Download Atoms contain 3 particles

History of the Atom
In Atomic Theory, if we were to
zoom in on a copper wire, it might
look like the picture below.
What is between the atoms?
What did be believe before we
thought there were atoms?
We thought matter was continuous, not made of little particles
What would it have looked like?
Why would we have believed
matter was continuous?
Because it looks like it. Why don’t
you see atoms when you look at a
piece of copper wire?
Because atoms are sooooooo small.
How big is an atom?
If a baseball was blown up to the size of the
earth. An atom would be about the size of a
baseball.
Picture yourself out in space trying to see
someone holding a baseball in your backyard.
We could never hope to see an atom with visible light
Atom
We can “see” them with special microscope
called a scanning tunneling electron microscope.
Guess who the first to do this was?
Atoms were first proposed by 2,400 years ago
by the Greek philosopher
Democritus
BUT the idea did not catch on until 2,200
years later. Why did no one believe him?
Philosopher did not experiment, they just
thought. NO PROOF.
If we can’t see atoms
why do we believe in them now?
(even well before the SEM)
John Dalton (1766-1844)
• English School teacher and early
meteorologist
• Trying to learn what caused rain and
where it came from
• Discovered that the water actually came
out of the air itself
• Combined the concept of atoms with that
of elements
• His conclusion came from several
experiments. (not just guessing)
How could water be in air? If matter is
continuous, then there is no room in air for
water.
Air
Water
Air &
water
mixed??
How can two things occupy the same space??
Atomic theory of matter
Air
Water
Air & water mixed
The molecules of air and water can mix
because they do not occupy the same space
Experiments also showed that:
A given compound (say NaCl) had
the same % of elements, no matter
where he located it from. (ocean
water or made from Na & Cl)
Always
1 Na
& 1 Cl
by mass
39% Na & 61% Cl
Formation of NaCl from its elements
http://www.youtube.com/watch?v=2mzDwgyk6QM
Why should a compound have an exact % of elements
According the the continuous theory of matter I can mix
any amount of Na and Cl
Na
Na
Cl
NaCl
Cl
NaCl
atomic theory of matter: atoms of Na
react with atoms of Chlorine to form a
compound
Cl
Na + Na
Cl
+
+
Cl
Na
Can part of a Na atom react?
Na
Cl
Na
Law of definite composition: a sample of a
given compound will have the same
composition of elements no matter where it
was obtained. The composition is often
expressed as % mass.
Acetic acid (active ingredient in vinegar) C2H3O2
Can be made by fermenting fruit or by chemical reactions
with Crude Oil. Both are used as food ingredients. Same
compound 2C : 3H : 2O
By mass this is 49% C : 1% H : 50% O
• The law of definite composition: A
compound has the same composition whether
you find it here or on the other side of the
world, whether you find it in nature or if you
synthesize the compound.
Composition
of iron sulfide
Law of Multiple Proportions
CO2
CO
A law proposed by Dalton which states
that when elements combine, they do so
in the ratio of small whole numbers. For
example carbon and oxygen react to
form CO or CO2, but not CO1.8
Law of multiple proportion: when the same
elements combine to form different
compounds they do so in whole number
ratios.
Compounds with Hydrogen and Oxygen
Mass H (g)
Compound A
Compound B
.125 g
.250 g
Mass O (g)
1.00 g
1.00 g
What do you notice about this???
Why should there be whole numbers
involved?
Because of atoms!!!
Compound A
Compound B
O
O
H
H
H2O
2H:1O
O
H
H
H2O2
1H:1O
There is EXACTLY twice as much Oxygen in compound B
Law of Conservation of Mass
Massreactants = massproducts
If chemical reactions are rearrangements of
atoms, then mass would be conserved:
If atoms are rearranged, and not created or
destroyed, then the mass of the reactants must
equal the mass of the products.
Reactants
Products
Atoms are conserved.
• In natural processes,
atoms are not
destroyed; they are
recycled.
online
Dalton’s Atomic Theory
1.) All matter is made of tiny indivisible
particles called atoms.
2.) Atoms of the same element are
identical, atoms of different elements are
different.
3.) Atoms of different elements combine in
whole number ratios to form compounds.
4.) Chemical reactions occur when atoms
are separated, joined or rearranged
Is Dalton right on everything?????
Chemical reactions occur when atoms are
separated
joined
rearranged
+
+
• Bill Nye Atomic Theory
Subatomic Parts
Parts of Atoms
• J. J. Thompson - English physicist.
1897
• Made a piece of equipment called
a cathode ray tube.
• It is a vacuum tube - all the air has
been pumped out.
Thomson’s Experiment
Voltage source
-
+
Vacuum tube
Metal Disks
Thomson’s Experiment
Voltage source
-
+
Thomson’s Experiment
Voltage source
-
+
Thomson’s Experiment
Voltage source
-
+
Thomson’s Experiment
Voltage source
-

