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Chapter 3 – Atoms: The
Building Blocks of Matter
Section 3-1 – The Atom: From
Philosophical Idea to Scientific
Theory
The first people to think about
particle theory were the
_____________ around
___________.
Greeks
400 BC
One in particular was
__________. The word atom in
Greek means _______.
Democritus
indivisible
Following Democritus was
_________. He didn’t believe in
atoms. He thought matter was
___________.
Aristotle
continuous
This idea succeeded for about
_______years. Neither view
was supported by __________
_________ until ________.
2000
experimental evidence
The 18th century
By the late ________, most people
thought of an _______ as
something that could not be broken
down and that could _________
with other elements to form
__________.
1800’s
combine
Atom
compounds
Scientists still weren’t sure,
however if they always
combined in the same
________.
proportions
In the late 1790’s scientists had
better _________ which allowed
them to study chemical
reactions ___________.
balances
quantitatively
This led to the law of
_______________________. It
essentially says that as long as
nothing enters or leaves a chemical
reaction, _______ remains
constant.
conservation of mass
mass
Antoine-Laurent de Lavoisier
• He was obsessed
with measuring mass
during chemical
reactions.
• He observed that
when chemical
reactions are carried
out in a closed
system, the mass of
the system is not
changed.
• He was obsessed
with the latest
equipment for
measuring mass.
• He spent a great deal
of the French
taxpayers money on
this equipment.
• He died in the French
Revolution.
It also lead to the law of
__________________ which
essentially says that regardless of
the _________ or _________ of
the sample, the elements that
make it up are always there in the
same ____________.
definite composition
size or source
proportions
Law of Definite Proportions
Joseph Louis Proust
(1754-1826)
Joseph Louis Proust observed that Copper carbonate (CuCO3) occurs in nature
as the mineral malachite (a), it forms as a patina on copper roofs (b) and bronze
statues, and can also be synthesized in the laboratory (c). Regardless of its
source, basic copper carbonate has the same composition.
Since the composition of copper carbonate is the identical regardless
of the source, Proust called this generalization as the law of definite
proportions.
Swedish chemist Berzelius
heated certain amount of lead
with various amount of sulfur. He
found that when he used 1.55 g of
sulfur (yellow) and 10.0 g of lead
(gray) he got 11.55 of lead sulfide
(black).
Jons Jacob von Berzelius
1779-1848
If sulfur were taken in excess of 1.55g, Berzelius found that the excess
amount of sulfur did not react. Similarly if had 1.55 g of sulfur and added
lead in excess of 10.0 g, he found that the excess lead did not react
The law of definite proportions – Berzelius View
Definite proportions – A Closer Look
The law of definite proportions. Berzelius' experiment with lead and sulfur
are interpreted in terms of Dalton's atomic theory.
The electrolysis of water
Henry Cavendish (1731 - 1810) further
illustrated the law of definite proportion
by electrolyzing water.
Electrolysis of water. During electrolysis,
water decomposes to give hydrogen gas
and oxygen gas always in a 2-to-1 volume
ratio when energy is supplied by a battery
or other source of direct current (dc).
http://wps.prenhall.com/wps/media/objects/439/449969/Media_Portfolio/Chapter_04/Electrolysis_of_Water.MOV
More complicated is the law of
______________. It says that if ______ or
more different _______ are made of the
same 2 elements, the ratio of the ________
element combined with a fixed mass of the
1st element is always a ________ of small
___________ numbers
multiple proportions
2nd
whole
two
ratio
An example of this would be the
compounds of ___________
and ___________.
carbon dioxide
carbon monoxide
John Dalton’s Atomic Theory of Multiple Proportions
Dalton theory multiple proportions:
Elements can combine with each other
in more than one set of proportions.
For example, hydrogen and oxygen
combine with each other in two different
proportions and form two entirely
different compounds.
2 H 2  O 2  2H 2 O
Water
John Dalton
(1766-1848)
2H 2  2O 2  2H 2O 2
Hydrogen peroxide
Although these two
molecules contain only
hydrogen and oxygen,
they are not the same
compound.
These three laws prompted
John Dalton to propose his
atomic theory. It basically says:
1. All matter is made of
______________
______________ called
____________
indivisible
indestructible
atoms
2. Atoms of the same
___________ are chemically
and physically the ________.
element
same
3. Atoms of ___________
elements are chemically and
physically the ________.
different
different
4. When atoms _______ in a
chemical reaction, they do so in
___________, ____________
number ratios.
combine
small
whole
In a chemical reaction, atoms
aren’t ____________ or
____________, they are simply
_____________.
created
destroyed
rearranged
Section 3-2 – The Structure of
the Atom
Atoms consist of
___________________ regions.
One of them contains the
___________________ and
___________________. It is
called the ___________________.
