The History of an Atom

The History of an Atom

Mr. Mendoza

Who even came up with that word?

Democritus(Greek Philospher)

Timeline 400 BC

The first person to use the term "atom"

Greek Word: Atomos=Indivisible

Democritus

thought that if you take a piece of matter and divide it and continue to divide it you will eventually come to a point where you could not divide it any more.

Atom-Fundamental/ basic unit of matter

Theory of the Universe

All matter consists of atoms, which are bits of matter too small to be seen.

There is an empty space between atoms Atoms are completely solid Atoms have no internal structure

Each atom (of a different substance) is different in size, weight and shape. 

Antoine Lavoisier

Timeline: 1780's

Law of Conservation Mass: mass is neither created nor destroyed in chemical reactions

John Dalton

Timeline: 1800s

The first to adapt to Democritus’ theory into the first modern atomic model. 

Dalton's Atomic Model

1. All matter consists of tiny particles called atoms

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 form new compound

Open Ended

Describe the contribution of Democritus to modern atomic theory.

Open Ended

What are the four essential points of Dalton’s atomic theory?

JJ Thomson

Timeline: 1800's

J.J Thomson was a physicist who is credited for discovering the electron. He used his research on cathode ray tube technology in this discovery. 

Thomson's Atomic Model

Thomson's prediction what an atom should look likpe. 

"Plum, Pudding"

Plum Pudding Model

Each atom is a sphere filled with positively charged ‘fluid’. This resembles the sticky jam part of a pudding.

Corpuscles (later called electrons), are the negatively charged particles suspended in this ‘fluid’. This resembles the plums in the pudding.

He did not predict the movement of these electrons

Multiple Choice

What did Thomson discover?

• electron

• proton

• neutron

• electron cloud

Multiple Choice

JJ Thomson's theory was nicknamed _______.

• Billiard Ball Theory

• Solar System Theory

• Electron Cloud

• Plum Pudding

Multiple Choice

Which scientist developed the atomic theory?

• JJ Thomson

• Ernest Rutherford

• John Dalton

• James Chadwick

Ernest Rutherford

Timeline: 1910's

What do you think he thought about Thomson's Model?

Ernest Rutherford

was not convinced about the model of the atom proposed by Thomson.

"Gold Foil Experiment"

Gold Foil Experiment

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 centre of the foil. He called this centre the nucleus.

Rutherford's Atomic Model

1. The nucleus of the atom is a dense mass of positively charged particles.

2. The electrons orbit the nucleus

Planetary Model

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 it is known as the planetary model. 

Niels Bohr

Timeline: 1910's

Niels Bohr agreed with the planetary model of the atom...for the most part.

(quantum physics)He was able to perfect Rutherford’s model.

Why the electrons did not collapse into the nucleus?

Bohr's Atomic Model aka Rutherford-Bohr Model

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. This means that as electrons fill up the orbitals, they will fill the lower energy level first.

Bohr's Atomic Model aka Rutherford-Bohr Model

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.

Bohr's Atomic Model aka Rutherford-Bohr Model

Problem:

Electrons do not travel on a specific orbit or path.

Erwin Schrödinger

Used Heisenberg’s uncertainty principle to come up with the atomic model that we still use today.

Schrödinger's Atomic Model

1. An electron does not travel in an exact orbit

2. We can predict where it will probably be

3. We cannot say for certain where it is, but only where it ought to be.

4. The type of probability orbit is dependent on the energy level described by Bohr

RECAPPING

• The smallest part of an element is called an atom 

• Each atom (of an element) is different in structure from other atoms (of other elements) 

• An atom can be divided in smaller subatomic particles: Protons, Electrons and Neutrons 

• The nucleus is the centre of an atom. It contains protons and neutrons. 

RECAPPING

• Electrons orbit the nucleus  

• Electrons occupy a certain energy level (of a certain size)

• Once the energy level is full, a new level begins

• Within each of these levels are specials types of orbitals. These depend on the energy level 

• Each orbital can contain up to two electrons