• Name a scientist that you remember and
tell for what he/she is known, did, or
discovered. Give any other information
you can such as branch of science, prizes
won, country of origin, etc.
Atomic Structure
Defining the Atom
Eureka - Atoms
Meet the Elements Video clip
What is an Atom?
The smallest part of an element that retains its identity in a
chemical reaction.
Atomic History
• http://www.youtube.com/watch?v=VQfOlM
s4zFs&feature=related
HISTORY OF THE ATOM
460 BC
Democritus develops the idea of atoms
he pounded up materials in his pestle and
mortar until he had reduced them to smaller
and smaller particles which could not be
divided and called these:
ATOMA
(greek for indivisible)
Historic Models of the Atom
• Aristotle (384-322 BC) didn’t think there
was a limit to the number of times matter
could be divided.
• He knew there were small particles. Air,
Fire, Earth, Water
HISTORY OF THE ATOM
1808
John Dalton
suggested that all matter was made up of
tiny spheres that were able to bounce around
with perfect elasticity and called them
ATOMS
Dalton’s Atomic Theory
1. All elements are composed of atoms (which
can’t be divided).
2. Atoms of the same element have the same
mass and atoms of different elements have
different masses.
3. Compounds contain atoms of more than one
element.
4. In a compound, atoms of different elements
always combine in the same way.
Dalton’s atom
Dalton’s Atomic Theory
Most of Dalton’s statements are now known
to be flawed.
As we continue to study the atom, we will
talk about discoveries that disproved
Dalton’s statements.
Scientists have revised the theory due to
new discoveries!
HISTORY OF THE ATOM
1898
Joseph John Thomson
found that atoms could sometimes eject a far
smaller negative particle which he called an
ELECTRON
J.J. Thomson, 1897
•
•
Discovered the electron, the subatomic particle
with a negative charge
His experiments involved the use of a cathode
ray tube
Animation of
Thomson’s model
JJ Thomson Question and
explanation on youtube
• http://www.youtube.com/watch?v=XU8nM
KkzbT8
JJ Thomson Video clip
• Start at 5:00 and go to about 7:00
HISTORY OF THE ATOM
1904
Thompson develops the idea that an atom was made up of
electrons scattered unevenly within an elastic sphere surrounded
by a soup of positive charge to balance the electron's charge
like plums surrounded by pudding.
PLUM PUDDING
MODEL
Thomson’s Atomic Model
• Developed the Plum
Pudding model.
(think of a chocolate
chip cookie)
• Electrons evenly
distributed throughout
a positively charged
material.
Plum Pudding Model
Sphere of
Positive charge
e-
e-
eee-
HISTORY OF THE ATOM
1910
Ernest Rutherford
oversaw Geiger and Marsden carrying out his
famous experiment.
they fired Helium nuclei at a piece of gold foil
which was only a few atoms thick.
they found that although most of them
passed through. About 1 in 10,000 hit
HISTORY OF THE ATOM
helium nuclei
gold foil
helium nuclei
They found that while most of the helium nuclei passed
through the foil, a small number were deflected and, to their
surprise, some helium nuclei bounced straight back.
Ernest Rutherford, 1911
• Tested theory that electrons were evenly
distributed throughout the atom within
positively charged material
• Performed the Gold-Foil Experiment
Rutherford animation
Another Rutherford Animation
Ernest Rutherford
• If Thomson’s model was correct, most of
the alpha particles should pass through
with a little deflection
Rutherford’s Model
• Proposed that atoms contain a nucleus, a
small, dense, positively-charged sphere in
the center of the atom.
• Atom contains mostly empty space.
• The nucleus is tiny compared with the
atom as a whole.
Ernest Rutherford
Thomson’s model
Rutherford’s model
Rutherford’s model:
Nuclear Atom
e-
e-
+
+ +
e-
Rutherford did
NOT know about
neutrons!
HISTORY OF THE ATOM
Rutherford’s new evidence allowed him to propose a more
detailed model with a central nucleus.
