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Matter
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Anything that has mass and takes up
space.
All matter can be measured
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Mass
Volume
Density
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Hundreds of years
ago, scientists
found that certain
types of matter
couldn’t be
broken down into
any other simpler
substances
They called these
special pure
substances:
 elements
No matter how small you divide it,
gold is only made of gold atoms.
So what is an atom?
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The smallest particle an element can be
divided into and still maintain the
properties of that element.
Atoms are the building blocks of all matter.
Why learn about atoms?
All matter is made of atoms, atoms are the basic
building block of everything in the universe
What does an atom look like?

The model of the structure of the atom
has changed as technology has improved
and as more evidence has been gathered.
What are these made of?
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 he called
ATOMA
(greek for indivisible)
First atomic models – roughly
based on earth, air, water, and fire
What’s new?
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
The new model of an atom- a tiny
solid sphere
What’s new?
HISTORY OF THE ATOM
1898
Joseph John Thompson
found that atoms could
sometimes eject a far smaller
negative particle which he
called an
ELECTRON
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
The new model of an atom- atoms
contain smaller, negatively charged
particles
What’s new?
1910
Ernest Rutherford
• English scientist who tested JJ Thompson’s model
• 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. This held the electrons in place by
electrical attraction
Rutherford’s experiment
His hypothesis:
The
results?
The new atomic model- a dense,
positively charged nucleus in the
center surrounded by electrons
What’s new?
1913
Niels Bohr
studied under Rutherford in
Manchester, England
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
The new atomic model- electrons
are in orbits around the nucleus at
different energy levels
What’s new?
1920’s
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Electron Cloud Model
 Electrons surround the positively
charged nucleus, but not in set orbits
 They are in different levels, or clouds
 There are set amounts of electrons
found in each cloud
The new atomic model- set
numbers of electrons are found in
different cloud layers
Exit Slip
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Choose one of the atom models
Draw a picture of it
Label it with the name of the model
Give the date of when this model was first
described
Give a name to the chemist who described
it
Your name on the back
Atomic Model History
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http://www.youtube.com/watch?v=QbWK
F9uDF7w
http://www.youtube.com/watch?v=thnDx
FdkzZs
ATOMS AND ATOMIC
STRUCTURE
Atom Nucleus Proton Neutron
Electron
WHAT IS AN ATOM?
o
o
The smallest unit
of an element.
Consists of a
central nucleus
surrounded by one
or more electrons.
WHAT IS THE NUCLEUS?
o
o
o
The central part of
an atom.
Composed of
protons and
neutrons.
Contains most of
an atom's mass.
WHAT IS A PROTON?
o
o
Positively
charged particle.
Found within an
atomic nucleus.
WHAT IS A NEUTRON?
o
o
Uncharged
particle.
Found within an
atomic nucleus.
WHAT IS AN ELECTRON?
o
o
Negatively
charged particle.
Located in shells
that surround an
atom's nucleus.
Summary
Particle
Charge
Mass (amu) Location
Proton
positive
1
nucleus
Neutron
neutral
1
nucleus
Electron
negative
<1
shells
outside the
nucleus
Atoms as Pictured on the Periodic Table
Atomic Number
Symbol
Name
Atomic Mass
protons
electrons
Atomic number equals the number of ____________
or ___________.
neutrons
protons
Atomic mass equals the number of ______________
+ ____________.
(mass number)
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How many protons?
 Same as the atomic number
How many electrons?
 Same as the atomic number
How many neutrons?
 Number of protons + ? = Atomic Mass
Atoms are neutral

Since protons (positive charge) are
equal to the numbers of electrons
(negative charge), the overall charge
of an atom is neutral
Video of particles
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http://www.youtube.com/watch?v=lP57gE
WcisY
Bill Nye
http://www.youtube.com/watch?v=aNK1
mQfNeik
Let’s review
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The Atomic Number of an atom = number
of ______________
Protons or electrons in the nucleus.
The Atomic Mass of an atom = number
Protons
+ _________
neutrons
of _________
in the
nucleus.
The number of Protons = Number of
____________.
electrons
Electrons

_____________
orbit the nucleus.
http://www.bbc.co.uk/newsround/22369468
Periodic Table blocks can
sometimes contain even more
information!