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Atoms, Molecules and Ions

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Check your prior knowledge…
1. Describe what atoms are made of…
2. Estimate the size of atoms.
1. Draw a picture of a simple atom on a sheet
of paper.
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2
Observations!
Observations like these led early philosophers to
wonder about the fundamental nature of matter…
Is it continuous and infinitely divisible?
Or is it divisible only until a basic, invisible particle
that cannot be divided any further is reached?!
3
Atoms:
The Building Blocks of Nature
ἄτομος
Chapter 3
400 BC Greece
Democritus names the basic particle of
nature an atom.
5
He proposed that if matter were repeatedly
divided, the eventual result would be an atom, an
indivisible, “uncuttable” basic unit of matter.
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But it couldn’t be tested.
Democritus couldn’t prove it. It was 400 BC
for crying out loud!
And there was the problem of ARISTOTLE.
Aristotle disagreed and NOBODY crossed
Aristotle. He was too powerful back then…
And stayed that way for almost 2000 years.
7
18th Century… that’s when it all
started to come together…
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The concept of the atom was resurrected!
The late 1700’s
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Lab circa 1800
10
th
18
Century thinking…
Chemists accepted that an element couldn’t be broken
down by ordinary chemical means.
They assumed that these elements combined to form
compounds…
They just couldn’t figure out exactly how the different
substances could combine with one another to form
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new ones…
The foundation of modern chemistry dates to
this time when scientists finally began to give
rules to how matter interacts.
How did it happen?!
<I hear you all gasp in amazement!>
Well, I’ll tell you.
There was a shift.
Remember… up until this time the whole basic
particle of nature was speculation.
<what does that mean?>
There were equipment improvements, like balances,
so mass was more accurately
This led to more accurate studies of compounds.
This led to the discovery of several basic laws.
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Three basic laws…
• Law of Conservation of Mass (Lavoisier)
• Law of Definite Proportions (Proust)
• Law of Multiple Proportions (Berthollet)
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Law of Conservation of Mass
Mass isn’t created or destroyed during
ordinary chemical reactions or physical
changes.
Carbon + Oxygen = CO
Mass x
Mass y
Mass x + Mass y
15
16 X
+
8Y
Law of Conservation of Mass
8 X2Y
And the reverse holds true…
CO =
(Mass x + Mass y)
Carbon + Oxygen
Mass x
Mass y
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Law of Definite Proportions
A compound contains the same elements in
exactly the same proportions by mass - no
matter how much or how little there is of it.
18
And in simpler language:
Every chemical compound has one and only
one chemical formula.
No matter what process you use to make
water, the formula will always be H2O.
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Basically
The Law of Definite Proportions states that no
matter how you make a chemical compound,
it's got the same ratio of elements.
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An example: Whether you make H2O by
combining H + O or by decomposing H2O2
(hydrogen peroxide),
the resulting H2O will still be 2 atoms of
hydrogen and 1 atom of oxygen.
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Sodium chloride - NaCl
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• NaCl has a fixed proportion of elements.
• It is always 39.43% by mass Sodium and
60.66% by mass Chlorine.
The exact same proportions of Na and Cl must
always be combined in order for salt to be
created.
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Law of Multiple Proportions
If two or more different compounds are
composed of the same two elements, then the
ratio of the masses of the second element
combined with a certain mass of the first
element is always a ratio of small whole
numbers.
24
Basically…
• The same two elements can combine in
multiple ways to create different
compounds.
• Any time two elements can form more than
one compound with each other, a particular
ratio of small whole numbers between the
masses takes place.
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Remember… this is the
th
18
century
What seems obvious to us was pretty
revolutionary back in Dalton’s day. They
were trying to figure out how things combined
to make compounds and how to explain the
process. They were trying to make sense of
what they observed, but didn’t have the
technology to sort it out. Kudos to them, hey!
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Think about it like this:
Definite Proportions means no matter how you make a
compound – it’s always the same ratio of elements.
Multiple Proportions has to do with the different
compounds you get when you combine the
. The ratios of those elements in the first
compound will be some whole number multiple of the
other compounds.
