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Transcript
Alchemy
A Particulate World – Part I
Day 9
Catalyst – 9/21 (page 14)

What are the five models of atomic
theory? (in order)
Agenda


Reminders
Dead Chemists Lecture


Graphic Organizer Time Line Guided Notes
Pudding In The Clouds Activity
Early Theories of Matter
Ancient Greeks: All matter consists of 4 elements:
Earth, Air, Water, & Fire
Take notes on the Time Line Graphic Organizer
Cast of Characters








New
atomic
Model


1. Democritus
2. Lavoisier
3. Proust
4. John Dalton
5. J.J. Thomson
6. Ernest
Rutherford
7. James Chadwick
8. Niels Bohr
9. Robert Millikan
10. Ernst
Schrodinger
Democritus (2400 years ago)

Greek philosopher (470380 B.C.)



Atomos - “indivisible”.
The universe was made
up of atoms.

Small & indestructible
Antoine Lavoisier (1743 1794)


Law of
Conservation of
Mass - 1774
Father of Modern
Chemistry
Joseph Proust

The Law of Definite
Proportions
(composition) - 1808

In any compound
the elements are
present in a fixed
proportion by
weight.
John Dalton (1766-1844)


Atomic Theory
Law of Partial
Pressures!
Dalton’s Atomic Theory
Wrong!
Wrong!





Elements are made of tiny particles called atoms that are
indivisible..
All atoms of a given element are identical.
The atoms of a given element are different from those of any
other element.
Atoms of one element can combine with atoms of other
elements to form compounds. A given compound always has
the same relative numbers and types of atoms.
Atoms are indivisible in chemical processes. That is ,atoms are
not created or destroyed in chemical reactions. A chemical
reaction simply changes the way the atoms are grouped
together.
J.J. Thomson (1856-1940)


Discovered
electrons
(cathode ray
tube
experiment)
Developed
“plum pudding”
atomic model
Thomson’s Cathode Ray Tube
Experiment



Results: The discovery of the electron! Atoms are
divisible!
A CRT is an empty glass tube that has an electric
current passed through it.
Thomson proposed that the mysterious rays in the
tubes were pieces of atoms!
Remember –
up until this point,
the atom was it!
No protons, neutrons,
electrons, quarks, etc.
Thomson’s Plum Pudding
Model

Wrong!

Wrong!


The atom is divisible!
Electrons are
suspended in a
positively charged
electric field
Mass of atom due to
electrons
Atom mostly "empty"
space compared size
of electron to size of
Ernest Rutherford (18711937)


Gold foil experiment
Rutherford’s atomic
model



Discovered the
nucleus
Atom is mostly space
Mass is concentrated
in a positively
charged nucleus
(sort of discovered
protons)
Rutherford’s Gold Foil
Experiment




He bombarded a thin gold foil
with alpha particles (He atoms).
Although almost all of them went
through the gold, 1 in 8000
would "bounce" back.
Rutherford said that it was "as if
you fired a 15-inch naval shell at
a piece of tissue paper and the
shell came right back and hit
you."
He concluded that the atom's
mass is concentrated in a small
positively-charged nucleus and
the electrons inhabit the farthest
reaches of the atom.
James Chadwick (1891-1974)
I discovered
the neutron!
And isotopes!
There are
protons and
neutrons in
Rutherford’s
nucleus!
Niels Bohr (18851962)

Wrong!

If electrons are
stationary, they
would fall into the
positively-charged
nucleus!
The electrons must
be moving in planetlike orbits around
the nucleus!
Bohr’s Atomic Model


Electrons orbit in paths
around nucleus
By assuming electrons
orbited in circles with
disscrete radii, Bohr could
explain the discrete
wavelengths in the
emission spectrum of H.

