An atomic theory is a model developed to explain the properties and behaviors of atoms. As with any scientific theory, an atomic theory is based on scientific evidence available at any provided time and serves to suggest future lines of studies about atoms. The concept of an atom should be traced to debates atom structure that took location around the sixth 100 years B. One regarding the questions that interested these thinkers was the nature of matter. They used to ask, Is reason continuous or discontinuous? That is, whether you should break apart a piece of chalk as long as you wanted, should you ever reach some ultimate particle beyond which distant division was impossible? Or should you hold up that process of division forever? A proponent regarding the ultimate particle concept was the philosopher Democritus c.
, who named those particles atomos from the Greek, atomos that means indivisible. The debate over ultimate particles, however, was not ever resolved. Greek philosophers had no interest in testing their plans with experiments. They preferred to decide those concepts that were most sound logically. For higher than 2,000 years, the Democritus concept of atoms languished as kind of a secondary interest between scientists.
Then, within first decade regarding the 1800s, the plan was revived. English chemist Peter Dalton 17661844 proposed first modern atomic theory. Dalton's theory should be called modern due to the fact that it contained statements about atoms that should be tested experimentally. Dalton's theory had 5 primary points as stated below: All reason is composed of very tiny particles called atoms. All atoms of a provided element are identical.
Atoms cannot be created, destroyed, or subdivided. In chemical reactions, atoms combine with or separate from other atoms. In chemical reactions, atoms combine with each other in simple, whole-number ratios to shape combined atoms. By the term combined atoms, Dalton meant the particles that we now call molecules. Dalton's atomic theory is important not due to the fact that everything he spoke about was correct.
Instead, its price lies within the studies plans it contains. As each component of Dalton's theory was tested, new plans about atoms were discovered. For example, in 1897, English physicist J. Thomson 18561940 discovered that atoms are not indivisible. When excited by means of an electrical current, atoms break below into 3 parts.
two of those components is a tiny particle carrying a negative electrical charge, the electron. To explain what he had discovered, Thomson suggested an special model regarding the atom, a model widely known as the plum-pudding atom. The name returns from a comparison regarding the atom with a general English plum pudding, in which plums are embedded in pudding. In Thomson's atomic model, the plums are negatively charged electrons, and the pudding is a mass of positive charge. Like the Dalton model prior to it, Thomson's plum pudding atom was soon place to test.
It did not survive very long. Within the period between 1906 and 1908, English chemist and physicist Ernest Rutherford studied the effects of bombarding thin gold foil with alpha particles. alpha particles are helium atoms that have lost their electrons and, hence, are positively charged. Rutherford reasoned that the method alpha particles traveled through the gold foil should release him facts related to the structure of gold atoms within the foil. Rutherford's experiments provided him with 3 important pieces of information.
First, most regarding the alpha particles traveled right through the foil without being deflected at all. From this result Rutherford concluded that atoms consist mostly of empty space. Second, a little regarding the alpha particles were deflected at very sharp angles. In fact, some reflected completely backwards and were detected next to gun from which they were first produced. Rutherford was enormously surprised.
The result, he said, was something like shooting a cannon ball at a piece of tissue cardboard and possessing the ball bounce return at you. Regarding to Rutherford, the conclusion to be drawn from this result was that the positive charge in an atom should all be packed together in one tiny region regarding the atom. He called that region the nucleus regarding the atom. A sketch of Rutherford's nuclear atom is shown within the figure as well. One component of Rutherford's model, the nucleus, has turned out to be correct.
However, his placement of electrons created some problems, which he himself recognized. The peculiar difficulty is that electrons cannot remain stationary in an atom, as they appear to be. If they were stationary, they should be attracted to nucleus and grow to component of it as electrons are negatively charged and the nucleus is positively charged and opposite charges attract each other. But the electrons should not be spinning around the nucleus either. Regarding to a well-known law of physics, charged particles like electrons that venture through space release off energy.
Moving electrons should eventually lose energy, lose speed, and fall into the nucleus. Electrons in Rutherford's atom should neither be at rest nor in motion. The solution to this dilemma was proposed in an special and brilliant atomic theory in 1913. Suppose, spoke about Danish physicist Niels Bohr 18851962, that locations exist within the atom where electrons can venture without losing energy. Let us call those locations permitted orbits, something like the orbits that planets venture in their journey around the Sun.
If we can accept that idea, Bohr said, the challenge with electrons in Rutherford's atom should be solved. Scientists were flabbergasted. Bohr was saying that the method to explain the structure of an atom was to ignore an accepted principle of physics, at fewest for sure tiny components regarding the atom. The Bohr model sounded almost like cheating: inventing a model just due to the fact that it may look right. The test, of course, was to look if the Bohr model should survive experiments drafted specifically to test it.
Within a very brief period of time, other scientists were can report that the Bohr model met all the tests they were can devise for it. By 1930, then, the accepted model regarding the atom consisted of 3 parts, a nucleus whose positive charge was known to be due to tiny particles called protons, and one or more electrons arranged in distinct orbits outside the nucleus. One final challenge remained. Within the Bohr model, there should be an equal many protons and electrons. This balance is the only method to be sure that an atom is electrically neutral, which we have knowledge of to be the case for all atoms.
But if one adds up the mass total no. of reason of all the protons and electrons in an atom, the total returns no where near the actual mass of an atom. The solution to this challenge was suggested by English physicist James Chadwick in 1932. The reason for mass differences, Chadwick found, was that the nuclei of atoms contain a particle with no electric charge. He called this particle a neutron.
Chadwick's discovery resulted in a model regarding the atom that is fairly easy to understand. The core regarding the atom is the atomic nucleus, in which are located one or more protons and neutrons. Outside the nucleus are electrons traveling in discrete orbits. While this model regarding the atom should be used to explain many regarding the plans in chemistry in which ordinary people are interested, the model has not been used by chemists themselves for many decades. The reason for this difference is that revolutionary changes occurred in physics during the 1920s.
These changes included the rise of relativity, quantum theory, and uncertainty that forced chemists to rethink the highest many simple concepts about atoms. As an example, the principle of uncertainty says that it is impossible to describe with done accuracy most the position and the motion of an object. In other words, one may be can speak very accurately where an electron is located in an atom, but this reduces the accuracy with which we can describe its motion. By the end regarding the 1920s, then, chemists had begun to look for new ways to describe the atom that should incorporate the new discoveries in physics. One step in this direction was to rely fewer on physical models and more on mathematical models.
That is, chemists began to release up on the plan of an electron like a tiny particle carrying an electrical charge traveling in a sure direction with a sure velocity in a sure component of an atom. Instead, they began to look for mathematical equations which, when solved, gave the correct answers for the charge, mass, speed, spin, and other properties regarding the electron. Mathematical models regarding the atom are many times very difficult to understand, but they can be enormously useful and successful for professional chemists. The clues they have provided related to the ultimate structure of reason have led not only to an improved understanding of atoms themselves, but also to development of countless innovative new products in our daily lives. One regarding the highest many remarkable features of atomic theory is that even today, subsequent to hundreds of years of research, no one has yet seen a lone atom.
Some regarding the very greatest microscopes have produced images of groups of atoms, but no actual picture of an atom yet exists. How, then, can scientists be so confidently sure regarding the existence of atoms and regarding the models they have created for them? The answer is that models regarding the atom, like other scientific models, should be tested by experimentation. Those models that pass the test of experimentation survive, while those that do not are abandoned. The model of atoms that scientists use currently has survived and been modified by untold numbers of experiments and should be subjected to other such tests within the future.
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