Development of the
Atomic Model
Ethil L. Carbo
Labogon national High School

Development of the
Atomic Model

Objectives:
describe different models of the atom;
draw a diagrammatic model of an
atom to explain their understanding
about the different atomic models;
explain how the atomic models help
in understanding the concept of an
atom.

What is matter to you?
What is matter made of?

Get a strip of paper. Cut the paper in half. Take one of
the halves and cut it into half. Continue this process
and until you no longer able to cut in half, keep
count of how many times the paper has been cut.
How many times did you able to
cut the strip of paper?

Cut 1 14.0 cm 5.5" Child's hand, pockets
Cut 2 7.0 cm 2.75" Fingers, ears, toes
Cut 3 3.5 cm 1.38" Watch, mushroom, eye
Cut 4 1.75 cm 0.69" Keyboard keys, rings, insects
Cut 6 0.44 cm 0.17" Black pepper seeds
Cut 8 1 mm 0.04" Thread Congratulations if you’re still in!
Cut 10 0.25 mm 0.01" Still cutting? Most have quit by now
Cut 12 0.06 mm 0.002" Microscopic range, human hair
Cut 14 0.015 mm 0.006" Width of paper, microchip components
Cut 18 1 micron 0.0004" Water purification openings, bacteria
Cut 19 0.5 micron 0.000018" Visible light waves
Cut 24 0.015 micron 0.0000006" Electron microscope range, membranes
Cut 31 0.0001 micron 0.0000000045" The size of an Atom!

Have you ever wondered how the
atom looks like?

Activity
1.Divide the class into 5 groups according to their
name tag color.
2.Draw your own diagrammatic model of an atom in a
long bond paper.
3. Rank the models as best, better, and good.
4. Choose a representative from your group to
share your ideas on the way you rank the models?

Guide Questions:
1. What criteria did you use to make your
ranking?
2. Why did you choose the way you did?
3.Why do you think the best model is better
than the others?
4. Which models did you like least? Why?

Who are these men?
Unscramble the letter to reveal the name of these
men.

Who are these men?
DMEOCIRTUS

Who are these men?
DEMOCRITUS

Who are these men?
JHNO ALDTON

Who are these men?
JOHN DALTON

Who are these men?
OHJN JSEPHO TOHMSNO

Who are these men?
JOHN JOSEPH THOMSON

Who are these men?
NEREST RUTEHRFDOR

Who are these men?
ERNEST RUTHERFORD

Who are these men?
SLINE ORBH

Who are these men?
NEILS BOHR

NEIL BORH
ERNEST RUTHERFORD DEMOCRITUS J.J. THOMSON
JOHN DALTON
In this lesson, we’ll learn about the men whose
quests for knowledge about the fundamental nature of
the atom.

Democritus 470-380 B.C
was a Greek philosopher (470-380 B.C.)
who is the father of modern atomic
thought.
He proposed that matter could NOT be
divided into smaller pieces forever,
eventually the smallest possible piece
would be obtained.
This piece would be indivisible.

Democritus 460-380 B.C
He believed that matter was made of
small, hard, particles, that he called
“atomos” meaning “uncuttable.”
To Democritus, atoms were small, hard
particles that were all made of the same
material but were different shapes and
sizes.
Atoms were infinite in number, always
moving and capable of joining together.

This theory was ignored and
forgotten for more than 2000
years!

Aristotle 384-322 B.C
did not believe in the atomic theory . He
doesn’t believe empty space could exist,
and he taught so otherwise.
He thought that all materials on Earth
were not made of atoms, but of the four
elements, Earth, Fire, Water, and Air.
He believed all substances were made
of small amounts of these four elements
of matter.

Aristotle 384-322 B.C
Most people followed Aristotle’s idea,
causing Democritus’ idea- which was
that all substances on Earth were made
of small particles called atoms- to be
overlooked for about 2,000 years!
Aristotle's view was finally proven
incorrect, and his teachings are not
present in the modern view of the atom.