He suggested that the positive charge was all in a central
nucleus. With this holding the electrons in place by electrical
attraction
However, this was not the end of the story.
• The Houston
Astrodome occupies
more than nine acres
and seats 60,000
people.
• If the stadium were a
model for an atom, a
marble could
represent its nucleus!
Development of the Atomic Theory
Outline Activity
HW- please work on page 1 of the Atom
Worksheet and your Atomic Theory
Outline/Foldable
Development of the Atomic Theory
Timeline Activity – DAY 2
• Show me your timeline!!!
• Let’s review those great scientists!!
Comparing Dalton, JJ Thomson,
and Rutherford
This is a one question quiz on youtube….
HISTORY OF THE ATOM
1913
Niels Bohr
studied under Rutherford at the Victoria
University in Manchester.
Bohr refined Rutherford's idea by adding
that the electrons were in orbits. Rather
like planets orbiting the sun. With each
orbit only able to contain a set number of
electrons.
Bohr’s Atom
electrons in orbits
nucleus
Summary
• Dalton’s Theory- all matter is made up of
atoms, which can’t be divided
• Thomson’s Model- discovered atoms were
made up of smaller particles (these
smaller particles are charged)
• Rutherford’s Theory- discovered the
positively charged nucleus
Parts of an Atom
• Atom = nucleus surrounded by one or more electrons
• Atoms are neutral (no charge)
– same number of protons as electrons.
• Majority of the atom is empty space.
– If nucleus were the size of a pencil eraser, the closest electron would be
100 yards away!
• Subatomic Particles
– Protons (+)
– Neutrons (0)
– Electrons (-)
• Nucleus: Tightly packed
Protons & Neutrons
• Electrons Orbiting nucleus
@ speed of light!!
HELIUM ATOM
Shell
proton
+
-
N
N
+
electron
What do these particles consist of?
-
neutron
ATOMIC STRUCTURE
Particle
Charge
Mass
proton
+ charge
1
neutron
No charge
1
electron
- charge
nil
Atomic Number
• Atomic Number = # of Protons
• Each Element in the Periodic Table has a
different number of Protons, therefore each
element has a different, unique, atomic number.
When reading the Periodic
table notice each element has
a unique 1 or 2 letter symbol
and “big” & “small” number
listed
Eureka - Electrons
ATOMIC STRUCTURE
He
2
4
Atomic number
the number of protons in an atom
Atomic mass
the number of protons and
neutrons in an atom
number of electrons = number of protons
Can you read these?
Atomic Number and Mass Activity
Contents of each box
• Draw a box for your
chosen element from
your atom project and
explain in detail what
each of these are!!
Atomic number
Symbol
Element name
Atomic mass
Electrical Atomic Charge
• Remember that Atoms are neutral (no charge)
• So, the # of protons = # of electrons
• If you know the Atomic #, you know the # of
Protons and also the # of Electrons!!
For example:
Carbon has an atomic # of 6, it therefore has 6 Protons which
has an electrical charge of +6, to make the atom neutral we
need 6 negative charges found in the 6 electrons orbiting the
nucleus.
Mass number (atomic mass)
Atomic Mass = the total # of Protons & Neutrons
( we don’t worry about the mass of the electrons
since they have almost no mass)
How many Neutrons are there?
• Remember:
– The Atomic # = the # of Protons
– The Atomic mass = The # of both Protons & Neutrons.
– Therefore, if you subtract the Atomic # (the number of Protons)
from the Atomic mass (the number of both Protons & Neutrons)
what is left over must be the number of Neutrons!!
For Example w/ Carbon:
Atomic Mass-Atomic # = # Neutrons
Atomic Mass = 12,
Atomic # 6
12 – 6 = 6
Therefore there are 6 neutrons
present in the Carbon nucleus
If you don’t believe
me… just count for
yourself.
What is an Isotope?
