Download Modern Atomic Theory - Whitmore Lake Public Schools

Chapter #3
Chapter #3
ATOMS:
The Building
Blocks of
Matter
• Atoms: The Building Blocks of
Matter
3-1 Early Atomic Theory
Do Not
need in
notes
• Atoms are so small they cannot be observed directly. Scientists could
use only experimental data to help describe the atom.
• Around 400 B.C., Democritus (a Greek philosopher) suggested that the
world was made of two things - empty space and tiny particles called
atoms.
• During the 1800's, a French Chemist (Antoine Lavoisier) discovered
that chemical "changes" occurring in a closed system - the mass after
a chemical change equaled the mass before the chemical change.
• He proposed that, in ordinary chemical reactions, matter can be
changed in many ways, but it cannot be created or destroyed (Law of
Conservation of Mass).
• Work by another French Chemist, Joseph Proust, had observed that
specific substances always contain elements in the same ratio by mass
(Law of Definite Proportions.)
Foundations of Atomic Theory
• Law of Definite Proportions: The
elements composing a compound are always
found in the same ratio by mass.
• Law of Multiple Proportions: The masses
of one element that combine with a fixed
amount of another element to form more
than one compound are in the ratio of
small whole numbers. Example CO, CO2
For example: Oxygen can combine with Carbon to form
Carbon Monoxide, CO, or form Carbon Dioxide, CO2.
Compound
Mass of C
in Sample
Mass of O in
Sample
Ratio of O masses combined
with constant mass
Carbon Monoxide, CO
12 g
12g
16 g
32 g
1:1
2:1
Carbon Dioxide, CO2
• Dalton was the founder of Atomic Theory.
Dalton’s Atomic Theory
1.
2.
3.
4.
5.
All matter is composed of extremely small particles
called atoms.
Atoms of a given element are identical in size, mass
and other properties; atoms of different elements
differ in size, mass, and other properties.
Atoms cannot be subdivided, created, or destroyed.
Atoms of different elements combine in simple
whole-number ratios to form chemical compounds.
In chemical reactions, atoms are combined,
separated, or rearranged.
Modern Atomic Theory
• Element have a characteristic average mass
which is unique to that element.
• Atoms cannot be subdivided, created, or
destroyed in ordinary chemical reactions.
However, these changes CAN occur in nuclear
reactions!
• All matter is composed of atoms
• Atoms of any one element differ in properties
from atoms of another element
Section 3-2
• Atom- the smallest particle of an
element that retains the chemical
properties of that element.
• Nucleus- is the positively charges,
dense central portion of the atom
that contains nearly all of its mass
but takes up only an insignificant
fraction of its volume.
Subatomic Particles
Electrons e-
Negatively charged particles found
around the nucleus in shells, energy
level or electron clouds
Protons
Positively charged particles. Found
in the nucleus
p+
Neutrons N
No charge. Found in the nucleus.
The Atomic Scale
• Most of the mass of the atom is in
the nucleus (protons and neutrons)
• Electrons are found outside of the
nucleus (the electron cloud).
e- have very tiny mass.
• Most of the volume of the atom is
empty space
Drawing atoms
•
1.
2.
3.
•
In the nucleus
Symbol
# of p+
# of N
Outside the nucleus in the energy
shells/level
1. electrons
Famous Scientist
Scientist
Experiment
Name
What it proved
JJ Thomson
Cathode Ray
Electrons have a
negative chare
Robert Millikan
Oil Drop
Mass of an
electron
Ernest Rutherford Metal Foil or gold
foil
Nucleus contains
positive charge
Discovery of the Electron
Do NOT need
in Notes
• In 1897, J.J. Thomson used a cathode ray
tube to deduce the presence of a negatively
charged particle.
• Cathode ray tubes pass electricity through a
gas that is contained at a very low pressure.
• Thomson was awarded the
Nobel Prize in 1906 for his
"discovery" of the first subatomic particle; the electron.
This discovery strongly
implied that Dalton was wrong
and that the atom was not
the smallest particle of
matter. It looked as if the
atom could be broken down
into even smaller pieces, and
to Thomson these smaller
pieces were his negatively
charged electrons.
Do NOT need
in NOTES
Conclusions from the
Study of the Electron
•
Do NOT need in
NOTES
Cathode rays have identical properties
regardless of the element used to
produce them. All elements must contain
identically charged electrons.
• Atoms are neutral, so there must be
positive particles in the atom to balance
the negative charge of the electrons
• Electrons have so little mass that
atoms must contain other particles that
account for most of the mass
Thomson’s Atomic Model
Do NOT need
in NOTES
• Thomson believed that the electrons
were like plums embedded in a positively
charged “pudding,” thus it was called
the “plum pudding” model.