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Find a buddy!
Take 3.5 minutes to discuss
these 3 laws…
Explain it and
make sure you’ve got it!
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And back to our story…
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John Dalton was a schoolteacher
in England, and in 1808 he
proposed an explanation that
pulled together all these laws.
It was ground-breaking.
Still is!
He reasoned that…
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Dalton’s Atomic Theory (1803)
1. Elements are composed of extremely small particles
called atoms.
2. All atoms of a given element are identical, having the
same size, mass and chemical properties. The atoms
of one element are different from the atoms of all
other elements.
3. Atoms cannot be subdivided, created, or destroyed.
4. Compounds are composed of atoms of more than
one element. In any compound, the ratio of the
numbers of atoms of any two of the elements present
is a small whole number ratio.
5. A chemical reaction involves only the separation,
combination, or rearrangement of atoms; it does not
result in their creation or destruction.
1. All matter is made of indestructible atoms. This means that
atoms are as small as matter gets, like tiny unbreakable
billiard balls.
2. All atoms of an element have identical chemical and physical
properties. This means that if you know the properties of one
atom of an element you can predict what the properties of all
atoms of that element are.
3. Atoms of different elements have different chemical and
physical properties. This means that the properties of each
element define that element and no two elements can be
identical in how they behave.
4. Atoms of different elements always combine in whole-number
ratios when they form chemical compounds. This means that
all chemical formulas have the general form AxBy, where x
and y are whole numbers. This is, in effect, the same thing
as the Law of Multiple Proportions.
5. Atoms are never created or destroyed during chemical
32
reactions. This is the same thing as the Law of Conservation
1. Everything is made of atoms like small billiard balls.)
2. All atoms of the same element are identical in every way.
(Except the bit about mass. Isotopes keep these atoms from
being identical.) All atoms of different elements are
different.
3. Atoms are can’t be broken. They can’t be subdivided,
created or destroyed. (Except now we have subatomic
particles & physicists use particle accelerators to break
atoms into quarks, leptons, bosons and magical fairies.)
4. Atoms of different elements combine in whole number
ratios. You can have H2O or H2O2, but you can’t have
H2.2O
5. In chemical reactions, atoms are rearranged.
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And with that, the world of chemistry
was forever changed.
Well, it was changed until less than a hundred
years later, when it got all crazy again with
Thomson and Rutherford and Bohr and stuff.
But we’ll talk about that later.
34
Dalton turned Democritus’ idea into a
scientific theory that could be tested by
experiment. This is GOOD!
But since it is testable…
guess what happened?
Technology happened…and more discoveries
happened.
Let’s look at what we know now.
35
Dalton’s Atomic Theory (1803)
1. Elements are composed of extremely small particles
called atoms.
2. All atoms of a given element are identical, having the
same size, mass and chemical properties. The atoms
of one element are different from the atoms of all
other elements.
3. Atoms cannot be subdivided, created, or destroyed.
4. Compounds are composed of atoms of more than
one element. In any compound, the ratio of the
numbers of atoms of any two of the elements present
is either an integer or a simple fraction.
5. A chemical reaction involves only the separation,
combination, or rearrangement of atoms; it does not
result in their creation or destruction.
Today we know that atoms are
divisible into even smaller particles
(protons, neutrons, electrons…
quarks…leptons…)
We also know that a given element
can have atoms with different
masses. (called isotopes)
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Atomic theory hasn’t been
discarded – only modified!
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These concepts remain unchanged:
1) All matter (elements) is composed of atoms.
2) Atoms of any one element differ in properties
from atoms of another element.
3) A chemical reaction involves separation,
combination or rearrangement of atoms that are
not created or destroyed.
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Let’s Review Dalton’s Atomic Theory!
I’ll give you and a partner one of the 5 postulates.
You write down the # and describe that postulate.
You can think of a creative way to describe it – use a
sketch or formula or diagram.
(I’ll give you a piece of paper.)
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Let’s review and share ideas!
In the lab, find someone with a different #
postulate.
Tell them your number and describe your
postulate. Listen and they will describe theirs.
