Download Atomic Structure and Notes_AISD ppt

S.MORRIS 2006
Papercuts
• This piece of paper is 28cm x 2.5 cm
• How many times would you have to cut this
piece of paper to be the same width as an atom?
• Once you cut a piece in half, you have to discard
one half and then use the other piece to
continue this process
• Repeat this until you can no longer cut the
paper.
• How many cuts did you make?
Width of an Atom
• The average width of an atom is 130
picometers
• 1pm = 10-12 m = 1/1 000 000 000 000 of a
meter
• 1 millimeter = 1 000 000 000
picometers
• That’s teeny tiny !
Who are these dead dudes?
How did they
contribute to our
present day model
of an atom?
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)
This theory was ignored and
forgotten for more than 2000
years!
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 Theory
1. all elements are
composed of atoms.
2. atoms of the same
element are exactly alike.
3. atoms of different
elements are different.
Dalton’s Atom
4. compounds are formed by
the joining of atoms of two
or more elements.
Fill this in on your Notes
sheet
HISTORY OF THE ATOM
1898
Joseph John Thompson
found that atoms could sometimes eject a far
smaller negative particle which he called an
ELECTRON
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
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.
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.
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 Atomic Theory
The Bohr model was a modification of the
Rutherford model.
Bohr the electrons in certain circular orbits
around the nucleus called shells.
+
Scientists had learned a lot
about the atom, but couldn’t
figure out what made it so
heavy. In 1932 James
Chadwick solved the mystery
by coming up with the idea of
neutrons, neutral particles that
live in the nucleus with protons.
The new improved Bohr model
includes these particles.
0
Neutrons
New Bohr Model
Bohr Model of a HELIUM ATOM
Shell
proton
+
electron
N
N
+
-
neutron
ATOMIC STRUCTURE
Particle
Charge
Mass
proton
+ charge
1 amu
neutron
No charge
1 amu
electron
- charge
nil
Use your periodic table to help you find the
ATOMIC STRUCTURE
2
He
4
Atomic number
the number of protons in an atom
Atomic mass
the number of protons and
neutrons in an atom
Charge = # of protons + # of electrons
= (+ number) + (- number)
If the number of protons is the same as the number of
electrons, what is the charge of the atom?
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 8 electrons
Nucleus
1st shell
2nd shell
3rd shell
Adapted from http://www.sciencespot.net/Media/atomsfam.pdf
So let’s try it….
• How to draw a Lithium atom
• First, look at the Periodic Table
• Second, How do you find the number of
protons?
• Then determine the number of neutrons
• Then determine the number of electrons
3
Li
Lithium
7
Created by G.Baker
www.thesciencequeen.net
So let’s try it….
Protons = 3
3
-
Li
+
+
+
-
Lithium
-
7
Electrons = 3
Neutrons = 4
2 in the 1st shell, 1 in the
2nd shell
(7-3=4)
Created by G.Baker
www.thesciencequeen.net