Atoms with the same
number of protons, but a
different number of
neutrons.
“Same number of protons”
means same atomic
number, which means
same element.
“Different number of
neutrons” means different
mass numbers.
Isotopes
• Can sometimes be represented with
dashes and numbers that follow the
element.
•
•
•
•
C-14
Pu-246
O-16
O-17
Heavy Water
• Video clip
• Information about heavy water
Element Symbol Quiz
• You need to know the element symbol for
the following elements:
– 1-20
– 24-30
– 35,47,50,53
– 79,80,82,86,88
• You will have a quiz on _____________
• I will give you the symbol or the name and
you will have to give me the other…there
will be NO WORD BANK!
Review
• How many protons and neutrons are there
in an atom of 115B?
A 5 protons and 6 neutrons
B 5 protons and 11 neutrons
C 11 protons and 5 neutrons
D 11 protons and 6 neutrons
• How many neutrons are in an element of
Pu-246?
– A. 94
– B. 150
– C. 152
– D. 246
• What are Oxygen-17 and Oxygen-18?
• How many protons do they each have?
• How many neutrons do they each have?
Neils Bohr, 1913
• From a study of Hydrogen, concluded that
an electron travels around the nucleus in
circular paths called orbits
• Each pathway represents an energy
level.
• Only orbits of certain energies are allowed.
Electrons can’t exist between orbits.
• Like rungs on a ladder
Bohr’s model animation
Niels Bohr
• Level closest to nucleus has lowest energy
• Energy must be added for an electron to move up a
level. Energy is released when an electron moves
down.
ATOMIC STRUCTURE
Electrons are arranged in Energy Levels or
Shells around the nucleus of an atom.
•
first shell
a maximum of 2 electrons
•
second shell
a maximum of 8 electrons
•
third shell
a maximum of 18 electrons
Bohr’s Planetary Model – looks like
planets orbiting the sun!!!
How many electrons are present in each orbit?
2
8
18
32
Electron Cloud Model – advanced
from Bohr’s model
• Bohr’s “orbits” are now “principal energy levels”.
• Bohr was incorrect in assuming that electrons moved like
planets in a solar system.
• The Electron Cloud model shows the MOST LIKELY
location of electrons in an atom!! (these are not precise
since it’s all based on probability!!)
– Think of a propeller on an airplane...you can see the blades
when they aren’t moving…when it is moving you see only a
blur…this is like the electron cloud model!!
• The number of electrons in each principal energy level is
still correct
• 2, 8, 18, 32
• More atoms shown with Bohr’s model
• Which of the following provides the best
analogy for an electron in an atomic
orbital?
• a. a bee buzzing from flower to flower in a
garden
• b. a bird flying high in the sky
• c. an ant crawling on the surface of a leaf
• d. a bee buzzing inside a closed jar
Quantum Mechanical Model
(electron cloud model)
Bohr Model
Atomic Orbitals
• Orbital – a region of space around the
nucleus where an electron is most likely to
be found (think of a map of the school and
dots that mark your location every 10
minutes)
• Electron configuration – the arrangement of
electrons in the orbitals of an atom
– Most stable – electrons are in orbitals with the
lowest possible energy
Remember!!
• When electrons move to a higher orbital
they GAIN energy!!
• When electrons move to a lower orbital
they RELEASE energy!!
Structure of the Atom
subatomic
particles
Proton p+
Positive charge
In nucleus
mass =1
Neutron no
Neutral charge
In nucleus
mass = 1
Electron eNegative charge
In electron cloud
mass = 1/1840
Electron Cloud Models
• Please draw electron cloud models (Bohr
models) for these elements: (please make sure you
show # of protons and neutrons as well!!)
– Oxygen or Argon
Now:
• Assign Atom’s Project – put a Bohr Model
in your composition book
• Work on Atomic Mass worksheet
• Work on Atom’s worksheet
• Take notes on Periodic Table
• Elementary My Dear Watson
History of Atomic Structure
Video clip