John Dalton – English (1766 – 1844)
In the early 1800s, the English
Chemist John Dalton performed a
number of experiments that
eventually led to the acceptance of the
idea of atoms. Marks the beginning of
the development of modern atomic
theory.
Dalton and Democritus are similar
Dalton’s research is known as Dalton’s
Atomic Theory which was proposed in

Dalton’s Early Atomic Model
Suggested that all matter was made
up of TINY SPHERES that were able
to bounce around with perfect
elasticity. • Called them ATOMS
He envisioned atoms as solid, hard
spheres, like billiard(pool) balls, so he
used wooden balls to model them.
“Billiard Ball” model

Dalton’s Theory
1. All matter is comprised of tiny, definite particle called
atom. Atoms are indivisible and indestructible particles.
2. Atoms of the same element are exactly alike. The atom of
one element are different from the atoms of other elements.

Dalton’s Theory
3. Atoms cannot be created or destroyed during a chemical
reaction and the atoms of one element cannot change into
the atom of another element.
4. Compounds are formed by the joining of atoms of two or
more elements. Compounds and reactants contain the same
total number of particles.

Dalton’s Theory
This theory became one of the foundations
of modern chemistry.

But Wait….
Experimental studies of the atom
soon showed that it (the atom) was
not indivisible… it has smaller parts!

Thomson’s Plum Pudding Model
In 1897, the English scientist J.J.
Thomson provided the first hint that
an atom is made of even smaller
particles.
Just over 100 years ago, J. J. Thomson
discovered that electrons are
relatively low mass, negatively
charged particles present in atoms.

Thomson’s Plum Pudding Model
He discovered it by doing experiment
using cathode ray tube. He was the
first scientist to show that atom was
made of even smaller thing.
He proposed a model in which the
atom consists of a uniform distribution
of positive charge, in which electrons
are embedded (like raisins in plum
pudding). “The Plum Pudding” Model

Thomson’s Experiment
Used the Cathode ray tube to discover electrons

Thomson’s Experiment
Voltage source
+
-
Vacuum tube
Metal Disks

Thomson’s Experiment
Voltage source
+
-

Thomson’s Experiment
Voltage source
+
-

Passing an electric current makes a beam
appear to move from the negative to the
positive end
Thomson’s Experiment
Voltage source
+
-

 Passing an electric current makes a beam
appear to move from the negative to the
positive end
Thomson’s Experiment
Voltage source
+
-

Passing an electric current makes a beam
appear to move from the negative to the
positive end
Thomson’s Experiment
Voltage source
+
-

Passing an electric current makes a beam
appear to move from the negative to the
positive end
Thomson’s Experiment
Voltage source
+
-

Voltage source
Thomson’s Experiment
By adding an electric field

Voltage source
Thomson’s Experiment
By adding an electric field
+
-

Voltage source
Thomson’s Experiment
+
-
By adding an electric field

Voltage source
Thomson’s Experiment
+
-
By adding an electric field

Voltage source
Thomson’s Experiment
+
-
By adding an electric field

Voltage source
Thomson’s Experiment
Adding an electric field cause the beam to move
toward the positive plate.
Thomson concluded the beam was made of negative
moving pieces.
+
-
-

Thomson’s “Plum Pudding” Atom Model

Using a cathode ray tube, he discovered canal rays
which are beams of positively charged particles.
He is credited with the discovery of protons in an
atom.
Canal Rays discovery
Eugen Goldstein 1850-1930

Ernest Rutherford- Nuclear Model
He continued his teacher, J.J.
Thomson’s research. He used alpha
ray that shot to atom using gold foil.
Rutherford’s experiment showed that
atoms have positive particle in the
and are mostly an empty space

Ernest Rutherford- Nuclear Model
He hypothesis of atom model is “ atom
consist of nucleus that has positive
charge and surrounding with moving
electrons.
He discovered the nucleus of a gold atom
with his “gold foil” experiment
- dense, positive charge in the
center of the atom

