Download Unit 3 The History of the ATOM

Schrodinger
Bohr
Rutherford
+
Thomson
Democritus &
Dalton
Unit 3
The History of the ATOM
and Atomic Structures
+
Democritus 460-370 B.C.

Greek Philosopher

He called nature’s basic particle an
atomos, based on the Greek word
“indivisible.”

Had no evidence, so people didn’t
take him seriously.

He considers education to be the
noblest of pursuits, but cautioned that
learning without sense leads to error.
(THERE MUST BE A POINT!!!)

Aristotle said empty space did not
exist & rejected Democritus; said
matter was EARTH, WATER, AIR &
FIRE
+ John Dalton 1803
Dalton’s Atomic Theory
1.
All elements are composed
of tiny indivisible particles
called atoms.
Element
A
2. Atoms of the same element
are identical. The atoms of
any one element are different
from those of any other
elements.
+ Dalton’s Atomic Theory
3. Atoms of different elements can physically
mix together or can chemically combine
with one another in simple whole-number
ratios to form compounds.
+ Dalton’s Atomic Theory
4. Chemical reactions occur when atoms
are separated, joined, or rearranged.
Atoms of one element, however, are
never changed into atoms of another
element as a result of a chemical
reaction.
+ J.J. Thomson 1897 (with
Crookes & Millikan)
 discovery of the electron (e-)
disproved
Dalton’s theory; atoms DID have
smaller parts after all
Used
a cathode ray tube to prove that
there were charged particles (stream of (-)
particles) within the atom
+
Thomson Model
Plum pudding model
aka chocolate chip
cookie model
Millikan found out
that electrons
were negatively
charged and had a
mass of 1/1840 of
a hydrogen atom
+
Video Links to Experiments

JJ Thomson’s Cathode Ray Tube
How does it work?

Rutherford’s Gold Foil Experiment
What did he do?
+
Ernest Rutherford 1911
 Used
alpha particles to shoot
at gold foil. Got unexpected
results. Something was
deflecting particles back to
the source.
 Buried
next to Sir Issac
Newton and Lord Kelvin in
Westminster Abbey.
+
Empty Space
Nucleus
Electrons
Rutherford
said,
+
“Atoms have a nucleus!”
Dense
& positively charged
Contains
most of the mass of the atom
Contains
the protons (positive charge;
heavy)
Electrons
are around the outside of the
nucleus flying around the empty space
+
Video Links to Experiments

JJ Thomson’s Cathode Ray Tube
How does it work?

Rutherford’s Gold Foil Experiment
What did he do?
+
James Chadwick
 Discovered
 Has
the neutron in 1932
a neutral charge
 Found
in the nucleus
 About
½ of the mass of the nucleus
 Wanted
to know where the extra mass was
coming from in an atom; shot particles @
beryllium
 Eventually
led to experiments to bombard
atoms with neutrons –> uranium  bombs!
+
Niels Bohr - 1913
Created
the Bohr model
Electrons
travel in definite orbits/
energy levels around the nucleus
aka “Planetary
Model” – orbit the nucleus
like planets around the sun
Electrons
have fixed amounts of energy
“quanta”
 Low
energy  closer to nucleus
 High energy  further from nucleus
+ Bohr Model
+
Werner Heisenberg, 1927
It’s
impossible to know
both the location and the motion
of an electron at the same time
Heisenberg
Uncertainty Principle
+ Quantum Mechanical Model
(aka wave mechanical model)
Erwin
Schrodinger – 1926
Electrons
Electrons
DO NOT orbit the nucleus
DO have quanta of energy that
determine placement in an atom
+
Electron Cloud
Area
where there is a high probability
that the electron will reside there 90%
of the time
+
Schrodinger’s Cat
+
+
+
Subatomic
Particles
+
Electron Cloud
- electrons
-
o +
+ o
-
Nucleus
- protons
- neutrons
+
+
p
0
n
Found in the nucleus
Found in the nucleus
Mass = 1 (amu)
Same mass as a proton
Relative charge = +1
Mass = 1 amu
Relative charge = 0
e
Found in the electron
cloud around the
nucleus
Mass 1836 times
smaller than a
proton
Therefore, mass
doesn’t really count!
(0.0005 amu)
Relative charge = -1
+
Atomic Number
 Atomic
Number Z = p+
18.99
the number of protons in the nucleus
 ALL
atoms of the
 SAME element have the
 SAME atomic number and
 SAME protons
In a neutral atom,
+
p
PROTONS
IDENTIFY
THE ELEMENT!
=
Magnesium = Z = 12
12 protons
e
+ Mass
Mass
Number (nucleus!)
number = p+ + n0
(electrons don’t have much mass!!!)
Z = 82  LEAD, Pb
Protons?
82
Electrons?
82
Mass 207
Neutrons?
125
#n0 = MN - # p+
= 207 – 82
= 125 neutrons
+
An element has an atomic number of 6
and a mass number of 14.
 What is the element? Z = 6 CARBON
 How many neutrons?
MN = 14
#n = MN – #p+
= 14 – 6
= 8 neutrons
+ Group number (column)
the second digit tells us the
number of valence (outer)
electrons in a Bohr atom
Period number (row)
the number of energy
levels outside of the
nucleus
17
2
Average atomic mass
(not the mass #)
18.99
+
Bohr model of the atom
(protons & neutrons)
Yep! Somebody lied when they
told you 8! We’ll go into details in
Unit 4. Hold your horses…
+
Identify this atom:
(assuming it is neutral p+ = e-)
NUCLEAR NOTATION
16
8
O
HYPHEN NOTATION
Oxygen - 16
+
If we drew a Bohr model of sodium:

How many protons?

How many neutrons?

How many energy levels?

How many electrons?
23
Na
+
Scanning Electron Microscopes

http://www.youtube.com/watch?v=egPQZw0QkVw