LESSON 4:
CONTENT
CONTENT
STANDARD
LEARNING
COMPETENCIES
How the idea of the atom, along with the idea of the elements evolved
At the end of the lesson, you will have to describe:
1. how the concept of the atom evolved from Ancient Greekto
the present; and
2. how the concept of the element evolved from AncientGreek
to the present
At the end of the lesson, you will have to:
1. point out the main ideas in the discovery of the structure of
the atom and its subatomic particles (S11/12PS-IIIb-8)
2. cite the contributions of J.J. Thomson, Ernest Rutherford,
Henry Moseley, and Niels Bohr to the understanding of the
structure of the atom (S11/12PS-IIIb-9)
3. describe the nuclear model of the atom and thelocation of
its major components (protons, neutrons, and electrons)
(S11/12PS-IIIb-10)
1
A T O M
T B A I L O A
P C R E G M C
What Does
an A t o m
REALLYLook
Like?
RECALL
KEY TERMS
10) Nucleus –
11) Protons –
12) Niels Bohr –
13) Quantum Model –
5) Joseph John Thomson – 14) James Chadwick –
6) Electrons –
15) Neutrons –
1)
2)
3)
4)
Atom –
Billiard ball –
Robert Brown –
John Dalton–
7) Plum-pudding model –
8) Ernest Rutherford –
9) Radioactivity –
ATOM
 The smallest unit of matter as recognized
by chemical properties of molecules.
 composed of protons, neutrons and
electrons.
 very small; typical sizes are around 100
picometers (a ten-billionth of a meter, in the
short scale)
SEATWORK#3
Sub-atomic
Particle of an Atom
Electron
Proton
Neutron
is discovered by
through the…
(what kind of experiment)
J. J. Thomson
cathode ray tube
experiment
Ernest
Rutherfor
d
James
Chadwick
gold foil
experimen
goldt foil
experimen
z
z
ATTRIBUTE OF THE ATOMIC
MODEL
 Conceptualized following
cathode ray experiments
 Has a nucleus
 Has energy levels or quanta
 Conceptualized following αparticle experiments
 Explains why electrons
don’t fall into the nucleus
 Has idea of orbitals
 First model to use idea of
subatomic particles
ATOMIC MODEL
DALTON
THOMSON
RUHTERF
ORD
BOHR
QUANTUM
nucleus
is the small, dense region
consisting of protons and
neutrons at the center of an
atom, discovered in 1911 by Ernest
Rutherford based on the 1909 Geiger–
Marsden gold foil experiment.
radioactivity
 The spontaneous decay of
atomic nuclei.
 During radioactivity, alpha
particles, beta-rays and gamma
rays are emitted.
DEMOCRITUS
460 – 370 B.C.
■ There are various basic elements
from which all matter is made
■ Everything is composed of small
atoms moving in a void
■ Some atoms are round, pointy, oily,
have hooks, etc. to account for their
properties
■ Ideas rejected by leading
philosophers because
void = no existence
DEMOCRITUS
sometimes known as the
BILLIARD BALL
concept of the atom,
wherein the atom is an
incredibly small but
smooth and whole object.
ROBERT BROWN
 He is known for his idea of
the random movement of
microscopic particles or
"Brownian motion."
JohnJODaHltoNn DALTON
1766-1844
IDEA OF AN ATOM
■Introduced his ideas in
1803 that each
element is composed
of extremely small
particles called atoms
Proponent: John Dalton
This model suggested
that atoms:
• are the smallest
particle of an element
• of different elements
have different masses
• are solid,
indestructible units.
J. J. THOMSON
IDEA OF AN ATOM
 Conceptualized
following cathode
ray experiments
 First model to use
idea of subatomic
particles
J. J. THOMSON
IDEA OF AN ATOM
Later in 1897, Joseph John Thomson published the
idea that electricity was in particles that were
part of the atom. Experimenting with cathode rays, he
established the mass and charge properties of
these particles. These particles were named electrons.
