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A short history of the knowledge of the atom Compiled by Jim Walker Latest revision: A unit of matter, the smallest unit of an element, consisting of a dense, central, positively charged nucleus surrounded by a system of electrons, equal in number to the number of nuclear protons, the entire structure having an approximate diameter of centimeter and characteristically remaining undivided in chemical reactions except for limited removal, transfer, or exchange of certain electrons.
The history of the study of the atomic nature of matter illustrates the thinking process that goes on in the philosophers and scientists heads. The models they use do not provide an absolute understanding of the atom but only a way of abstracting so that they can make useful predictions about them.
The epistemological methods that scientists use provide us with the best known way of arriving at useful science and factual knowledge. No other method has yet proven as successful.
In the beginning Actually, the thought about electricity came before atoms. In about B. Thales of Miletus discovered that a piece of amber, after rubbing it with fur, attracts bits of hair and feathers and other light objects.
He suggested that this mysterious force came from the amber. Thales, however, did not connect this force with any atomic particle.
Not until around B. He asked this question: If you break a piece of matter in half, and then break it in half again, how many breaks will you have to make before you can break it no further?
Democritus thought that it ended at some point, a smallest possible bit of matter. He called these basic matter particles, atoms. Unfortunately, the atomic ideas of Democritus had no lasting effects on other Greek philosophers, including Aristotle. In fact, Aristotle dismissed the atomic idea as worthless.
Primates have great mimicking ability. For more than years nobody did anything to continue the explorations that the Greeks had started into the nature of matter. Although he did not know about their structure, he knew that the evidence pointed to something fundamental.
Thomson discovered the electron and proposed a model for the structure of the atom. Thomson knew that electrons had a negative charge and thought that matter must have a positive charge.
His model looked like raisins stuck on the surface of a lump of pudding. In Max Planck, a professor of theoretical physics in Berlin showed that when you vibrate atoms strong enough, such as when you heat an object until it glows, you can measure the energy only in discrete units.
He called these energy packets, quanta.
Physicists at the time thought that light consisted of waves but, according to Albert Einstein, the quanta behaved like discrete particles. InAlbert Einstein wrote a ground-breaking paper that explained that light absorption can release electrons from atoms, a phenomenon called the "photoelectric effect.
I anachronistically use the word photon here. Actually, physicists did not refer to light quanta as photons until after Gilbert N. Lewis proposed the name in an article in Nature, VolPt. A heated controversy occured for many years on deciding whether light consisted of waves or particles.
The evidence appeared strong for both cases.
Later, physicists showed that light appears as either wave-like or particle-like but never both at the same time depending on the experimental setup. Other particles got discovered around this time called alpha rays. These particles had a positive charge and physicists thought that they consisted of the positive parts of the Thompson atom now known as the nucleus of atoms.
In Ernest Rutherford thought it would prove interesting to bombard atoms with these alpha rays, figuring that this experiment could investigate the inside of the atom sort of like a probe. He used Radium as the source of the alpha particles and shinned them onto the atoms in gold foil.
Behind the foil sat a fluorescent screen for which he could observe the alpha particles impact. The results of the experiments came unexpected. Most of the alpha particles went smoothly through the foil.
Only an occasional alpha veered sharply from its original path, sometimes bouncing straight back from the foil!Atoms are far too small to see directly, even with the most powerful optical microscopes. But atoms do interact with and under some circumstances emit light in ways that reveal their internal structures in amazingly fine detail.
ATOMS (A short history of the knowledge of the atom) Compiled by Jim Walker. Originated: Sept. Latest revision: Nov. atom n. A unit of matter, the smallest unit of an element, consisting of a dense, central, positively charged nucleus surrounded by a system of electrons, equal in number to the number of nuclear protons, the entire structure having an approximate diameter of Chapter 2: Atoms and the Periodic Table This content can also be downloaded as an printable PDF, adobe reader is required for full functionality.
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