Download Atoms and Atomic Theory

Atoms and their structure
History of the atom
Original idea Ancient Greece (400 B.C..)
Democritus Greek philosophers
History of Atom
Looked at beach
Made of sand
Smallest
possible
piece?
Atoms - not to be cut
Another Greek
Aristotle - Famous philosopher
All substances are made of 4 elements
Fire - Hot
Air - light
Earth - cool, heavy
Water - wet
Blend these in different proportions to get
all substances
His ideas were mostly opinion
Examples?
Can you think of examples to prove
invisible particles exist, even though we
can’t see them?
Who Was Right?
Greek society was slave based
Beneath Famous to work with hands
did not experiment
Greeks settled disagreements by
argument
Aristotle was more famous
He won
His ideas carried through middle ages.
Alchemists tried to change lead to gold
Who’s Next?
1808- John Dalton- England
Teacher- summarized results of his
experiments and those of other’s
In Dalton’s Atomic Theory
Combined ideas of elements with that of
atoms
Dalton’s Atomic Theory
1. All matter is made of tiny indivisible particles
(atoms)
Dalton was wrong here
2. Atoms of the same element are identical
3. Atoms can’t be subdivided, created, or
4.
5.
destroyed
Atoms of different elements combine in whole
number ratios to form compounds
Chemical reactions involve the
rearrangement of atoms.
Fundamental Laws of Chemistry
Dalton used “atoms” to explain the following laws:
Law of Conservation of Mass
1.
•
Number of reactants = number of products
Law of Definite Proportions
– Compounds have a constant composition by mass
– Every sample of water is made up of
2 H and 1 O; NaCl = 1 Na and 1 Cl
– Does not matter how many crystals of NaCl you
have
3. Law of Multiple Proportions
– If two elements make up more than one
compound, then the ratio of the elements will
always be a whole number ratio.
– H2O and H2O2 but not H2.3O0.7
2.
Analogy
A bicycle has 2 wheels, a tricycle has
three wheels. It’s a 2:3 ratio, a small,
whole number ratio
Now it’s your turn…
Laws of Multiple and Definete
Parts of Atoms
J. J. Thomson - 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, gas under low pressure
Why?
– Because without the pressure, the particles
will flow easier
Thomson’s Experiment
Voltage source
+
Vacuum tube
Cathode
Metal Disks
Anode
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 ray
appear to move from the negative to the
positive end
Thomson’s Experiment
Voltage source

+
Passing an electric current makes a ray
appear to move from the negative to the
positive end
Thomson’s Experiment
Voltage source

