Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Democritus Going all the way back to the time of the Greek philosopher the idea of "stuff" was discussed. It was Democritus (460 370BC) that first proposed that materials were made up of indivisible, solid, homogeneous, and indestructible particles that they called atmos. Atmos in Greek means “that which cannot be further broken down into smaller pieces”. The size, shape, and movement of atoms determined the properties of matter (for example, liquids and solids). All matter was made of atoms which move through empty space. These atoms were described as the fundamental building block of all substances. Aristotle This theory was later refined by Aristotle who refuted the idea of atoms. Aristotle said that there can be no ultimately indivisible particles and empty space cannot exits. Instead, Aristotle used logic to derive a theory that matter was made of four elements: earth, air, water, and fire. This model was easily accepted by the public because it made sense to people. This caused the ideas of atoms to be driven underground for many centuries. Alchemists The “dark ages” of the atomic theory. Alchemy and superstition prevailed. Alchemists were able to isolate and identify some of today’s present elements such as sulfur and mercury. All knowledge gained in the area of chemistry was by accident as the goal of alchemy was to turn things into precious metals, such as gold. This was believed possible if they could discover the “philosopher’s stone”. Despite alchemists’ efforts, they were unsuccessful in turning cheap metals into gold. John Dalton The concept that small indivisible particles compose all matter was reawakened. Dalton built support for the particle theory through experimentation. In the first decade of the 1800's John Dalton created the modern atomic theory which had five major parts: 1. All matter is composed of small particles called atoms. 2. All atoms of a given element are identical. 3. Atoms cannot be created or destroyed or subdivided. 4. In chemical reactions, atoms combine with or separate from other atoms. 5. In chemical reactions, atoms combine with each other in simple whole number ratios to form combine atoms. Dalton also proposed the “Billiard Ball” Model which depicts atoms as solid and indivisible. J. J. Thomson In 1897 J.J. Thomson learned that atoms were divisible, he discovered that atoms could be broken down and one of those parts had a negative electrical charge, an electron. Thomson’s discovery countered Dalton’s atomic theory because it suggested there were particles smaller than the atom! Thompson discovered the first subatomic particle: the electron which has a negative charge! Thomson realizes the electron is part of the atom and that it leaves behind a positive mass when electrons are removed from an atom. Thomson constructs the “Plum Pudding” Model wherein electrons (negative) were randomly floating around in a "pudding" of positive charges. Ernest Rutherford Just over a decade later, Rutherford disproved Thomson’s “plum pudding” model. Instead Rutherford proposed that most of an atom’s mass and all of its positive charge are concentrated in a very small center called the nucleus. The electrons were seen to occupy a large volume of mostly empty space, but it wasn’t known how the electrons were arranged in that space. The discovery of the nucleus, its size and mass, was determined by pounding gold paper thin and shooting alpha particles through the gold foil. Rutherford found that some of the alpha particles were actually deflected by the gold foil, which means that there must be a positive charge in the center of an atom. Neil Bohr Though Rutherford's discoveries advanced atomic theory it left a gaping hole. Where were the electrons in the atom? In 1913 Niels Bohr theorized the planetary model of the atom. The nucleus was like the sun, situated in the center of the atom, and the electrons occupied orbits much like the planets. The orbits had certain energies and were specific distances from the nucleus. This model did a great job of explaining hydrogen, the simplest of atoms, but could not explain any other element on the periodic table. Despite its shortcomings, it was adopted and accepted for many years because no alternative model worked as well. Louis de Broglie: Broglie discovered that moving objects travel in waves, including electrons, so the path of an electron changed from circular (like the Bohr model) to elliptical. Werner Heisenberg: Heisenberg developed his uncertainty principle, which stated that it is impossible to know exactly where rapidly moving particles, like electrons, are at any single moment. One can only make guesses as to an electron’s probable position. Erwin Schrödinger: Combine de Broglie’s and Heisenberg’s findings into the development of the Schrodinger equation. This equation mathematically identifies the probability of the distance the electron would be found from the nucleus. You may know the direction of a particle for certain but speed then is unknown. Modern Theory: The current model used today is the Quantum Mechanical Model. Electrons occupy regions of space (orbitals) around the nucleus determined by their energies. Activity Create a summary of the information you were given using your own words. You should also research the contributor and find a couple more facts using the internet or your textbook. Evenly distribute the information between your group and be prepared to present your information. In your presentation you will include one drawing that best represents your person’s contribution to the structure of the atom. Also, you will create one or two sentences that best summarizes that person’s contribution to the atomic model. Mark Breakdown /5 Presentation /2 - Make sure you are not reading off your paper and you know the material. Summary /2 - Neatly type or write up the summary of the information you were given and hand it in. Make sure the information is in your own words. - Include your one or two sentences that best summarizes that person’s contribution to the atomic structure. Picture /1 - Include a picture that best describes the atomic model representation.