Model: A FAMILIAR idea used to explain UNFAMILIAR facts and
PHENOMENA.
Theory: An EXPLANATION of
OBSERVABLE facts and
PHENOMENA.
To remain valid, models and
theories must:
- EXPLAIN all known FACTS
SCIENTIST to make
correct PREDICTIONS
Democritus: (400 B.C.)
- proposed the EXISTENCE of an
ATOM
GREEK word “ATOMOS” which means
NOT TO CUT or “indivisible”
Aristotle
- REJECTED the idea of the ATOM
-said MATTER could be CUT CONTINUALLY
Dalton’s theory proposed that atoms (1803):
-are BUILDING BLOCKS of MATTER
-are INDIVISIBLE
-of the SAME ELEMENT are IDENTICAL
-of DIFFERENT ELEMENTS are DIFFERENT
-UNITE in SMALL, WHOLE NUMBER ratios to form
COMPOUNDS
J.J. Thomson (1896)
-credited with DISCOVERY of ELECTRON: a blow to DALTON’S
INDIVISABLE atom
-proposed the PLUM PUDDING model of the atom: NEGATIVELY
charged electrons embedded in a ball of POSITIVE CHARGE
Rutherford’s Gold-foil Experiment: (1909-Planetary Model-
1909)
-aimed ALPHA PARTICLES at GOLD FOIL
- MOST passed THROUGH
- a FEW particles were DEFLECTED
- SOME particles even BOUNCED BACK
Conclusions of Rutherford's experiment:
-MOST of the ATOM is EMPTY SPACE
- DENSE POSITIVELY charged CORE(NUCLEUS)
The Chemistry Quiz
CR1. D CR2. B 1. B 2. C
3. D
4. C
5. B
http://micro.magnet.fsu.edu/electromag/java/rutherford/
The only change in Dalton's theory today is to change the word
mass to "average mass".
Dalton also developed the law of Definite Proportion which states
that the ratio of masses of one element that combine with a
constant amount of another element can be expressed in small
whole numbers.
Cathode Ray Tube
In the mid 1800's the cathode ray tube was used to investigate the
atom.
The positive terminal is called an
Anode.
Its negative terminal is called a
Cathode.
http://www.dlt.ncssm.edu/core/c3.htm
The rays that appeared in the tube were called Cathode Rays.
J.J. Thomson used the cathode ray tube to discover the electron.
He calculated the mass to charge ratio of the electron. The sign
of the charge on an electron is
negative(-). The symbol e- is
used for an electron.
http://chemed.chem.purdue.edu/demos/main_pages/6.1.html Crooke’s tube
http://www.chem.uiuc.edu/clcwebsite/cathode.html Cathode ray tube (J.J. Thomson)
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf
Rutherford/Thomson models
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf
Rutherford’s model
Oil drop
Millikan determined the charge on the
electron with his OIL DROP experiment.
Video http://cwx.prenhall.com/bookbind/pubbooks/petrucci8/medialib/media_portfolio/02.html
The positive PROTON was also discovered using a cathode ray
tube. The proton is 1832 x the mass of the electron.
ISOTOPES
J.J. THOMSON also discovered isotopes. Isotopes are
atoms of the same element with the same number of
PROTONS but a different number of NEUTRONS.
MOSELEY determined the
number of protons in many
elements by using
the wavelength of the X-ray
produced by a particular
metal anode of the X-ray tube.
The number of PROTONS determines
the identity of an element. A NUCLIDE is a particular kind of
atom containing a definite number of protons and neutrons.
Note Taking Guide: Episode 302
Nucleons- PARTICLES in the NUCLEUS of ATOM
• PROTONS
• NEUTRONS
Atomic Number- NUMBER of PROTONS in the
NUCLEUS of an ATOM
Neutral atom- # of PROTONS (+) = # of ELECTRONS(-)
Isotope- ATOMS of an ELEMENT that have DIFFERENT
NUMBERS of NEUTRONS.