+
Passing an electric current makes a ray
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
Thomson’s Experiment
Voltage source
+
 By adding an electric field he found that the
moving pieces were negative
Thomson`s Model
Found the electron
Couldn’t find positive (for a
while)
Said the atom was like
plum pudding
Positive stuff, with the
electrons randomly
surrounding it
Like watermelon, the
seeds are spread
throughout and do not
contribute to the mass of
the fruit
Millikan- 1909
http://cwx.prenhall.com/petrucci/media
lib/media_portfolio/02.html
Discovered the
charge on the
electron
Gave it a unitCoulomb (C)
1.602 x 10-19 = q
(q stands for
charge)
1/2000 mass of
hydrogen
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 – He with pos. chargegiven off by uranium
Shot them at gold foil which can be made
a few atoms thick
Lead
block
Uranium
Florescent
Screen
Gold Foil
He Expected
The alpha particles to pass through
without changing direction very much
Because the positive charges were spread
out evenly. Alone they were not enough to
stop the alpha particles
What he expected
Because
Because, 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
“It was like shooting a bullet at a piece of
tissue paper and have the bullet reflect off
the paper back at you”
+
What Did It Prove?
The atom has a nucleus
Small, dense bundle of positive charge
Nucleus has a small volume compared to
the rest of the atom
Niels Bohr
1913
suggested that electrons in an atom
move in set paths around the nucleus
Much like planets orbit around the sun
Summarize
Create a table showing the experiment,
date and discovery from each of the
following:
– Millikan, Dalton, Thomson, Rutherford
Modern View
The atom is mostly
empty space
Two regions:
– Nucleus- protons
and neutrons
– Electron cloudregion where you
might find an
electron
Subatomic particles
Relative Actual
mass (g)
Name Symbol Charge mass
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
Size of an atom
Atoms are small.
Protons and neutrons = nucleus
Nucleus tiny compared to atom
If the atom was the size of a stadium, the
nucleus would be the size of a marble.
Radius of the nucleus near 10-15m.
Density near 1014 g/cm
What charge does the nucleus contain?
Flinn Mapping the Atom activity
Questions
Three compounds containing O and k
have 1.22g, 2.44g and 4.89g of K. Show
how this data supports the L.M.P.
Compare in terms of location, mass and
charge- electrons, proton and neutron
If I change the number of protons in a
substance, will it be the same substance?
Counting the Pieces
Atomic Number = number of protons
# of protons determines kind of atom
Same as the number of electrons in the
neutral atom
Atomic Mass = the number of protons +
neutrons (AKA Mass Number)
– All the things with mass
Symbols
Contain the symbol of the element, the
mass number and the atomic number
Mass
number
Atomic
number
X
Symbols
Find the
– number of protons
– number of neutrons
– number of electrons
– Atomic number
– Mass Number
19
9
F
Symbols
 Find
the
–number of protons
–number of neutrons
–number of electrons
–Atomic number
–Mass Number
80
35
Br
Symbols
 if
an element has 91 protons and
140 neutrons what is the
–Atomic number
–Mass number
–number of electrons
–Complete symbol
Ions
Atoms that have a different number of
electrons than they should have
– Gives the atom a charge
– Example: Carbon should have 6 electrons,
but C+ has 5 electrons. What charge does it
have?
Isotopes
Dalton was wrong again
Atoms of the same element
can have different numbers
of neutrons
– different mass numbers
– called isotopes
Example: Carbon-12;
Carbon-13
– Both have 6 protons
– Carbon-12 has a
relative mass of 12,
Carbon-13 has a
relative mass of 13
What’s Carbon-14?
Naming and Writing Isotopes
Put the mass number after the name of
the element
carbon- 12
carbon -14
uranium-235
To write them, Put protons on bottom and
mass number on top:
14
7
C
Question
How many p, e and n are in an atom of Cl37?
Mass number – atomic number = neutrons
37-17 = 20
17 p, 17 e, 20 n
Practice- Pg 80
Measuring Atomic Mass
Unit is the Atomic Mass Unit (amu)
One twelfth the mass of a carbon-12 atom.
Each isotope has its own atomic mass we
need the average from percent
abundance.
Can a single atom have an AMU?
Atomic Mass
Is not a whole number because it is an
average.
– The decimal numbers are on the periodic
table
It’s like calculating your grade- it’s made of
percentages that are weighted
Average Atomic Mass
How heavy is an atom of oxygen?
– There are different kinds of oxygen atoms.
= abundance of each element in nature.
Average of all the types of one element
Don’t use grams because the numbers
would be too small
Calculating averages
You have five rocks, four with a mass of 50
g, and one with a mass of 60 g. What is the
average mass of the rocks?
Total mass = 4 x 50 + 1 x 60 = 260 g
Average mass = 4 x 50 + 1 x 60 = 260 g
5
5
Average mass = 4 x 50 + 1 x 60 = 260 g
5
5
5
Calculating averages
Average mass = 4 x 50 + 1 x 60 = 260 g
5
5
Average mass = .8 x 50 + .2 x 60
80% of the rocks were 50 grams
20% of the rocks were 60 grams
Average = % as decimal x mass +
% as decimal x mass +
% as decimal x mass +
Atomic Mass
Calculate the atomic mass of copper if copper has two
isotopes. 69.1% has a mass of 62.93 amu and the rest has
a mass of 64.93 amu.
• (62.93*.691) + (64.93*?) = Answer
• How do you find ??
• 100-69.1 = 30.9%
• (62.93*.691) + (64.93*.309) = 63.548
• Check:
• Periodic table
• Sig Figs
• Label
Atomic Mass
Magnesium has three isotopes. 78.99%
magnesium-24 with a mass of 23.9850
amu, 10.00% magnesium-25 with a mass of
24.9858 amu, and the rest magnesium-25
with a mass of 25.9826 amu. What is the
atomic mass of magnesium?
Moles and Mass
One mole of an element is equal to it’s
mass AMU
Avegadro’s number is the number of
particles in one mole of that substance
Example- You have one mole of Pt, what
is it’s AMU?
Example- A mass of 2 g of Be contains
how many moles?
Review
How many p, e, n make up at atom of
carbon-13?
Write the symbol for oxygen-16
What’s the difference between isotope and
ion? Create an pneumonic device for this
difference.
Science Humor
A neutron walks into a bar. "I'd like a soda" he says. The
bartender promptly serves up a soda. "How much will that
be?" asks the neutron. "For you?" replies the bartender, "no
charge"
Q: What happens when electrons lose their energy?
A: They get Bohr'ed.
Q: What did the thermometer say to the graduated cylinder?
A: "You may have graduated but I've got many degrees"
A hydrogen atom came running into a police station asking for
help....
Hydrogen atom: "Someone just stole my electron!"
Policeman: "Are you sure?"
Hydrogen atom: "Yes, I'm positive"
Policeman: "Oh, I thought you were just being negative
again."