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History of the Atom
Transcript of History of the Atom
330 B.C.E: Aristotle
1803 CE: John Dalton
1897: J.J Thompson
Determined the electron has a negative charge:
1. Shot an electrical charge through a Cathode Ray Tube filled with Argon gas and saw a stream or particles (originally William Crookes' experiment)
2. Set up magnets and noted that the particle stream bent toward the positive magnet
Plum Pudding Model
Updated the model of the atom to the "Plum Pudding Model"
Imagine this like a chocolate chip cookie IF:
-chocolate chips are the randomly distributed negative electrons
-cookie batter is a sphere of positive charge (remember, the atom is electrically neutral)
Conducted the Gold Foil Experiment in which he shot large, positive particles (alpha particles) at gold foil
400 B.C.E: Democritus
Matter is made of tiny, indivisible things called "atomos"
Everything is made of four elements: fire, water, air, and earth
The results were not what he expected so he updated the model of the atoms to show that:
-the nucleus is small, dense, and positively charged
-electrons are outside the nucleus
-the atoms is mostly empty space
Found that atoms give off a particular light wavelengths due to the amount of energy they have and updated the model of the atom to the "Planetary Model":
1. Electrons orbit the nucleus like planets in a solar system
2. Each electron orbital has a fixed energy level (1-7)
3. When electrons gain or lose a specific amount (quantum) of energy, they can move from one level to another.
1932: Erwin Schrodinger
Electrons are moving at the speed of light so you cannot determine their exact location, only a probability of location. This is represented by a cloud and led to the "Quantum Mechanical Model":
-each energy sublevel corresponds to one or more orbitals of different shapes that describe where an electron can be found