+
Passing an electric current makes a beam
appear to move from the negative to the
positive end
Thomson’s Experiment
Voltage source
-

+
Passing an electric current makes a beam
appear to move from the negative to the
positive end
Thomson’s Experiment
Voltage source
-

+
Passing an electric current makes a beam
appear to move from the negative to the
positive end
Thomson’s Experiment
Voltage source
-

+
Passing an electric current makes a beam
appear to move from the negative to the
positive end
Thomson’s Experiment
Voltage source
• By adding an electric field
Thomson’s Experiment
Voltage source
+

By adding an electric field
Thomson’s Experiment
Voltage source
+

By adding an electric field
Thomson’s Experiment
Voltage source
+

By adding an electric field
Thomson’s Experiment
Voltage source
+

By adding an electric field
Thomson’s Experiment
Voltage source
+

By adding an electric field he found the beam
was negative and that it was not just light. (light
is not affected by a magnet or electric field)
Thomson’s Experiment
Voltage source
+

By adding an electric field he found the beam
was negative and that it was not just light. (light
is not affected by a magnet or electric field)
Thomson’s Experiment
Voltage source
+

By adding a paddlewheel
Thomson’s Experiment
Voltage source
+

He added a paddlewheel
Thomson’s Experiment
Voltage source
+

He added a paddlewheel and saw that the
beam turned it.
Thomson’s Experiment
Voltage source
+

He added a paddlewheel and saw that the
beam turned it.
Thomson’s Experiment
Voltage source
+

He added a paddlewheel and saw that the
beam turned it.
Thomson’s Experiment
Voltage source
+

He added a paddlewheel and saw that the
beam turned it.
Thomson’s Experiment
Voltage source
+