In 1904, he came up with the plum-pudding model, which
was an idea of what the atom looked like based on his
experiments.
He would later conclude that the electron was not the only
source of mass in the atom. This implied
that the atom was composed of other particles.
J. J. THOMSON
IDEA OF AN ATOM
Thomson
“Plum Pudding” Model
Actual
Plum Pudding
J. J. THOMSON
Thomson’s plum-pudding model,
a sphere with a
uniformly
distributed positive
charge and enough
embedded electrons
to neutralize the
positive charge. A plum
pudding is a sort of cake with raisins embedded
in it.
IDEA OF AN ATOM
J. J. THOMSON
IDEA OF AN ATOM
Cathode Ray Tube Experiment
ERNEST RUTHERFORD
Has a nucleus
Conceptualized
following α-particle
experiments
IDEA OF AN ATOM
ERNEST RUTHERFORD
IDEA OF AN ATOM
Ernest Rutherford, a student of Thomson’s, who was among
many who studied radioactivity. He concluded that
radioactivity occurred due to changes on a subatomic level,
or changes within the atom itself. In 1902, he worked in
Thomson’s laboratory where he distinguished two kinds of
radiation based on their penetrating power: α (alpha) and β
(beta). He studied these types of radiation and noticed, from
his experiments, that alpha particles would sometimes
bounce off at a high angle when made to penetrate a very
thin gold foil.
ERNEST RUTHERFORD
IDEA OF AN ATOM
In 1911, Rutherford theorized that the model proposed by Thomson did
not explain the deflection of alpha particles. Therefore, he devised his
own model with a positive nucleus at the center and electrons revolving
like planets at a distance around it. The incredibly dense nucleus
explained the occasional deflection experienced by the alpha particles,
while the amounts of empty space in between explained why most
particles were able to pass through.
Rutherford later concluded that the nucleus was composed of positive
particles known as protons, which were then thought to be hydrogen
nuclei found in other atoms. He suggested the possibility of finding a
composite particle (proton + electron) with a negligible electric field
that composed the nucleus.
Diagram of the
Rutherford atomic
model. Physicist Ernest
Rutherford envisioned
the atom as like a
miniature solar
system, with
electrons orbiting
around a massive
nucleus, and as mostly
empty space, with the
nucleus occupying only
a very small part of the
atom.
ERNEST RUTHERFORD
IDEA OF AN ATOM
Gold Foil Experiment
NIELS BOHR
IDEA OF AN ATOM
Has a nucleus
Has energy levels or
quanta
Explains why
electrons don’t fall
into the nucleus
NIELS BOHR
proposed that
the electrons
“jumped”
between energy
levels
IDEA OF AN ATOM
NIELS BOHR
IDEA OF AN ATOM
Niels Bohr, another scientist in Rutherford’s laboratory. He
tackled one of the big issues with the Rutherford model in 1913. The
system proposed by Rutherford was unstable because, under
classical physics, the spinning electrons would tend to be attracted
to the positive nucleus and lose energy until they collapse into the
center. Bohr proposed that the electrons existed only at fixed
distances from the nucleus at set “energy levels,” or quanta. Quanta
was first conceptualized mathematically by Max Planck by absorbing
or releasing discrete amounts of energy.
However, the Bohr model of the atom was still unable to explain why atoms
bonded in certain ways to form compounds. For example, carbon
formed compounds of CH4 while oxygen formed H2O.
NIELS BOHR
IDEA OF AN ATOM
In the Bohr model of the atom,
electrons travel in defined circular
orbits around the nucleus.
The orbits are labeled by an integer,
the quantum number n.
Electrons can jump from one orbit to
another by emitting or absorbing
energy.
Schrödinger
Werner Heisenberg
Ernst
IDEA OF
AN ATOM
QUANTUM MODEL
 Has a nucleus
 Has energy levels or quanta
 Explains why electrons
don’t fall into the nucleus
 Has idea of orbitals
Schrödinger
Werner Heisenberg
Ernst
IDEA OF
AN ATOM
• In quantum mechanics, this branch
augmented the Bohr model with new
explanations of how matter behaved at a very
tiny level that turned it into the quantum model
of the atom used today.