Isotopes of Hydrogen
ISOTOPE
PROTONS
NEUTRONS ABUNDANCE SYMBOL
Hydrogen-1
PROTIUM
1
0
1
H
Hydrogen-2 1
DEUTERIUM
Hydrogen-3
TRITIUM
5 999/6000
1
1/6000
1
2
H
1
1
3
2
H
1
Mass Number- TOTAL number of PROTONS and NEUTRONS
in an ATOM
Example: Carbon-14 146C Neon-20 2010Ne
Particle Charge Mass Location
Location
Subatomic
Mass
Discovered
particle
Charge
by
proton
+
1 amu
Neutron(1932)
0
1amu
nucleus
CHADWICK
nucleus
Electron
1/1837
J.J.
cloud
amu
THOMSON
Atomic Mass- AVERAGE of the MASSES of all the element’s
ISOTOPES
Subatomic Particles
# of protons =ATOMIC NUMBER
# of electrons(in neutral atom) = ATOMIC NUMBER
# of neutrons = MASS NUMBER – ATOMIC NUMBER
electron
iron:
-
oxygen-17:
26
Fe
55.8
26 protons
26 electrons
30 neutrons
O
15.99
4
4
2 protons
He
2 electrons
2
2 neutrons
The Chemistry Quiz
CR1. C CR2. B 1. C
Nuclide
#
PROTON
8 protons
8 electrons
9 neutrons
8
2. B
#
NEUTRON
3. A
(A)
MASS
NUMBER
4. A
(Z)
ATOMIC
NUMBER
5. C
# e-
Carbon-14
Mass #
6
8
(14-6)
14
6
6
53Li
3
2 (5-3)
5
3
3
53Li2+
3
2 (5-3)
5
3
1
Atomic # - charge = e-
3 – 2 = 1 e-
AVE
RAG
E
ATO
MIC MASS
A MASS SPECTROMETER is an instrument used to
measure the masses and amounts of the nuclides of
elements.
The ATOMIC MASS is the average atomic mass of all the
nuclides of an element as they occur in NATURE.
To find the average atomic mass find the sum of the percent
times the mass of each nuclide and divide by 100.
Example: Neon-20 has a mass of 19.992 amu and neon22 has a mass of 21.991 amu. In a sample 90% is neon-20
and 10% is neon-22. Find the atomic mass of neon.
(90 % x mass of neon-20 ) + ( 10% x mass of neon22 )
(% x mass of neon-20)+(% x mass of neon-22) =
100
= (90 x 19.992 u)+(10 x 21.991 u) = 20.192 u
100
OR (0.90 x 19.992 u)+(0.10 x 21.991 u) = 20.192 u
http://www.colby.edu/chemistry/OChem/DEMOS/MassSpec.html
6% = .06
move two places to the left
10.% = .10
1% = .01
% x mass of each isotope)
RADIOACTIVITY
Note Taking Guide: Episode 1501
Nucleons:
.are particles occupying the NUCLEUS
.consist of + charged PROTONS and NEUTRAL NEUTRONS
.have almost 2000 times the MASS of ELECTRON
.are made up of QUARKS and LEPTONS
mass NUMBER(A)
PROTONS +
27
Al
NEUTRONS
13
atomic NUMBER(Z)
= # of PROTONS (= ELECTRONS if neutral)
Nuclear Notation:
27
13 Al has 13 protons and 14 neutrons, for a total of 27
nucleons.
28
13 Al has 13 protons and 15 neutrons, for a total of 28
nucleons.
isotopes: atoms of SAME element with different numbers of
NEUTRONS (different MASS)
Forces Acting on Nucleons:
Strong forces –
-forces of ATTRACTIONS between nucleons
-are independent of the CHARGE of the nucleon
-are short range (exist only
between CLOSEST neighbors)
Electrical force –
-force of REPULSION between
POSITIVE charged protons
-are long range
When are nuclei unstable?
a. large nuclei (Z > 82) electrical forces of REPULSION
are greater than strong forces
of ATTRACTION
b. wrong neutron : proton RATIO
http://www.pbs.org/wgbh/aso/tryit/atom/builder.html
A radioactive isotope:
- has an UNSTABLE nucleus
- spontaneously emits a PARTICLE and DECAYS into another
ELEMENT
Transmutation – changing into another ELEMENT through
radioactive DECAY
BECQUERL discovered radiation. MARIE AND PIERRE
CURIE discovered the radioactive elements Plutonium and
Radium.
