THE HISTORY OF THE ATOM

Democritus (Greek Philosopher) Timeline: 400BC

400

He was the first person to use the term atom (Atomos: meaning indivisible).
He thought that if you take a piece of matter and divide it and continue dividing it will eventually come to a point where you could not divide it any more.This fundamental or basic unit was what Democritus called an atom He called this as the theory the universe
1. All matter consists of atoms, which are bits of matter to small to be seen
2. Each atom (of a different substance) is different in size, weight and shape

JOHN DALTON. Time line: 1800

1803

He was the first to adapt Democritus theory into the first modern atomic model.
1. All matter consists of tiny particles called atmos.
2. Atoms are indestructible and unchangeable.
3. Elements are characterized by the weight of their atoms.
4. When elements react, it is their atoms that have combined to from new compounds.

J.J.THOMSON. Time line: 1890

1904

He was a physicist who is creadited for discovering the electron. He used his research on cathode ray tube technology in this discovery.
1. An electric charge is passed through the tube. Travels from cathode to anode
2. The charge is invisible, so to see where it traveled a fluorescent screens is placed at back of tube will light up.
3. Thompson showed (as in the diagram above) that the charge would deflect away from the negative coil. He then stated that this charge was thus a negative charge.

THOMSON´S ATOMIC MODEL

1904

Using what he had dicovered, Thomson predected what an atom should look like. These are the key points to Thomson´s Atomic Model:
1. Because of its design, this model was known as the plum pudding model,
2. Each atom is a sphere filled with positively charged "fluid". This resembles the sticky jam part of a pudding.
3. Corpuscles (later called electrons), are the negatively charged particles suspended in this "fluid" resembles the plums in the pudding.

ERNEST RUTHERFORD. Time line: 1910

1911

He was not convinced about the model of the atom proposed by Thomson. He thus set up his now famous GOLD FAIL Experiment
1. He fired alpha particles (positively charged) at a gold foil.
2. He measured the deflection as the particles came out the other side.
3. Most of the particles did not deflect at all. Every now and then, a particle would deflect all the way back.
4. He said that there must be a positive center of the foil. He called this center NUCLEUS.

RUTHERFORD´S ATOMIC MODEL-AKA PLANETARY MODEL

1911

1. Nucleus of the atom is a dense mass of positively charged particles.
2. The electrons orbit the nucleus.
3. A problem raised was: Why are the negatively charged particles not attracted by the positively charged nucleus.
4. Rutherford stated that the atom was like a mini solar system and that the electrons orbited the nucleus in a wide orbit. That is why is known as THE PLANETARY MODEL.

NIELS BOHR.Time line:1910

1913

He was agreed whit the planetary model of the atom but aslo knew that is has few flows, using his knowledge of energy and quantum physics he was able to perfect Rutherford´s model. He was able to answer why the electrons did no collapse into the nucleus.

BOHR´S ATOMIC MODEL (AKA THE RUTHERFORD-BOHR MODEL)

1913

1. Electrons orbit the nucleus in orbits that have a set size and energy.
2. The lower the energy of the electron, the lower the orbit.
3. The means that as electrons fill up the orbitals, they will fill the lower energy level first.
4. If that energy level is fill (or at capacity), a new energy level will begin
5. Radiation is when an electron moves from one level to another

ERWIN ESCHRODINGER. Time line: 1920

1926

He was a revolutionary physicist who use Heisenberg´s uncertainty principle to come up with the atomic model that we still use today.
1. An electron doesn´t travel in a specific orbit
2. We can predict where it will probably be.
3. We cannot say for certain where it is, but where ought to be.
4. The type of probability orbit is dependent on the energy level by Bohr.