• The model is based on mathematical
equations by several scientists, including
Werner Heisenberg and Ernest Schrödinger
Quantum model
 This model uses complex
shapes of orbitals (sometimes
called electron clouds), volumes
of space in which there is likely
to be an electron.
Quantum model
JAMES CHADWICK
James Chadwick was a student of
Rutherford’s who built on this
possibility in 1926. He worked on
radiation emitted by beryllium that
took the form of particles heavy
enough to displace protons.
JAMES CHADWICK
These particles were as heavy as
protons, but they needed to have a
neutral charge that would allow
them to smash into the nucleus
without being repelled by electrons
or protons. He confirmed their
existence by measuring their mass
and called them NEUTRONS.
JAMES CHADWICK
The neutron was able to explain the mass unaccounted for by a
system of protons and electrons only.
It also allowed for more far-reaching advancements in nuclear
physics and chemistry.
It gave an understanding of isotopes and radioactive decay, and
provided the tools to synthesize new elements and radioactive
materials. These advancements, for better or for worse,
changed the landscape of science because they gave us the
ability to derive large amounts of energy from splitting the atom
(nuclear fission).
JAMES CHADWICK
Gold Foil Experiment
What Does
an A t o m
REALLYLook
Like?
Here are a few atoms using Scanning Transmission Electron
Microscopy Single Atom Spectroscopy
Here is how the hydrogen orbits look like using a photoionization quantum microscope Hydrogen
Atoms under Magnification: Direct Observation of the Nodal Structure of Stark States
Ateam of researchers from China’s National Center for Nanoscience & Technology and Renmin
University have utilized atomic force microscopy (AFM) to produce a high-resolution image of atoms
reaching out to make a link with each other.
Research paper: DOI: 10.1126/science.1242603 – “Real-Space Identification of Intermolecular Bonding with Atomic
Force Microscopy” (paywall)
SEATWORK#3
Sub-atomic
Particle of an Atom
Electron
Proton
Neutron
is discovered by
through the…
(what kind of experiment)
J. J. Thomson
cathode ray tube
experiment
Ernest
Rutherfor
d
James
Chadwick
gold foil
experimen
goldt foil
experimen
z
z
ATTRIBUTE OF THE ATOMIC
MODEL
 Conceptualized following
cathode ray experiments
 Has a nucleus
 Has energy levels or quanta
 Conceptualized following αparticle experiments
 Explains why electrons
don’t fall into the nucleus
 Has idea of orbitals
 First model to use idea of
subatomic particles
ATOMIC MODEL
DALTON
THOMSON
RUTHER
FORD
BOHR
QUANTUM
GRADE 12-MAGSAYSAY
1. DEMOCRATUS:ebdane-sotomayor
2. JOHN DALTON:capunan-agimlod
3. JJ THOMPSON:gian-rodz
4. ERNEST RUTHERFORD:ba-at - marundan
5. NEILS BOHR:pondolanan - lintapan
6. SCHROEDINGER/HEISENBERG:ballener-kenchi
7. JAMES CHADWICK:comaling-bautista
1. DEMOCRATUS: PAGANTUPAN-ALEXA NICOLE
2. JOHN DALTON: RUSSEL JOHN MANLA HILARDES
3. JJ THOMPSON: RICKSON-COMPASION
4. ERNEST RUTHERFORD: MALITOC-GAMAY
5. NEILS BOHR: CANONO-LIGASAN
6. SCHROEDINGER/HEISENBERG: JEFERSONAGIMLOD, R.
7. JAMES CHADWICK:SIBAYAN-CAPUNGAS
assignment
1-2) What are quarks?
3-8) What are the “flavors” of quarks?
9-10) Why quarks have “flavors?”