Atomic Theory Vocabulary, Models, and Scientists The Discovery of the Atom 440 B. C. to the present

This was Democritus’ atomic model. It was simply a round sphere with no electrons, protons, or neutrons. Democritus created the first atomic model. His contribution helped people with understanding the idea of an atom, and helped other scientists further look into the science of the atom and its generic makeup.

Dalton: 1803; All matter is composed of atoms (tiny indivisible particles)

Ernest Rutherford: English physicist proton A positively charged particle with a mass of 1 amu Located within the nucleus of the atom Ernest Rutherfor d, English physicist When: 1919

Ernest Rutherford-Born in New Zealand.Went to Cambridge in England where he lived and worked- 1919

John J. Thomson, British Scientist- 1897

J.J. Thomson- electron

Neutron-neutral- no charge neutron A neutral particle with a mass of 1 amu Located within the nucleus of the atom James Chadwick, English physicist When: 1935

Nucleus- protons and neutrons are here nucleus Small, dense, positively charged area Area located at the center of the atom Ernest Rutherford, English physicist When:

Murray Gell-Mann and George Zweig: American physicists: 1964 quark An extremely small particle found within a proton or neutron Located within the nucleus of the atom Murray Gell- MannMurray Gell- Mann and George Zweig, American physicists When: 1964

Gell-Mann and Zweig

Schrodinger (Austrian) and Heisenberg (German) 1926

Schrodinger (Austrian physicist) and Heisenberg (German physicist)- 1926

Schrodinger’s cat- a paradox Schrödinger's cat: a cat, a flask of poison, and a radioactive source are placed in a sealed box

The cat is not real! The cat does not get hurt! If an internal monitor detects radioactivity (i.e. a single atom decaying), the flask is shattered, releasing the poison that kills the cat

The Copenhagen interpretation of quantum mechanics implies that after a while, the cat is simultaneously alive and dead. Quantum mechanics is the study of the world of the very small…atoms. Rules are different.

The cat is not real! It doesn’t get hurt! Yet, when one looks in the box, one sees the cat alive or dead, not both alive and dead. This poses the question of when exactly quantum superposition ends and reality collapses into one possibility or the other.

A paradox is a statement that contradicts itself or a situation which seems to defy logic; contradiction. For example: Schrödinger’s Cat Paradox: A cat is in a box with a small amount of radioactive substance that could kill it. The cat could be either alive or dead while the box is closed; until someone opens the box to check, the cat exists in both states.

More explanation: A cat is placed in a steel box along with a Geiger counter, a vial of poison, a hammer, and a radioactive substance. When the radioactive substance decays, the Geiger detects it and triggers the hammer to release the poison, which subsequently kills the cat. The radioactive decay is a random process, and there is no way to predict when it will happen. Physicists say the atom exists in a state known as a superposition—both decayed and not decayed at the same time

The cat is not hurt; it is hypothetical Until the box is opened, an observer doesn't know whether the cat is alive or dead—because the cat's fate is intrinsically tied to whether or not the atom has decayed and the cat would, as Schrödinger put it, be "living and dead... in equal parts" until it is observed. In other words, until the box was opened, the cat's state is completely unknown and therefore, the cat is considered to be both alive and dead at the same time until it is observed.

A paradox is a statement that contradicts itself or a situation which seems to defy logic; contradiction. For example "If you put the cat in the box, and if there's no way of saying what the cat is doing, you have to treat it as if it's doing all of the possible things—being living and dead—at the same time," explains Eric Martell, an associate professor of physics and astronomy at Millikin University. "If you try to make predictions and you assume you know the status of the cat, you're [probably] going to be wrong. If, on the other hand, you assume it's in a combination of all of the possible states that it can be, you'll be correct."

Immediately upon looking at the cat, an observer would immediately know if the cat was alive or dead and the "superposition" of the cat—the idea that it was in both states—would collapse into either the knowledge that "the cat is alive" or "the cat is dead," but not both. Schrödinger developed the paradox, says Martell, to illustrate a point in quantum mechanics about the nature of wave particles.

"What we discovered in the late 1800s and early 1900s is that really, really tiny things didn't obey Newton's Laws," he says. "So the rules that we used to govern the motion of a ball or person or car couldn't be used to explain how an electron or atom works."

At the very heart of quantum theory—which is used to describe how subatomic particles like electrons and protons behave—is the idea of a wave function. A wave function describes all of the possible states that such particles can have, including properties like energy, momentum, and position.

The wave function is a combination of all of the possible wave functions that exist," says Martell. "A wave function for a particle says there's some probability that it can be in any allowed position. But you can't necessarily say you know that it's in a particular position without observing it. If you put an electron around the nucleus, it can have any of the allowed states or positions, unless we look at it and know where it is."

That's what Schrödinger was illustrating with the cat paradox, he says. "In any physical system, without observation, you cannot say what something is doing," says Martell. "You have to say it can be any of these things it can be doing—even if the probability is small."

Subatomic particle- protons, neutrons, electrons, and quarks subatomic particle Particles found within an atom Some are located within the nucleus, some are located within the electron cloud

Electron Cloud Model- Modern Model- 20 th century Model Electrons exist in a “cloud” around the nucleus “Electron Cloud”

Bohr Model-Electrons move in orbits around the nucleus- or definite pathways around the nucleus 1913

J. J. Thomson’s plum pudding model- Electrons are scattered in a positively charged area