Find a new person with a different number until
you’ve found all 5 postulates.
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Can we see atoms?!
. . . kind of . . .
Remember, atoms are so small they can only be
“seen” with a special scanning microscope.
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Here are approximate diameters.
•
•
•
•
atom = 1 x 10-7 mm
nucleus = 1 x 10-12 to 1 x 10 -11 mm
neutron or proton = 1 x 10-12 mm
electron - not known exactly, but thought to
be on the order of 1 x 10-15 mm
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100 000 000 atoms of Cu = 1 cm
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What is this number written in scientific notation?
Atomic force microscopy (AFM)
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X-ray diffraction is another way to “see” atoms.
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IBM: A Boy and His Atom
With the use of a scanning tunneling
microscope, IBM made a movie so small it
can be seen only when you magnify it 100
million times. A movie made with atoms.
https://youtu.be/oSCX78-8-q0
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In a nutshell
• Law of Conservation of Mass: The amount
of stuff you form in a reaction is equal to
the amount of stuff you started with.
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The Law of Definite Proportions
Every chemical compound has one and only
one chemical formula. For example, no
matter what process you use to make water,
the formula will always be H2O.
49
Law of Multiple Proportions
The same two elements can combine in multiple ways
to create different compounds that have the same
whole number ratio masses as the original elements:
• H2O and H2O2
• NO and NO2
• CO and CO2
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H2O and H2O2
• In the first compound, the amount of O
needed to combine with 2 g of H is 16 g.
• In the second compound, the amount of O
needed to combine with 2 g of H is 32
grams.
• The ratio of 32:16 works out to a 2:1 ratio,
it follows this law.
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Target Qs:
1.Characterize the size of an atom.
2.How did the approach to the concept of “atoms”
differ between Democritus and Dalton?
H2SO4 - Sulfuric Acid
• Sulfuric acid is made up of the individual
elements of H, S, and O.
• The chemical compound is written H2SO4.
• The same proportions of H, S, and O must
be combined to create sulfuric acid.
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Or in other words…
1) Everything is made of atoms. (TRUE)
2) All atoms of an element are identical in
every way (Not true due to isotopes)
3) Atoms of different elements are different
(true)
4) Atoms can’t be broken (true for chemical
reactions, but not for nuclear ones)
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Atoms combine in whole number ratios to
form compounds (i.e., you can’t have half an
atom in a compound) This is true…
5) In chemical reactions, atoms are
rearranged. (true)
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• Not all aspects of Dalton’s atomic theory
have proven to be correct.
1)Atoms ARE divisible into smaller particles
called subatomic particle: protons, electrons
& neutrons.
2)A given element can have atoms with
different masses (isotopes).
57
Bellwork #4 – 10/15
1. A chemical compound contains the same
elements in exactly the same proportions by
mass. Ibuprofen = C13H18O2.
2. H and O combine to form H2O. They also
combine to form H2O2.
3. The amount of stuff you form in a reaction
is equal to the stuff you started with.
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Bellwork #5: 10/17 and check
1) Give 3 main concepts in Dalton’s
atomic theory.
2) 180.18 g of glucose, C6H12O6,
always contains 72.06 g C, 12.12 g H
and 96.00 g O. What % of each of these
elements is present in glucose?
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• 1.
CaO + CO2
CaCO3
where the mass of the reactants = mass of
the products
•
• 2. N + O can form NO.
•
They can also form NO2.
•
•
H + O can form H2O.
•
They can also form H2O2.
•
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3. To make table salt, 1 atom of Na will combine
with 1 atom of Cl. Always.
To make water, 2 atoms of H will combine with 1
atom of O. Always.
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Bellwork #1
1. Law of Definite Proportions, any 2
samples of KCl have the same ratio of
elements.
2. Law of Conservation of Mass: When Na,
H and O form a compound, the mass of the
compound is equal to the sum of the
masses of the individual elements.
3. The ratio of O to C when 32 g of O
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combine with 12 g of O = 2:1
Dalton’s Atomic Theory (1808)
Law of Multiple Proportions
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