher (384 BC-322 BC) in charge. When otortas Aristotle began to decline in early modern centuries, many philosophers and scientists began to develop theories that influenced the Greek atomic theory. Preview the material retained by the French philosopher Rene Descartes (1596-1650), German philosopher Gottfried Wilhelm Freiherr von Leibniz (1646-1716), and the English scientist Sir Isaac Newton (1642-1727) who more or less influenced by the atomic theory.

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At the beginning of The Birth of Chemistry

Ditulis oleh : Dodo Pujakesuma Jumat, Juli 22, 2011
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Modern chemistry initiated by the French chemist Antoine Laurent Lavoisier (1743-1794). He discovered the law of conservation of mass in chemical reactions, and uncover the role of oxygen in combustion. Based on this principle, advanced chemistry in the right direction.

Oxygen actually discovered independently by two chemists, English chemist Joseph Priestley (1733-1804) and Swedish chemist Carl Wilhelm Scheele (1742-1786), at the end of the 18th century. Thus, only about two hundred years before the birth of modern chemistry. Thus, chemistry is a science is relatively young when compared to physics and mathematics, both have developed several thousand years.

However, alchemy, metallurgy and pharmacy in antiquity can be regarded as the root chemistry. Many discoveries found by people actively involved in these areas contribute greatly to modern chemistry, although alchemy was based on a wrong theory. Furthermore, before the 18th century, metallurgical and pharmaceutical actually based on experience alone and not a theory. So, it seems unlikely these starting points that evolved into modern chemistry. Based on these things and the nature of modern chemistry is well organized and systematic methodology, real roots of modern chemistry may be found in ancient Greek philosophy.

The road from the ancient Greek philosophy to modern atomic theory is not always smooth. In ancient Greece, there is sharp disagreement between the atomic theory and the denial of the existence of atoms. Actually, the atomic theory remains unorthodox in the world of chemistry and science. Educated people are not interested in atomic theory until the 18th century. At the beginning of the 19th century, the English chemist John Dalton (1766-1844) gave birth to the ancient Greek atomic theory re. Even after the rebirth of this, not all scientists accept the theory of atoms. Not until the early 20th century theory of ato, finally proven as fact, not just hypothetical. This is achieved by a skilled trial by the French chemist Jean Baptiste Perrin (1870-1942). So, it took long enough to establish the basis of modern chemistry.

To Be Continue...

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