Transcript Nuclear Chemistry

Nuclear Chemistry
The nucleus is a tiny part of each
atom. How can it be the root of so
much energy release?
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Nuclear Chemistry
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To understand where all that energy comes
from, one must first know what constitutes the
nucleus of an atom.
The nucleus is the domain of protons and
neutrons.
Protons have a positive charge and are usually
balanced by electrons, which are found outside
the nucleus.
Neutrons have no charge.
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Nuclear Chemistry
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The number of protons in any atom’s nucleus is the
atomic number of that element.
Oxygen atoms always have 8 protons in the nucleus.
Gold atoms always have 79 protons in the nucleus.
How many protons would every atom of molybdenum
have?
If I have an atom with 49 protons in the nucleus, then it
is ________.
42, Indium
The number of protons gives the identity of the element.
Nuclear Chemistry
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http://www.theo-phys.uni-essen.de/tp/ags/guhr_dir/media/nucleus3.jpg
This is a nucleus with
30 protons and 42
neutrons. What
element is it?
It is zinc. Look at zinc
on your periodic
table. Its atomic
number is 30.
Zinc’s mass is also
listed. It is 70 amu.
Nuclear Chemistry
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This nucleus has 30 protons and 42
electrons. We know that any
nucleus with 30 protons is zinc.
What do the neutrons tell us?
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Protons + neutrons =
atomic mass
30 protons + 42 neutrons
= 72.
The periodic table
indicates that zinc’s mass
is approximately 70 amu.
Is this nucleus still zinc?
Yes!
It’s an isotope of zinc.
Nuclear Chemistry
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Nuclei can have different numbers of neutrons without
changing the identity of the element.
Atoms of an element with different numbers of neutrons
are called isotopes.
When you look at the periodic table of elements for the
mass of any element, you are finding the weighted
average of the masses of the naturally occurring
isotopes of that element.
The most common isotope of any element can be found
by rounding the given mass number to the nearest
whole number. Look at gallium. The most common
isotope of gallium is Ga-70. Why?
Isotopes – Nuclear Chemistry
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These are two common
isotopes of carbon.
C-12 is stable, and C-14
is radioactive.
Radioactive isotopes have
an unstable nucleus that
will decay.
What do the two isotopes
have in common?
Nuclear Chemistry
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Example: Let’s look at osmium.
of elements.
It’s right in the middle of your periodic table
An atom of osmium has how many protons?
I hope you said 76.
Osmium’s atomic mass is listed as 190.2. That means that most
osmiums probably have a mass of 190 amu, while a few have a
mass of 191 amu. They average out to 190.2 amu.
If I have a regular (most common) osmium atom, its protons and
neutrons must add up to 190. I know that there are 76 protons, so
the rest must be neutrons.
Protons + neutrons = atomic mass
76
+ N
= 190
How many neutrons are in a common osmium atom?
Nuclear Chemistry
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A regular osmium atom
has 114 neutrons and 76
protons, giving it a total
mass of 190 amu. That
isotope of osmium may
be called Os-190.
Another isotope could be
Os-194. That’s an
osmium atom with an
atomic mass of 194 amu.
How many protons and
neutrons would it have?
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Protons + neutrons = mass
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Do the math!
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Every osmium has ____
protons.
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76 + neutrons = 194
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Neutrons = 194 – 76
There are 118 neutrons in that
isotope.
Nuclear Chemistry
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You know that protons
are attracted to electrons
and vice-versa, because
opposite charges attract
electrostatically.
What holds the particles
in the nucleus together?
Protons repel other
protons.
Neutrons have no
If electrostatic repulsion had its
attraction for protons or way, the nucleus would fly apart!
for each other.
There must be another force at
work to hold a nucleus together.
Nuclear Chemistry
The strong force, also known as strong nuclear force, is stronger
than the electrostatic repulsion. It holds the nucleus together.
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Nuclear Chemistry
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Strong nuclear force holds all nuclei together,
but for some isotopes, the force is not enough.
These isotopes decay naturally.
Isotopes of any atom that can decay are called
radioactive.
C-14 decays over time at a predictable rate. It’s
so dependable that scientists use C-14 dating to
determine the age of many found objects. As it
decays, C-14 turns into C-12, a non-radioactive
isotope of carbon.
Nuclear Chemistry
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When we overcome the strong nuclear force,
energy is released.
A nuclear reaction is a reaction in which the
nucleus is changed and energy is released.
The only way to change the identity of an atom
is by changing the number of protons which are
in its nucleus. What kind of reaction could do
that?
Only a nuclear reaction can change the contents
of the nucleus.