Big Problem: It only
worked for hydrogen!
Wrong!
More on the Bohr Model


The energy level is the region around
the nucleus the electron is likely to be
moving.
Quantum theory – a quantum of energy
is the amount of energy required to
move an electron from one energy
level to another.
Robert A. Millikan (1868-1953)


Millikan found the
charge of an
electron through his
famous oil drop
experiment.
An electron has a
charge of 1.602 x
10-19 coulombs.
Millikan’s Oil Drop Experiment



Oil droplets were
sprayed into a small
hole in a box with a
metal top and bottom.
The metal was
electrified, causing the
oil droplet to be
suspended in midair.
The voltage, speed, and
mass of the droplet was
used to calculate the
electric charge of the
electron.
Ernst Schrodinger (18871961)

Developed the quantum
mechanical model of
the atom



Can only calculate the
probability of finding an
electron in a certain
position around the
nucleus (energy levels).
Electron clouds are most
dense where the
probability for finding an
electron is high.
Particles behave like
waves.
Antiquity

Ancient Model
through John Dalton
JJ Thomson

Plum Pudding Model
Rutherford

The nuclear or “nut”
model.
Bohr

Planetary Model
Schrodinger

Quantum
Mechanical Model
The Structure of the Atom
The Billiard Ball Model
Plum Pudding Model
Nuclear Atom
Bohr Model
Electron Cloud
(Quantum Mechanical
Model)
An Atom
Day 10

Isotopes and Building Atoms
Subatomic Particles
Charge
Location
Mass
0
Nucleus
1 amu
Proton
+1
Nucleus
1 amu
Electron
-1
Outside
nucleus
1/2000
amu
Neutron
(electron cloud)
Nucleus: Atom
Marble: Stadium
All about the atom






All neutrons are identical
All protons are identical
Electrons are identical, but have
different energy levels
The nucleus is dense
The electron cloud is mostly empty
space
In a neutral atom (not an ion):
# of electrons = # of protons
Atomic Number
• The number of protons in the nucleus
of an atom is called the atomic number.
• Protons are what define an atom of an
element.
• So what is going on here?
Hydrogen
Hydrogen
(Deuterium)
Hydrogen
(Tritium)
Mass Number of an Atom



Mass Number = # Protons + #
Neutrons
Carbon-12 has 6 neutrons and 6
protons, so its mass number is 12 amu.
Electrons have a teeny-tiny mass so
they are not included in the mass
number!
What does “Carbon-12” mean?
Building Atoms

Complete building atoms activity
Questions 1 – 10 found on page 48 of
your Alchemy Workbook.

Complete on page 16 of your Classwork NB
The Convenient Atomic Mass
Unit


1 amu = 1.67 x 10-24 g
How did we get it?

1 amu = 1/12 the mass of 1 C-12 atom.
Isotopes

An atom that has the same number of
protons but a different number of neutrons
is an isotope.
Example:
 Carbon will always have 6 protons, but the
number of neutrons can change.



Carbon-12 (6 protons + 6 neutrons)
Carbon-13 (6 protons + 7 neutrons)
Carbon-14 (6 protons + 8 neutrons)
Isotopes

Lithium-7



3 protons
4 neutrons
The 3 protons in the
nucleus are what
make this atom
Lithium!
7
3
Li
Remember: Atomic # = # of protons
Another Isotope Example


ALL Bromine atoms
have 35 protons.
Some have:






41
42
44
46
47
48
neutrons
neutrons
neutrons
neutrons
neutrons
neutrons
Mass #
Atomic #
Br
How would you find the
number of neutrons?
Atomic Mass


Atomic mass (weight) is the weighted
average of the mass numbers of the
isotopes of an element.
Carbon’s average atomic mass is 12.01
Fill in the table!
Symbol
Atomic
#
He
2
Mg
12
Br
Al
Mass # # Protons # Neutrons # Electrons
4
12
80
35
13
14
How did you do?
Symbol Atomic # Mass # # Protons # Neutrons # Electrons
He
2
4
2
2
2
Mg
12
24
12
12
12
Br
35
80
35
45
35
Al
13
27
13
14
13
Ions

To be stable, some atoms will gain or
lose electrons and become IONS.


Cations are positively charged (lose
electrons)
Anions are negatively charged (gain
electrons)
Lithium loses one electron to become Li+
Chlorine GAINS one electron to become Cl-