Periodic Table
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Evidence of the existence of atoms
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 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.
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
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:
Dalton's atomic theory:
- elementary particles that make up the elements are atoms. All the atoms of certain elements are identical.
- the atomic mass of the same type will be identical but different from the atomic mass of elements of other types.
- all atoms involved in chemical reactions. Whole atom will form a compound. The type and number of atoms in certain compounds remain.
- 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.
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