Early Models of the Atom
History of the Atom
Standard Atomic Notation
Some Intro Songs for your entertainment:
The Atom Song: http://www.youtube.com/watch?v=vUzTQWn-wfE&NR=1 (3 min)
HISTORY OF THE ATOM
460 BC
Democritus develops the idea of atoms
- ancient Greek philosopher
-suggested that matter was made up of tiny
particles called:
ATOMOS
(greek for indivisible)
- his theory was not accepted for 2000 years
HISTORY OF THE ATOM
1808
John Dalton
- working with gases, reconsidered Democritus’
theory that particles are indivisible
- Described matter as tiny spheres that were
able to bounce around with perfect elasticity
and called them:
ATOMS
History of the Atom
Dalton’s Atomic Model:
1) All matter is made up of atoms, which are particles
too small to see
2) Each element has its own kind of atom, with its own
particular mass
3) Compounds are created when atoms of different
elements link to form molecules
4) Atoms cannot be created, destroyed, or subdivided
in chemical changes
Problem with Dalton’s Theory:
– unable to explain the Electrical nature
of matter:
Like charges repel
Unlike charges attract
History of the Atom
1879
William Crookes
- worked with cathode ray tubes
- beam of particles was attracted to a positive
plate
- these particles were called:
ELECTRONS
- have a negative charge
History of the Atom
1886
Eugen Goldstein
-most samples of matter are NOT charged
-the atom must contain positively charged particles
-used cathode ray tubes to prove this and they were
called:
PROTONS
HISTORY OF THE ATOM
1898
Joseph John Thompson
- atom had a positive core and electrons were
embedded in this
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
Or
RAISIN BUN
MODEL
HISTORY OF THE ATOM
1910
Ernest Rutherford
- designed an experiment using RADIUM (this
element spits out positive ALPHA particles)
- he placed a piece of gold foil in front of the
beam, surrounded by a screen to detect the
path of the particles
- 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 particles passed through
the foil, a small number were deflected and, to their surprise,
some particles bounced straight back.
Rutherford’s Gold Foil Experiment
Rutherford & Bohr (4 min)
http://videos.howstuffworks.com/hsw/25133-icons-of-science-bohr-and-the-structure-of-the-atom-video.htm
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 the central
nucleus. This held the electrons in place by electrical
attraction, so the electrons swarm around the nucleus.
However, this was not the end of the story.
History of the Atom
1932
Chadwick
- Nucleus contains another particle which
has NO charge (neutral) called a:
NEUTRON
- This particle and the proton have approximately the same mass,
but the electron is very small. It takes 1837 electrons to have
the same mass as ONE proton or neutron.
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
HELIUM ATOM
Shell
proton
+
-
N
N
+
electron
What do these particles consist of?
-
neutron
ATOMIC STRUCTURE
Subatomic
Particle
Location
Charge
Mass
Protons
In nucleus
Positive
1
Neutrons
In nucleus
Neutral
1
Electrons
Orbit around negative
nucleus
None
(1/1837)
STANDARD ATOMIC NOTATION
4
He
2
Mass number
the number of protons and
neutrons in an atom
Atomic number
the number of protons in an atom
Atomic number = number of electrons = number of protons
mass number – atomic number = number of neutrons
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
•
fourth shell
assume up to 8 electrons
ATOMIC STRUCTURE
There are two ways to represent the atomic
structure of an element or compound;
1.
2.
Electronic Configuration
Bohr-Rutherford Diagrams
ELECTRONIC CONFIGURATION
With electronic configuration, elements are represented
numerically by the number of electrons in their shells
and number of shells. For example;
Nitrogen
2 in 1st shell
5 in
2nd
shell
configuration = 2 , 5
2
+
5 = 7
14
7
N
ELECTRONIC CONFIGURATION
Write the electronic configuration for the following
elements;
40
a)
20
23
Ca
b)
11
2,8,8,2
35
d)
17
Na
2,8,7
c)
8
2,8,1
28
Cl
16
e)
14
O
2,6
11
Si
2,8,4
f)
5
B
2,3
SUMMARY
1. The Atomic Number of an atom = number of
protons in the nucleus.
2. The Atomic Mass of an atom = number of
Protons + Neutrons in the nucleus.
3.
The number of Protons = Number of Electrons.
4.
Electrons orbit the nucleus in shells.
5.
Each shell can only carry a set number of electrons.
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