Atomic Theory
Part 1
History and Scientists
Chemistry
Learning Objectives
• TLW research and describe the historical
development of atomic theory (TEKS 6)
• TLW be introduced to the scientists behind
the atomic theory (TEKS 3.F. & 6.A.)
• TLW begin to describe the relationship
among electrons, protons, neutrons, atomic
number, mass number, and isotopes (TEKS
6A, 6B, 11A)
Anticipatory Activity
What’s in the Box? Lab – to be done prior to
beginning lecture from this PowerPoint
Agenda
• I. Atoms – Building Blocks of Matter &
Subatomic Particles
• II. Mass of Atoms
• III. Meet the Scientists and Learn About
Their Discoveries
• IV. Modern Day Atomic Theory
I. Atoms
A. Building blocks of Matter
1. Everything is made up of atoms
2. Atom is Greek for indivisible
3. There are three major parts to
the atom called subatomic
particles
B. Subatomic Particles
ATOM
ATOM
Ions – lose/gain
electrons
Cation – positive
Anion -- negative
NUCLEUS
NUCLEUS
ELECTRONS
ELECTRONS
PROTONS
PROTONS
NEUTRONS
NEUTRONS
NEGATIVECHARGE
CHARGE
NEGATIVE
POSITIVE
POSITIVE
CHARGE
CHARGE
NEUTRAL
NEUTRAL
CHARGE
CHARGE
Isotope – same number
of protons, different
number of neutrons
QUARKS
Atomic Number
equals the # of...
equal in a
neutral atom
Most of the atom’s mass.
II. The Mass of Atom
A. Protons
1. are positively charge
2. have a mass of 1.67 X 10-27 kg
3. Found in the nucleus
B. Neutrons
1. Neutral
2. have a mass of 1.67 X 10-27 kg
3. Found in the nucleus
C. Electrons
1. are negatively charged
2. Have a mass of 9.11 X 10-31 kg
3. Found orbiting outside the nucleus
To Put Nucleus Size in Perspective
If an atom were the size of this stadium,
then its nucleus would be about the size of
a marble
Something “Quarky” About Atoms
• Quarks are fundamental matter particles that
make up protons and neutrons
• 6 types – up, down, charm, strange, top, bottom
• Only 2 (up and down) exist in protons and
neutrons, others are unstable and randomly
occur
• We have yet to determine their mass
• Quarks and electrons are considered to be the
smallest units of matter in the universe
III. The Scientists and their
Discoveries
Democritus
ATOM
Smallest
particle
Democritus (Greek philosopher)
1. Date = 400 B.C
2. Discovery = Theorized the
smallest unit of an element
3. Importance = gave the term
and definition of atom
4. Atom is Greek for “unable to divide”
5. Believed movement of atoms caused
changes in matter he observed, but
couldn’t prove it with evidence people
would accept
John Dalton
Atomic Theory
Molecules
made of
atoms
John Dalton
1. Date = 1803
2. Discovery =
a. Every element is made of
atoms
b. atoms of same element
exactly the same
c. Atoms of different elements
join together to form molecules
Importance = proposed the ATOMIC THEORY
Atomic Theory (in beginning) =
1. everything is made up of atoms
2. atoms make up molecules
3. atoms of the same element are the same
4. Atoms cannot be divided
5. in chemical reactions, atoms are combined,
separated, rearranged..
…. BUT NEVER destroyed
6. aka Law of Conservation of Mass
Dimitri Mendeleev
1. Date = ca. 1870
2. Discovery =
a. Order of elements is based on the
periodic law
b. Periodic Law states properties of
elements will occur in a regular pattern
3. Importance =
First periodic table of elements…
….arranged by mass
Mendeleev’s Periodic Table
Eugen Goldstein
1. Date = 1886
2. Discovery =
a. discovered protons using cathode
ray tube. Rays were observed traveling
in the direction opposite of the
cathode rays.
b. protons are positive
3. Importance =
atoms have both negative and
positive particles
4. How?
a. Using a cathode ray
b. relationship between
electricity and matter
c. electric current was passed through
various gases at low pressure in a glass
tube = cathode
d. In Goldstein’s Experiment: Rays were
observed traveling in the direction
opposite of the cathode rays.
e. Later we’ll learn that In Thomson’s Experiment:
Cathode Rays were attracted to positive
electrical charges.
Discovery of the Protron
In 1886, Eugen Goldstein used a cathode ray tube to
discover the presence of a positively charged
particle called a proton.
Cathode ray tubes pass electricity through a gas
that is contained at a very low pressure.
William Crookes
1. Date = 1887
2. Discovery =
a. discovered metals contain
negatively charged particles
3. Importance =
early indication of the electron
J.J. Thomson
“Plum Pudding”
model
Electrons are
negative
J.J. Thomson
1. Date = 1898
2. Discovery =
a. discovered electrons
b. electrons are negative
3. Importance =
atoms have both negative and
positive particles
Discovery of the Electron
In 1897, J.J. Thomson used a cathode ray tube to
discover the presence of a negatively charged
particle called an electron.
Cathode ray tubes pass electricity through a gas
that is contained at a very low pressure.
