ATOMIC THEORY TIMELINE

Timeline and Scientists

The History of an Atom

Mr. Mendoza

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

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

Open Ended

Describe the contribution of Democritus to modern 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

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

• 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

Atomic Model Through the Years

Indivisible

Electron

Nucleus

Orbit

Electron

Cloud

Greek

X

Dalton

X

Thomson

X

Rutherford

X

X

Bohr

X

X

X

Wave

X

X

X

Multiple Choice

John Dalton stated:

• Atoms are tiny, invisible particles.

• Atoms of one element are all the same.

• Atoms of different elements are different.

• Compounds form by combining atoms.

• All of the statements listed.

Multiple Choice

All matter is made of what?

• energy
• electrons
• atoms
• compounds

Multiple Choice

How did Rutherford discover the proton?

• Cathode Ray Tube
• Gold Foil Experiment
• Planetary Model
• Plum Pudding Model

Multiple Choice

J.J. Thomson provided evidence that an atom...

• is the smallest particle of matter
• contains negatively and positively charged particles
• has an overall negative charge
• has an overall positive charge

Multiple Choice

What scientist is best known for his "Plum Pudding" model of the atom?

• J.J. Thomson
• Ernest Rutherford
• John Dalton
• Democritus

Multiple Choice

Which subatomic particle has a neutral charge and is found inside the nucleus?

• Electrons

• Protons

• Neutrons

• Nucleus

Multiple Choice

True or False: Electrons are found in the nucleus.

• True

• False

Multiple Choice

What is the smallest unit of matter that still has the properties of an element?

• Atom

• Proton

• Neutron

• Electron

Multiple Choice

Which scientist developed this model?

• Dalton

• Thomson

• Rutherford

• Bohr

Multiple Choice

Which scientist developed this model?

• Dalton

• Thomson

• Rutherford

• Bohr

Democritus (400 B.C. / Greece)

​Known For: naming the atom
Atomos: means uncuttable in Greek
Experiment: Guessed (no scientific data)

​

​Visual Representation

Aristotle (384 B.C. to 322 B.C.)

Thought that all materials on Earth were not made of atoms, but of the four elements, Earth, Fire, Water, and Air.

His theory held true for the next 2000 years.

Open Ended

Why do you think Aristotle's theory of the atom was more accepted than Democritus' theory?

John Dalton (1808 / England)

​Known For: Atoms were indivisible (cannot be divided)

The Laws
1. Law of Conservation
2. Law of Definite Proportions
3. Law of Multiple Proportions

Visual Representation

Summarize in your own words

J.J. Thomson (1897 / England)

​Known For: electrons were smaller particles of an atom and were negatively charged.

Experiment:
Cathode Ray Tube Experiment

Visual Representation

Ernest Rutherford (1911 / England)

​Known For: Protons (positive charged) and atoms were mostly empty space

Experiment:
Gold Foil Experiment

Visual Representation

Vocabulary

Alpha particles (a)

are composite particles consisting of two protons and two neutrons tightly bound together

Niels Bohr (1913 / England)

​Known For: Energy levels of electrons
Electrons can jump across energy levels

Experiment:
Emissions Spectrum (color of light)

Visual Representation
"Planetary model"

Erwin Schrödinger (1926 / Austria)

A.K.A.: Modern Model of the Atom

​Known For: Quantum mechanics

electrons can only exist in specified energy states

Experiment:
mathematical equations

Visual Representation
"Electron Cloud model"

James Chadwick (1932 / England)

​Known For: Discovered neutrons

neutral particles in the nucleus of an atom

Experiment:
mathematical equations (atom was too heavy with just protons)

Visual Representation
"Quantum model"

Summary of what is known about the current model of the atom:

​Subatomic Particles	​Symbol	​Relative charge	​Relative mass (amu)	​Actual mass
​electrons	​e	-1	​1/1840	​9.11 X 10-28
​protons	​p	​+1	​1	​1.67 X 10-24
​neutrons	o	0 ​(no charge) (neutral)	​1	​1.67 X 10-24

Theories

​Dalton’s Atomic Theory: Dalton

1. All matter is composed of atoms.

2. Atoms of a given element are identical

   • Today: Not true - there are isotopes

3. Atoms cannot be divided, created, or destroyed

   • Technically, no, but there are smaller parts (p, n, and e)

4. Atoms of different elements combine in simple whole number ratios to form chemical compounds.

5. In chemical reactions, atoms are separated, rearranged, or combined.

Quantum Theory
1. Atoms are made of smaller particles

2. Atoms of the same element (isotopes) can vary in mass (neutrons)