Using J.J Thomson’s Plum Pudding atomic
model, Rutherford predicted the alpha particles
would pass straight though the gold foil. That’s
not what happened.
Rutherford
Experiment

most alpha particles go straight
through the gold foil
A few alpha particles are sharply
deflected by very small amounts.
A very few get deflected greatly.
Even fewer get bounced off the foil
and back to the left.
Gold Foil Experiment Results

Rutherford’s Conclusion
• The atom is mostly empty
space.
• There is a small, dense center
with a positive charge.
• The nucleus is approximately
100,000 times smaller than the
atom.
• Proposed the Nuclear model

Neils Bohr’s Model
While the Rutherford model focused
on describing the nucleus, Niels Bohr
turned his attention to describing the
electron.
improved Rutherford’s idea by adding
that the electrons were in ORBITS. •
Proposed that electrons surround the
nucleus in specific “ENERGY
LEVELS” or “SHELLS. ” • Each orbit
only able to contain a SET NUMBER
of electrons.

Neils Bohr’s Model
He used Hydrogen atom for his experiment and
explain about spectrum of it.
proposed the planetary model
Bohr’s Model

•An atom consists of positively charge nucleus
and the electrons revolve around it in special
orbits called discrete orbits or energy levels
•The energy of these discrete orbits remained
fixed.
•These energy levels are represented by 1,2,3,4 or
K, L, M, N starting from the center
Bohr’s Model of atom suggested that:

James Chadwick
In 1932, Chadwick observed that beryllium, when
exposed to bombardment by alpha particles, released
an unknown radiation that in turn ejected protons
from the nuclei of various substances.
Chadwick interpreted this radiation as being
composed of particles of mass approximately equal to
that of
the proton.
These newly discovered particles
Chadwick’s
Experiment

James Chadwick’s Experiment

Electron Cloud Model
Proponents: Schrodinger, Heisenberg, Einstein and
many other scientists
Thought that the problem with Bohr’s model was
restricting the electrons to specific orbits.
Schrondinger wondered if electrons might behave
like light , which scientist s already knew had
properties of both particles and a waves. He
speculated that electrons might also travel like a
wave.

Electron Cloud Model
According to today’s atomic theory, electrons do not
orbit the nucleus in neat planet-like orbits but move
at high speeds in an electron cloud around the
nucleus.
In the electron cloud, electrons whirl or moved rapidly
around the nucleus billions of times in one second.

Electron Cloud Model
The electron cloud model says that we cannot know
exactly where an electron is at any given time, but
the electrons are more likely to be in specific areas.
You can’t specify the exact location of an electrons.
However, Schrodinger showed that you can at least
determine where an electron is mostly likely to be.

Electron Cloud Model
They are not moving around in random patterns; an
electron’s location depends upon how much energy the
electron has.

Application
Redraw a diagrammatic model of your own model of
an atom. Answer the following questions below and
choose another representative to share views and
understanding about the atom to the class.

Guide Questions
1.What does your new drawing show? What does it not
show?
2.What features of your atom can you show now that you
didn’t show in the first drawing (done before the
activity)?
3. What have you learned about atoms that you didn’t know
before?
4. Why is there more than one correct way of modelling an
atom?
5. What sort of information do you think contributed to the
development of new models of atoms?

Who proposed first that matter is
composed of tiny, indivisible
particles?
Democritus
Let’s Check Your Understanding

Who was the scientist the first to
adapt Democritus’ theory and
proposed the first modern Atomic
Model?
John Dalton

What is Dalton’s atomic model
looks like?
Billiard Ball

Who proposed the plum pudding
model of the atom?
J.J. Thomson

Rutherford ‘s model of the atom
concentrated on the nucleus.
Where did Bohr’s model focused
on?
Electrons

Assignment
Create an Atomic Model Phase book Page- Choose one scientist who contributed
the atomic model for you to research. Include the following information:
a. Profile Name: (place your scientist’s name)
b. Profile Picture: (draw your scientist’s atom)
c. Job: (What did the scientist study?)
d. Years Active: (What years did the scientist work on the atom?)
e. Claim to Fame: (Atomic Theory Discovery/Contribution of this scientist)
f. Memories/Analogy: (clue that will help you remember this scientist’s
model of the atom)