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History of Atomic Structure

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Presentation transcript:

Democritus- 5th Century philosopher from the Greek city of Abdera Student of Leucippus Conceived the idea of the “uncuttable”...the atom Democritus conceived of the Void as a vacuum, an infinite space in which moved an infinite number of atoms that made up Being (i.e. the physical world). These atoms are eternal and invisible; absolutely small, so small that their size cannot be diminished.

He claimed that there was no smallest part of matter and that different substances were made up of proportions of fire, air, earth, and water. As there were of course no experimental means available to test either view, Aristotle's prevailed mainly because people liked his philosophy better BC

John Dalton - English Published his “New System of Chemical Philosophy” whereby he championed the atomic theory. Gave several elements their symbols and arranged them in a table. Deduced that different elements have atoms of different mass.

Dalton's Atomic Theory 1) All matter is made of atoms. Atoms are indivisible and indestructible. 2) All atoms of a given element are identical in mass and properties 3) Compounds are formed by a combination of two or more different kinds of atoms. 4) A chemical reaction is a rearrangement of atoms.

J. J. Thomson - English Experimented with cathode ray tubes. Discovered rays were made of particles smaller than the atom. These negatively charged particles he called electrons. Thomson deduced that the atom was a positively charged ball with lots of electrons stuck into its surface.

Ernest Rutherford - New Zealand, England, & Canada Went to Cambridge to study with J.J. Thomson. In 1898 discovered particles he called alpha particles. By 1910, he had determined them to be positively charged protons occupying a central area of the atom. This, he postulated, was the atomic nucleus. Such a mon- umental discovery marked him as one of the greatest scientists of any age.

Neils Bohr…Denmark Student of Rutherford’s…1913 Perhaps I have found out a little about the structure of atoms. Don't talk about it to anyone, for otherwise I couldn't write to you about it so soon.... You understand that I may yet be wrong; for it hasn't been worked out fully yet (but I don't think its wrong).... Believe me, I am eager to finish it in a hurry, and to do so I have taken a couple of days off from the laboratory (this is also a secret).

Things are going rather well, for I believe I have found out a few things; but, to be sure, I have not been so quick to work them out as I was stupid to think. I hope to have a little paper ready and to show it to Rutherford before I leave, and I therefore am so busy, so busy. Bohr's theory that electrons existed in set orbits around the nucleus was the key to the periodic repetition of properties of the elements. The shells in which electrons orbit have different quantum numbers and hold only certain numbers of electrons -- the first shell holds no more than 2, the second shell up to 8, the third 10, the fourth 14.

“While working with Ernest Rutherford, Chadwick heard him speculating on the existence of a particle with no charge which sparked his interest. James performed experiments where he bombarded certain light elements with alpha particles leading to the discovery of a new type of particle, the neutron. For this,he won the Nobel Prize for physics in James Chadwick would die on July 14, 1974.” James Chadwick - England 1932

Electron Cloud Model Since electrons are travelling so fast, it is impossible to be able to detect where they are at any one time. Hence, the theory that they are constantly moving from level to level creating a cloud effect.

So…if opposite forces attract and like forces repel, and the nucleus of an atom is composed of neutrons and positively charged protons, why don’t the protons repel each other and blow the atom apart? What holds the protons together?