Max Planck
1. Date = 1899
2. Discovery =
a. hot objects don’t emit energy
continuously, like in a wave
b. instead, energy is emitted in
small, specific amounts called quanta
3. Importance =
original idea of quantum theory
Ernest
Rutherford
Discovered
nucleus
Gold Foil
Experiment
Electrons
outside
nucleus
Ernest Rutherford
1. Date = 1911
2. Discovery =
a. discovered nucleus
b. did a “gold foil” experiment
c. atoms mostly made of space
3. Importance =
a. nucleus is very tiny, and
positively charged
b. electrons outside of nucleus
Rutherford’s Gold Foil Experiment
 Alpha particles are helium nuclei
 Particles were fired at a thin sheet of gold foil
 Particle hits on the detecting screen (film) are
recorded
Try it Yourself!
In the following pictures, there is a target hidden by a
cloud. To figure out the shape of the target, we shot
some beams into the cloud and recorded where the
beams came out. Can you figure out the shape of the
target?
The Answers
Target #1
Target #2
Rutherford’s Experiment
• As a follow up to our Introductory Activity of What’s in the
Box?…
• We will now conduct a simple experiment to determine
the size and shape of an object by indirect means…. as
did Rutherford when he developed Atomic Theory
– See pages 45 & 46 in Chemistry Lab Manual
(Prentiss Hall)
– See IPC Manual pages 122 & 123
Marie Skodowska Curie
1. Date = 1911
2. Discovery =
a. Radioactivity of isotopes
3. Importance =
paved way for use of radioactive
isotopes in medical field and
other applications
Henry Moseley
1. Date = 1913
2. Discovery = used x-ray
technology to measure the
number of protons in an atom
3. Importance = led to better
arrangement of Periodic Table by
atomic number
(more on the PT later….)
Robert Millakan
1. Date = 1916
2. Discovery =
a. measured the quantity of charge
on the electron
b. determined ratio of charge to
mass of an electron
3. Importance = determined mass
of an electron
Discovery Education
Early Nuclear Theory
Niels Bohr
Electrons in energy
levels (orbits)
Niels Bohr
1. Date = 1913
2. Discovery =
a. Electrons are in energy levels
b. s, p, d, f orbitals
c. 1st = 2 electrons;
2nd = 8 electrons;
3rd = 18 electrons
4th = 32 electrons
Energy Levels (more)
• Fixed energy levels are analogous to rungs on a
ladder
• A person cannot stand between them, they climb
from one to another to reach a greater height
• Similarly, an electron cannot exist between
energy levels
• To jump from one energy level to another the
electron must gain or lose energy
Quantums of Energy
• Have you heard of the term “quantum
leap”?
• A quantum of energy is the amount of
energy required to move an electron
from its present energy level to the
next higher one.
• The higher the electron is on energy
ladder, the farther it is from nucleus
3. Importance =
electrons orbit around nucleus in a
certain pathway like planets around
the sun.
This is the
Bohr Model
Bohr’s Model and What It Led To
• Discovery Streaming VIDEO
Wolfgang Pauli
1. Date = 1925
2. Discovery = only one electron can
occupy a given quantum state
3. Importance = determined how
electrons pair up and the direction of
their movement
Erwin Schrödinger
•Atoms have no charge
•Same number of protons and
electrons
Quantum
Mechanical Model
Erwin Schrödinger
1. Date = 1926
2. Discovery = electrons are
impossible to find (like moving
fan blades)
3. Importance =
a. Developed Quantum Mechanical
Model
b. Atoms are neutral
c. Atoms must have the same
number of protons and electrons
Quantum Mechanical Model
• Mathematically based
• Does not define an exact path for
electrons as did Bohr’s Model (orbitals)
• Estimates the probability of finding an
electron in a certain position
• Sheldon from The Big Bang Theory sitcom explains
Schrodinger’s Cat Model (YouTube)
• Another YouTube video of Schrodinger’s Cat
Werner Heisenberg
1. Date = 1927
2. Discovery =
can’t simultaneously
determine position and
momentum of a particle
3. Importance = predicted better known
the position, less known of
momentum
YouTube video on Heisenberg’s Uncertainty Principle
Another YouTube video on H’s Uncertainty Principle
James Chadwick
1. Date = 1932
2. Discovery = demonstrated
existence of neutron
3. Importance = this accounted
for the additional mass in the
nucleus of an atom
IV. Modern Day Atomic Theory
1. All matter is composed of atoms
2. Atoms of different elements have
different properties and masses
3. Atoms can combine in chemical reactions
(law of conservation of mass)
4. Atoms can be divided
5. Elements of the same atom can have
different masses
– Called isotopes – more later
Projects
• Atomic Timeline • For more on other contributors and
exciting moments in atomic theory history
click on this link
• FactBook Page for Scientist - link
IV. Section Questions
1. Which “scientist” gave us the word atom?
2. Which scientist developed the atomic
theory?
3. Every element is made of atoms, atoms
of the same element are exactly the
same, different atoms make up
molecules. These statements make up
the what?
4. Which scientist discovered the
electrons?
5. Which scientist discovered the
nucleus?
6. Which scientist discovered that
electrons were in energy levels?
7. Which scientist said atoms were neutral
because they had equal number of
protons and electrons?
8. What is the mass of protons?
9. What is the mass of neutrons?
10. What is the mass of electrons?
11. Which part of the atom has the least
amount of mass?
Review Key Points
• Atoms are building blocks for all matter
– Name the subatomic particles
• Name key scientists and their work in
atomic theory
• List the 5 points of modern atomic theory
Independent Practice
• Atomic Theory Timeline Project link
or
• Atomic Theorists FACTBook page link
• Word Search – write the word with its
definition on the back
• Crossword Puzzle