2
protons
neutrons
nucleus
The other area surrounds the
nucleus. It contains
___________________
particles called
___________________.
negatively charged
electrons
Actually
___________________,
___________________, and
___________________ are all
___________________.
protons
electrons
neutrons
subatomic particles
The electron was discovered by
working with a tube that
contained a
___________________ at very
low pressure.
gas
When ___________________
passed through it, it would light
up. It is called a
_________________________
____________.
an electrical current
cathode ray tube
The fact that the ray was
deflected by a negative charged
showed that the ray had a
___________________ charge.
negative
The fact that the ray could move
a paddle wheel demonstrated
the ___________________
nature of the ray.
particle
The ray was actually made of
___________________.
electrons
The scientist credited with
naming the
___________________ was
___________________.
electron
JJ Thomson
It stands to reason that where
there is a negative charge, there
must be a
___________________ charge
to balance it.
positive
_________________________
and associates tried to bombard
___________________ with
___________________.
Ernest Rutherford
gold
alpha particles
They expected that most of the
α particles would
________________________.
go straight thru (92%)
For the most part, this was true, but
some were ___________________
and a very small percentage were
actually _____________________.
deflected (6%)
shot straight back (2%)
It took 2 years, but Rutherford
developed a 2 part explanation. It
was:
• Atoms are mostly empty space
• Atoms must have a densely packed
positively charged nucleus.
To summarize the
___________________,
___________________ are the
lightest and can be found
______________________. They
have a ________________ charge.
subatomic particles
electrons
orbiting the nucleus
negative
___________________ and
___________________ are the
heaviest and are found in the
___________________.
Protons
neutrons
nucleus
___________________ have a
positive charge and
___________________ have
___________________ charge.
Protons
neutrons
no
Section 3-3 – Counting Atoms
neutral, atomic number,
chlorine, proton, 17, electron
A neutral atom of chlorine would have 17
protons and 17 electrons if it is neutral.
Because chlorine has an atomic number of
17, it would have 17 protons and
assuming it is neutral, it would have 17
electrons.
isotope, tritium, deuterium, protium,
atomic mass, 1, 2, 3, hydrogen
The three isotopes of hydrogen are protium
with an atomic mass of 1, deuterium with
an atomic mass of 2, and tritium with an
atomic mass of 3.
Hydrogen has 3 different isotopes. They are
protium, deuterium, and tritium with atomic
masses of 1, 2, and 3 respectively.
nuclide, superscript, subscript,
hyphen notation, uranium, nuclear
symbol
You can indicate nuclides 2 different ways;
Hyphen notation means you write the
symbol with a dash and the atomic mass
or you could use the nuclear symbol
method where you write the symbol and
put the atomic mass as a subscript to the
upper left and the atomic number as a
subscript to the lower left.
Example
• U-238
238
92
U
carbon-12, atomic mass unit
An atomic mass unit is defined as one
twelfth of a carbon-12 atom.
average atomic mass, isotopes,
percentage, naturally occurring
The average atomic mass of an element
takes into account the percentages of the
naturally occurring isotopes.
Average atomic mass can be calculated by
multiplying the atomic masses of the
isotopes by their naturally occurring
percentage in a mixture.
mole, carbon-12, Avogadro’s
number, molar mass
A mole is defined as 12 g of the carbon-12
isotope. It has Avogadro’s number of
atoms. The molar mass of all other
elements is compared to a mole of carbon12.
Subatomic Particles
The atoms of all elements consists of positively charged protons,
neutral neutrons and negatively charged electrons. The protons
and the neutrons together are called as nucleons and they are
located at the nucleus of the atoms.
The Atomic Number
The number of protons in the nucleus of an atom determines the
atomic number (Z) and indicates the element's identity. For a
neutral atom, the atomic number also describes the number of
electrons around the nucleus.
Atomic Mass and Atomic Number
Mass number A (sum of protons and neutrons)
 Atomic number Z (number of protons)
= number of neutrons.
Isotopes of hydrogen
While the number of protons in the nucleus defines an element's
identity, variations on the number of neutrons in the nucleus give rise
to different isotopes of the same element.
Mass Numbers and Atomic Numbers
The atomic number is equal to the number of protons in an atom
of that element. The mass number is the sum of the number of
protons and neutrons.