Atomic Theory History

Atomic Theory Notes Part 1

Today's Agenda Question

​Historically, how did our understanding of the building blocks of matter evolve?

Open Ended

​Historically, how did our understanding of the building blocks of matter evolve?

Atomic Theory Intro

• Scientists

• Experiments

• Laws and Theories

• The atom

​Overview

Timeline and Scientists

Vocabulary

atoms

The basic building blocks of matter consist of a nucleus containing protons and neutrons,

surrounded by electrons.
nucleus
The positively charged central core of an atom, containing protons and neutrons. (*mass of atom)

Democritus (400 B.C. / Greece)

​Known For:
Atomism
Everything is made of invisible spheres
Experiment: Guessed (no scientific data)

​“Nothing exists except atoms and empty space; everything else is opinion.” – Democritus.

​Aristotle

​Directly argued against atomism. More popular philosopher

Multiple Choice

What was Democritus (c. 400 BCE) known for?

• He was known for the atomism theory.

• He was known for developing the laws of motion.

John Dalton (1808 / England)

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

1. All matter is composed of atoms.

2. Atoms of a given element are identical.

3. Atoms cannot be divided, created, or destroyed.

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

Visual Representation

Multiple Choice

Which of the following options is one of Dalton's Atomic postulates?

• All matter is composed of molecules.
• All matter is made up of indivisible atoms.

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

Multiple Choice

J.J. Thompson discovered the ________ using a cathode ray tube experiment.

• proton
• electron

Ernest Rutherford (1911 / England)

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

Experiment:
Gold Foil Experiment

Visual Representation

Multiple Choice

Rutherford discovered protons had a ________ charge.

• Positive

• Negative

• Neutral

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"

Multiple Choice

Which of theses describes Bohr's atomic principle?

• Electrons occupy fixed orbits around the nucleus.
• Electrons are randomly distributed throughout the nucleus.

Erwin Schrödinger (1926 / Austria)

​Known For: Quantum mechanics

Electrons can only exist in specified energy states.

Experiment:
mathematical equations

Visual Representation
"Electron Cloud model"

Heisenberg’s Uncertainty Principle (1927)

Known For: Quantum Physics
The more precisely the position of a particle is known, the less precisely its momentum can be known, and vice versa

Multiple Choice

Mathematician Heisenberg determined what about electrons?

• Heisenberg determined that electrons can be observed without any limitations.
• Heisenberg determined that the position and momentum of electrons cannot be precisely known at the same time.

James Chadwick (1932 / England)

​Known For: Discovered neutrons

neutral particles in the nucleus of an atom

Experiment:
Mathematical equations (the atom was too light with just protons)

Visual Representation
"Quantum model"

​https://www.youtube.com/watch?v=R8r9kXwgdbA

Multiple Choice

Chadwick another mathematician solved the "missing mass" problem and the neutron, which has a ____________ charge.

• neutral

• positive

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

Law

​​Matter/Mass is neither created nor destroyed

​Conservation of Mass

Theories

​Dalton’s Atomic Theory: Dalton

• All matter is composed of atoms.

• Atoms of a given element are identical.

• Atoms cannot be divided, created, or destroyed.

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

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

Quantum Theory:

1. Atoms are composed of smaller particles.
2. Atoms can vary in mass due to the presence of neutrons.)

Open Ended

Describe a fact you learned in class about the history of the atomic theory.