Since the beam turned the paddlewheel, He
concluded that:
the beam had mass and was likely
composed of particles.
Experiments were repeated with many
different gases and all found the same
resulting beam of negative particles.
The conclusion was that all atoms have
these negative particles in them.
It was later called the electron, but at
the time Thomson called them
"corpuscles”.
By using the cathode ray tube and an electric
field. The deflection of the electron beam gave
the charge to mass ratio of a electron.
Voltage source
+
-
Charge of an electron?
1.7588028 1011 coulombs/kg
=
mass of an electron?
If one of the missing numbers could be found then
both would be known
Robert Millikan in 1909 set out to find the
charge on 1 electron, in one of the most clever
experiments to date.
Education
Millikan received a Bachelor's degree in
the classics from Oberlin College in 1891
and his doctorate in physics from Columbia
University in 1895 – he was the first to earn
a Ph.D. from that department.
– "At the close of my sophomore year
[...] my Greek professor [...] asked
me to teach the course in elementary
physics in the preparatory
department during the next year. To
my reply that I did not know any
physics at all, his answer was,
'Anyone who can do well in my
Greek can teach physics.' 'All right,'
said I, 'you will have to take the
consequences, but I will try and see
what I can do with it.'
Millikan Oil Drop movie
http://chemistry.umeche.maine.edu/~amar/fall2007/Millikan.html
.2
e-
.4
.3
e-
ee-
ee-
e-
e-
e-
He looked at the charges on the oil drops and
found that they were different by whole
numbers.
The smallest amount the charge changed was
the charge of 1 electron
He found that an electron has a mass of:
9.11 x 10-28 g
how “heavy” is that?
.0000000000000000000000000000911 g
If all atoms have these negative particles
in them, why isn’t everything electrically
charged?
Why don’t I get shocked when I touch
everything??
Atoms have a neutral charge because of…
Protons
So atoms have negative particles called electrons
and some positive stuff
(we don’t know about protons yet
in 1909)
How does this fit together to make an atom?
The first accepted idea came from J.J. Thomson
It was referred to as the
Plum Pudding Model
electrons
Positive charge smear
But then new evidence came to light
courtesy of
Lord Ernest Rutherford
Rutherford’s experiment
• Ernest Rutherford -English physicist.
(1910)
• Believed in the plum pudding model of
the atom
• Wanted to see how big they are.
• Used radioactivity.
• Alpha particles - positively charged
pieces- helium atoms minus electrons
• Shot them at gold foil which can be made
a few atoms thick.
Rutherford’s experiment
• When an alpha particle hits a
fluorescent screen, it glows.
• Here’s what it looked like
Lead
block
Uranium
Fluorescent
Screen
Gold Foil
He Expected
• The alpha particles to pass through
without changing direction very
much.
• Because…?
• …the positive charges were
thought to be spread out evenly.
Alone they were not enough to stop
the alpha particles.
What he expected
Because
He thought the mass was evenly
distributed in the atom
Since he thought the mass
was evenly distributed in
the atom
What he got
How he explained it
• Atom is mostly empty.
• Small dense,
positive piece
at center.
• Alpha particles
are deflected by
it if they get close
enough.
+
+
Density and the Atom
• Since most of the particles went
through, it was mostly empty space.
• Because the pieces turned so much,
the positive pieces were heavy.
• Small volume, big mass, big density.
• This small dense positive area is the
nucleus.
Rutherford Gold foil experiment movie
Bill Nye’s Greatest Discoveries
• Atomic Theory
• The electron
Size of nucleus, electron Start at 4:25
G:\Documents\Chemistry RJ Main\Honors\Honors 08 Unit
4\The_Structure_of_the_Atom_and_Atomic_Spectra.asf
World of Chemistry on-line video
• The Atom - first 16 minutes
Recreating Rutherford’s Experiment
Each box has a hidden shape,
Place a piece of paper on top
roll a marble into the hidden area of the box
Use a pencil to trace the marble’s path on the piece of paper
Use the path and anything you hear to help determine the shape
Repeat until you know what the hidden shape is
NO PEEKING OR FEELING to find the hidden shape