Animation of deflection
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/radioa7.swf
Types of Radioactive Emission:
Alpha
Beta
Symbo Composition
l
Stopped
by
4
2He
0
-1 e
PAPER
METAL
FOIL
LEAD
Gamma 
2p+ 2n0
ELECTRON
ENERGY
Charge Mass
2+
-
4 amu
0
0
1/1837
amu
Electrical
Field
To To +
No
effect
Nuclear Equations:
alpha decay:
210
214
4
84Po  2He +
82Pb
beta decay:
0
209
209
82Pb  -1 e +
83Bi
During beta decay, a neutron
changes into a proton and an
ELECTRON.
0
1
1
0n 1p +
-1 e
half-life(t1/2):
• the TIME it takes for HALF the
SAMPLE of a radioactive sample to
DECAY
• ranges from a fraction of a SECOND to
billions of YEARS
• is NOT affected by EXTERNAL conditions
The Chemistry Quiz 1. B 2. D 3.A
4. D
http://www.wwnorton.com/college/chemistry/gilbert/tutorials/ch2.htm
http://lectureonline.cl.msu.edu/~mmp/applist/decay/decay.htm
nuclear decay animation % ½ life
http://www.darvill.clara.net/nucrad/hlife.htm
half-life
http://www.sciencecourseware.com/VirtualDating/files/RC0/RC_0.html
5. D
types of decay
carbon dating
NUCLEAR reactions involve a change in the atom’s nucleus.
RADIOACTIVITY is the spontaneous emission of energy rays
from unstable atomic nuclei. The rays and particles emitted by
the radioactive material are called RADIATION. In a nuclear
reaction some of their mass is changed into ENERGY
NUCLEAR STRUCTURE
Protons and neutrons are made up of three smaller particles
called QUARKS.
An ANTIPARTICLE is a mirror-image particle that exists for
every particle.
There are 6 kinds of quarks UP, DOWN, TOP, BOTTOM,
STRANGE & CHARMED. Each comes in three FLAVORS or
COLORS, RED, BLUE, or GREEN.
http://education.jlab.org/atomtour/
Jefferson labs atom tour
When an atom loses an alpha particle, the atomic number goes
down by 2 and the mass number goes down by 4.
http://chemmovies.unl.edu/ChemAnime/ALPHAD/ALPHAD.html
alpha decay equations
http://ie.lbl.gov/education/glossary/AnimatedDecays/AlphaDecay.html - alpha decay animation
Carbon-14 undergoes beta radiation.
0
14
14
The reaction is
6C 
7 N +
-1e
When an atom loses a beta particle the atomic number goes up
by 1 and the mass number does NOT CHANGE.
http://chemmovies.unl.edu/ChemAnime/BBETAD/BBETAD.html Beta decay equations
Gamma radiation does not affect the atomic # or mass #.
http://www.wwnorton.com/college/chemistry/gilbert/tutorials/ch2.htm
balancing nuclear reactions
Note Taking Guide - Program 1502
TYPES OF NUCLEAR REACTIONS
NATURAL transmutation - Uranium spontaneously decays.
238
234 Th
4
92U 
90 + 2He
ARTIFICIAL transmutation - bombardment of a stable isotope
to force it to decay.
14
4
1
+ 178O
7N + 2He  1 p
Nuclear bullet
When the bullets are + charged, they are REPELLED by the
nucleus they are bombarding. To overcome the repulsions, they
must be ACCELERATED to very high speeds by PARTICLE
accelerators.
nuclear fission - Heavy nuclei are bombarded with neutrons
and split.
1
235
142
+ 9136 Kr + 3(10n) + E
0n +
92U
56 Ba
Mass of particles produced is slightly LESS than the mass of
the reactants.
This mass is converted into ENERGY. (E = mc2)
Critical mass: MINIMUM mass of FISSIONABLE material
required for a CHAIN REACTION
nuclear reactors: control fission CHAIN reactions to produce
energy
dangers:
nuclear fusion - combination of SMALLER nuclei into ONE
with release of ENERGY
hydrogen fusion
http://www.wwnorton.com/college/chemistry/gilbert/tutorials/ch2.htm
3
+
1H
4
1

2 He + 0n + E
DEUTERIUM
TRITIUM
HELIUM
Mass of particles produced is
much LESS than the mass of
the REACTANTS.
This MASS is converted into
energy. (E = mc2)
2
1H
.