Download Lesson 5: Current Atomic Model

December 15, 2011
The Atom
chapter 16
Lesson 1
Objective
You will be able to
identify the particles that make up the atom
Define mass defect and binding energy.
Introduction - story
A stranger was seated next to a girl on the airplane
when the stranger turned to her and said,
"Let's talk. I've heard that flights go quicker if you strike
up a conversation with your fellow passenger."
The girl, who had just opened her book, closed it slowly
and said to the stranger,
"What would you like to talk about?"
Oh, I don't know", said the stranger. "How about nuclear
power?"
December 15, 2011
"OK," she said. "That could be an interesting topic. But
let me ask you a question first. A horse, a cow, and a
deer all eat grass, the same stuff.
Yet a deer excretes little pellets, while a cow turns out a
flat patty, and a horse produces clumps of dried grass.
Why do you suppose that is?"
The stranger thinks about it and says,"Hmmm, I have no
idea,"
To which the little girl replies,
"Do you really feel qualified to discuss nuclear power
when you don't know shit?"
December 15, 2011
What is in the nucleus?
Rutherford’s Model (about 1900)
Nucleus with a net positive charge surrounded by negative
electrons in orbit.
During the 1930’s protons and neutrons discovered.
Charges are the same magnitude but opposite sign for protons
and electrons, neutrons have no charge.
Atomic Mass Units
Dealing with numbers such as 9.11 x 10-31 kg is a little
cumbersome. For this reason, scientists that work with the
nucleus deal in terms of atomic mass units (u). These are
defined as exactly 1/12 of the mass of carbon-12
1u = 1.66x10-27 kg= 931.5 MeV/c2
See your data table for mass of the electron in MeV/c2
December 15, 2011
Atomic notation
Atomic Mass in
amu's
Atomic
Number
A
X
Z
element's
symbol
Atomic mass consists of the sum of the protons and the
neutrons
protons (Z) + neutrons = atomic mass (A)
Calculate the number of protons, neutrons and mass of the
fluorine atom.
Note: the protons and neutrons are collectively called
nucleons.
19F
9
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Isotopes
Elements can have atoms that contain the same number of
protons but have different masses. The difference is due to
the different number of neutrons in the nucleus. These are
called isotopes.
One example is carbon. It has three main isotopes.
12
6C
Carbon - 12
13
C
6
Carbon - 13
14
C
6
Carbon - 14
Ions
Ions are charged particles. The atoms that have a different
number of electrons than protons, resulting in a net charge.
These do not affect nuclear calculations!
December 15, 2011
What holds these particles together?
The strong nuclear force is a fundamental force that is great
enough to overcome the repulsion forces of the nucleus.
When all of the masses of the individual components of the
atom are added together, it is found that it is more than the
mass of the atom. It is believed that the missing mass is
present in the energy that holds the nucleus together. This is
called the BINDING ENERGY.
Example: deuterium
Calculate the binding energy of deuterium.
Mass of neutron = 1.67492 x 10-27 kg
2
H
1
Mass of proton = 1.67262 x 10-27 kg
Mass of deuterium nucleus = 3.34432 x 10-27 kg
Calculate the theoretical mass of a deuterium atom by adding
the mass of a neutron and the mass of a proton
December 15, 2011
Calculate the difference in the theoretical mass from the
actual mass by subtracting the two values.
Calculate the binding energy of the deuterium nucleus using
E=mc2
Assignment
Read p. 790-796
Do p. 796 #8,9,10
Do SNAP p. 350 all and p. 367 all
Answers
p. 237
2a) hydrogen b) cobalt c) iron d) gold e) strontium
p. 345
2: a) 1.828 x 10-28 kg b) 1.65 x 10-11 J c) 1.18 x 10-12 J
4: 9.9879 x 10-27 kg