Turn in
3 pieces of paper stapled together with Names
Containing
marble paths
your guess for the actual shape
The shapes
Other particles
• Proton - positively charged pieces
1840 times heavier than the
electron – by E. Goldstein
• Neutron - no charge but the same
mass as a proton – by J. Chadwick
• Where are the pieces?
Subatomic particles – p.111
Name
Symbol
Charge
Relative
mass
(amu)
Actual
mass (g)
Electron
e-
-1
1/1840
9.11 x 10-28
Proton
p+
+1
1
1.67 x 10-24
Neutron
n0
0
1
1.67 x 10-24
Atoms contain 3 particles
e-
+
protons
Charge
neutrons
electrons
+1
0
-1
Mass
1 amu
1 amu
.0005 amu
Found
nucleus
nucleus
outer shell
If all atoms contain just protons,
neutrons, and electrons how can
atoms have different flavors???
Sulfur
Lead
Gold
Bromine
Neon
Counting the Pieces
• Atomic Number = number of
protons in the nucleus
• # of protons determines kind of
atom (which element it is)
• the same as the number of
electrons in the neutral atom.
• Mass Number = the number of
protons + neutrons.
• These account for most of mass
If an atom has an atomic number of 5 that
means it has 5 what?
5 protons
If it also has an mass number of 11 that
means it has 11 what?
11 (protons + neutrons)
How many neutrons???
Mass #
- Atomic #
# neutrons
11 protons + neutrons
- 5 protons
6 neutrons
Symbols
• Contain the symbol of the element (X),
the mass number and the atomic
number.
If the atom is neutral
then there is nothing
here
Mass
number
Atomic
number
X
Symbols
• Find the
9 – Atomic number
19 – Mass Number
9 – number of protons
10 – number of neutrons
9 – number of electrons
19
9
F
Symbols
 Find
the
35 –Atomic number
80 –Mass Number
35 –number of protons
45 –number of neutrons
35 –number of electrons
80
35
Br
Symbols
 if
a neutral atom has an atomic
number of 34 and a mass number
of 78 what is the
34 –number of protons
78
44 –number of neutrons
34
34 –number of electrons
–Complete symbol
Se
Symbols
 if
a neutral atom has 91 protons
and 140 neutrons what is the
91 –Atomic number
231 –Mass number
231
91 –number of electrons
91
–Complete symbol
Pa
Symbols
 if
a neutral atom has 78 electrons
and 117 neutrons what is the
78 –number of protons
78 –Atomic number
195
195 –Mass number
78
–Complete symbol
Pt
Ions
• If an atom does not have the same
number of protons and electrons it has a
charge
• These charged atoms are called ions
• The charge is usually indicated in the top
right corner of the symbol
32
S
16
2-
Does this ion have
more protons or
electrons??
Ions
• If an atom has more electrons than
protons it has a negative charge.
• If an atom has more protons than
electrons it has a positive charge
Net Charge
 1-
–10 p+ and 11 e 2–12 p+ and 14 e 1+
–45 p+ and 44 e–150 p+ and 147 e-  3+
Symbol Atomic # Mass #
23
+
11
Na
36
-
Cl
17
11
17
23
36
p+
11
17
# particles
in nucleus
n0
e-
12
10
1+
23
18
1-
36
19
Charge
Isotopes
• Dalton was wrong.
• Atoms of the same element can
have different numbers of neutrons.
• different mass numbers.
• called isotopes.
• All elements have different
isotopes.
• Isotopes are not necessarily
radioactive. But some are
Naming Isotopes
• Another way to name an isotope is to
name the element, then the mass #.
• carbon- 12
• carbon -14
• uranium-235
Comparing Isotopes
atomic # mass # protons neutrons electrons
• Carbon-12
• Carbon-14
6
12
6
6
6
6
14
6
8
6
Both carbon 12 and 14 behave the same in a chemical reactions. You
have many carbon atoms in you. Carbon-12 is not radioactive but
Carbon-14 is radioactive. Are you radioactive??
Other isotopes
• Hydrogen-1
• Hydrogen-2
• Hydrogen-3
“normal hydrogen”
deuterium
tritium
atomic # mass # protons neutrons electrons
• Hydrogen-1
• Hydrogen-2
• Hydrogen-3
1
1
1
0
1
1
2
1
1
1
1
3
1
2
1
If we have ten
marbles, and each
marble weighs 1 g,
what is the average
mass of the marbles?
1g
If we have two
marbles, and one
marble weighs 1 g
and the other
marble weighs 6g,
what is the
average mass of
the marbles?
3.5 g
If we have five
marbles, and one
marble weighs 6 g
and the other four
marbles weigh 1g,
what is the
average mass of
the marbles?
(6g x 1 marble) + (1g x 4 marbles) =
5 marbles
10 g
5 marbles
If we have five
marbles, and one
marble weighs 6g
and the other four
marbles weigh 1g,
what is the
average mass of
the marbles?
(6g x 1 marble) + (1g x 4 marbles) = 2 g/marble