Rutherford’s Gold Foil
Experiment
•
•
Do NOT need in
NOTES
Alpha particles are helium nuclei
Particles were fired at a thin sheet of gold
foil
• Particle hits on the detecting screen (film) are
recorded
Rutherford’s Findings
• Most of the particles
passed right through
• A few particles were
deflected
• VERY FEW were greatly
deflected
• Conclusions:
• The nucleus is small
• The nucleus is dense
• The nucleus is positively
charged
DO NOT Need
in Notes
Section 3-3
• Atomic number (Z)
of an element is the
number of protons in
the nucleus of each
atom of that
element.
• The number of
protons = the
number of electrons
6
C
Carbon
12.011
• Mass Number
• Mass number is the number of
protons and neutrons in the nucleus
of an isotope.
• Mass # = p+ + n
• SOooo the number of Neutrons =
• n= Mass # - p+
Isotopes
Mass #
Atomic #
Symbol
• Isotopes are atoms
of the same
element that have
different masses.
(number of
neutrons)
Nuclear Symbols
Mass number
number
Mass
(p+ +(p+n)+ n)
Atomic number
(# of p+)
235
Element
symbol
92
235
92
U
Hyphen Notation
Sodium-23
(23 is the mass #)
Sooo… 23- 11 (atomic #) = 12 for the
# of neutrons.
11 is the # of protons and electrons.
Isotopes of H
Isotopes
p+ e-
n
Hydrogen–1
(protium)
1
1
0
Hydrogen-2
(deuterium)
1
1
1
Hydrogen-3
(tritium)
1
1
2
The Mole
•
•
•
•
1
1
1
1
dozen =12
gross = 144
ream = 500
mole = 6.022 x 1023
• There are exactly 12 grams
of carbon-12 in one mole
of carbon-12.
Calculations:
Converting moles to grams
• Given # of mole X ? g
(look at periodic table)
1 mole
=
g of
• How many grams of lithium are in 3.50 moles
of lithium?
• 3.50 mole X 6.941 g = 24.29 g Li
1 mol
Calculations:
Converting grams to moles
• Given # of g X 1 mol =
mol of
g (look at periodic table)
• How many moles of lithium are in
18.2 grams of lithium?
• 18.2 g X 1 mol Li = 2.622 mol Li
6.941 g
Avogadro’s Number
• Is the number of particles in exactly one
mole of a pure substance.
• 6.022 x 1023 is called “Avogadro’s Number”
in honor of the Italian chemist Amadeo
Avogadro (1776-1855).
I didn’t discover it. Its just
named after me!
Calculations:
Converting Moles to Particles
• Given # of mol x 6.022 x 1023 part=
atoms
1 mol
• How many atoms/particles/molecules of
lithium are in 3.50 moles of lithium?
• 3.50 mole X 6.022 x 1023 = 2.11 x 1024 atoms of Li
1 mol
Calculations:
Converting Particles to Moles
• Given # of particles x 1 mole =
mol
6.022 x 1023
• How many moles of lithium are there
in 1.2044 x 1024 particles of Li?
• 1.2044 x 1024 part x 1 mole
= 2.0 mol Li
6.022 x 1023 part
Calculations:
Converting grams to particles
• Given # of grams x 1 mol x 6.022 x 1023=
?g
particles
1 mol
• How many atoms/particles/molecules of
lithium are in 18.2 g of lithium?
• 18.2 g x 1 mol x 6.022 x 1023 = 1.58 x 1024 particle Li
6.941g
1 mol
Calculations:
Converting particles to grams
• Given # of particles x 1 mol
x
?g=
6.022 x 1023 1 mol
• How many grams are there in 8.02 x 1025
particles of lithium?
g
Work Cited
•
•
•
•
“JJ Thomson”. Photo. July 28, 2006.
http://www.sciencemuseum.org.uk/online/electron/section2/recor
ding.asp
Cathode Ray Image and JJ Thomson Model. Image. July 28, 2006.
http://www.brooklyn.cuny.edu/bc/ahp/LAD/C3/C3_Electrons.html
“Gold Foil Experiment”. Image. July 28, 2006. http://www.avonchemistry.com/atom_lecture.html
“Rutherford”. Photo. July 28,2006.
http://www.anthroposophie.net/bibliothek/nawi/physik/rutherfor
d/bib_rutherford.htm
• “Mole”. Photo. Aug 8, 2006.
http://www.mwt.net/~bionorse/chemistry.htm
•
•
•
•
•
“Hydrogen Isotopes”. Picture. August 4, 2006.
www.sr.bham.ac.uk/xmm/atom.html
“Amedeo Avogadro”. avagadroc.jpg August 4, 2006.
poohbah.cem.msu.edu/Portraits/PortraitsH...
“Uranium symbol”. Picture. August 4, 2006. www.webelements.com/
webelements/scholar/...
Holt, Rinehart and Winston. Modern Chemistry. Harcourt Brace &
Company. 1999.
“Atom Comic Cover”. Photo. Aug. 12, 2006.
http://home.cfl.rr.com/fradford/Ato
m/Atom20.jpg