5 marbles
Atomic mass
• What is it and why is it a decimal.
• Protons and neutrons both weigh 1 amu.
(mass of electrons is almost nothing)
• Chlorine’s atomic mass = 35.453 amu
Does Chlorine have a half a proton or half a neutron???
Atomic Mass
Most elements have more than 1 isotope in nature
Protactinium-216
217
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
•Different isotopes have different masses
because they have different #’s of _______
You need to gain
some weight
no
+
+
no
Hydrogen - 3
Hydrogen - 1
•Some of these isotopes are very rare.
(partially because some isotopes are very
unstable)
Some isotopes will only last a fraction of a second
•The atomic mass is an average based on the %
abundance of these isotopes in nature
If there are 10 boys and 20 girls in a room
What is the % abundance of boys?
10 / 30 *100% = 33%
Atomic Mass
• Chlorine has two common isotopes
35
Cl
17
Isotope mass =34.9689 amu
37
Cl
17
Isotope mass =36.9659 amu
• Notice that the actual mass (amu) of the
isotope is very close to the mass number
Atomic Mass
35
37
Cl
17
Isotope mass =34.9689 amu
Cl
17
Isotope mass =36.9659 amu
•If you were to go out and collect a sample of
chlorine atoms (say in a bucket of chlorine
bleach). You would find that there are some
of each isotope. More specifically it is always:
75.77 %
Cl-35
24.23 %
Cl-37
No matter where you collected the sample, you
would find that:
75.77 % are Cl-35
& 24.23 % are Cl-37
37
Cl
17
What is the
average mass?
35
Cl
17
Finding the atomic mass
% abundance as a decimal
(34.9689 amu*.7577 + 36.9659 amu*.2423)
26.50 amu
+
8.957 amu
= 35.457 amu
37
Cl
17
Notice the atomic mass is “weighted”
towards the more common isotopes
35
Cl
17
Atomic Mass
• Is not a whole number because it is
an average.
• The atomic mass is closer to the
mass of the most common isotope
• BUT NO chlorine atoms have a
mass of 35.45 because it is an
average.
If you have 1 marble that has a mass of 1 g
and another that has a mass of 2 g.
The average mass is 1.5 grams
How many marbles have a mass of 1.5 grams?
Copper has 2 Isotopes
63
29
62.93 amu
Cu
65
29
64.93 amu
Cu
The atomic mass of copper is
63.546.
Which isotope is more common?
How many copper atoms have a
mass of 63.546 amu?
Carbon has 2 (primary) Isotopes
12
6
C
12.000 amu
13
6
C
13.003 amu
The atomic mass of Carbon is 12.011
amu
Which isotope is more common?
How common is the other?
Magnesium has 3 isotopes
Mg-24
Mg-25
Mg-26
23.99 amu
24.99 amu
25.98 amu
78.9% abundant
10.0% abundant
The rest
What is the atomic mass of Mg?
Mg-24 23.99 amu
Mg-25 24.99 amu
Mg-26 25.98 amu
23.99 amu *.789 +
78.9%
10.0%
11.1%
Homework / Class work
SHOW ALL WORK
Gallium has 3 isotopes
Isotope
Isotope Mass
Abundance
Gallium-69
68.926
60.1%
Gallium-71
70.924
The rest
What is its atomic mass?
Silicon has 3 isotopes
Isotope
Isotope Mass
Abundance
Silicon-28
27.98 amu
92.23%
Silicon-29
28.98 amu
4.67%
Silicon-30
29.97 amu
remainder
What is its atomic mass?
It’s the number!!
The atomic number is the number of protons.
This is what determines the element. It is
often listed on the bottom left of the symbol.
The elements are listed in order of increasing
atomic number.
All atoms of helium have 2 protons
How many protons does a nitrogen atom have.
He
2
N
Most atoms are electrically neutral.
• If the atomic number of magnesium is 12.
How many electrons does it have.
Mg
What 2 particles make 99.98% of
the mass in an atom?
• The mass number is the number of
protons AND neutrons.
• It is often indicated on the top left of the
symbol
Mass #- protons and neutrons
24
Mg
12
atomic #- protons
# neutrons
12
Two ways to find the average mass
Simple Average
(34.969 amu + 36.966 amu) / 2
=
35.9677378 amu
Does this average reflect how many of each isotope would be
found in nature?
A recipe
1 Scoop Potassium Iodide (KI)
5 mL Soap
10 mL H2O2
%H
%O
H2O
11%
89%
H2O2
6%
94%
Distinguishing Between Atoms
• OBJECTIVES:
– Explain how the atomic number
identifies an element.
Distinguishing Between Atoms
• OBJECTIVES:
– Use the atomic number and mass
number of an element to find the
numbers of protons, electrons, and
neutrons.
Distinguishing Between Atoms
• OBJECTIVES:
– Explain how isotopes differ, and why
the atomic masses of elements are
not whole numbers.