Download File

Nuclear
Chemistry
Lesson 1
Atomic Notation
• Recall, we learned atomic notation.
• A nuclide is the nucleus of a specific
atom.
• The radioactive nuclide strontium-90 has
90 protons and neutrons. The atomic
number is 38.
Sr
90
38
Radioisotopes
• The nuclei of unstable
isotopes gain stability by
undergoing changes and
emitting large amounts of
energy (radiation)
• Nearly all isotopes with
atomic number of 84 or
greater are unstable
Band of Stability
and Radioactive
Decay
Transmutation
The conversion of one atom to another is
transmutation
• Artificial Transmutation – particles
bombard the nucleus of an atom forcing
a change.
• Natural Transmutation – the nucleus of
an atom undergoes radioactive decay
due to an imbalance between the
number of protons and neutrons in a
nucleus. Unstable atoms will decay
until they create more stable atoms.
Mass Defect (Deficit)
• Some of the mass in the nucleus
can be converted into energy
(less than the mass of an proton)
• Shown by a very famous equation!
2
E=mc
Energy
Mass
Speed of light (a rather large number) ≈ 3 x 108 m/s
•In all nuclear reactions, some amount of
mass is lost and converted into energy
Mass Defect
Difference between the mass of
an atom and the mass of its
individual particles
4.00260 amu
4.03298 amu
Nuclear Reactions vs.
Normal Chemical Changes
• Nuclear reactions involve the nucleus.
The nucleus opens, and protons and
neutrons are rearranged.
• The opening of the nucleus releases a
tremendous amount of energy that
holds the nucleus together – called
binding energy
• “Normal” Chemical Reactions involve
electrons, not protons and neutrons,
therefore, comparatively little energy is
gained from these reactions.
Types of Radiation
•Alpha (ά) – a positively
charged helium nucleus
•Beta (β) – a.k.a. electron
4
He
2
4
2
2 0
He
1 e
•Gamma (γ) – pure energy; 0 1
0
1
called a ray rather than a
0
particle – has no mass or
0 0
charge
0
e

Other Nuclear Particles
1
•Neutron
0n
1 0
• Positron – a positive
00
particle, same size as 1 e
0 1
an electron
1
1
•Proton – usually
1 H
1
1
referred to as
1
hydrogen-1
n
e
H
•And many other
elemental isotopes
Charge of Radiation Types
• Alpha particles have a +2 charge,
and beta particles have a –1 charge.
Both are deflected by an electric
field.
• Gamma rays are electromagnetic
radiation and have no charge, so
they are not deflected.
Penetrating Ability
• Video
Behavior of Radiation
• Since alpha particles have
the largest mass, they are
the slowest-moving type of
radiation.
• Gamma rays move at the
speed of light since they
are electromagnetic
radiation.
Alpha Radiation
• An alpha particle (a) or helium nucleus
(42He) is emitted
• Each particle contains 2 protons, 2
neutrons and has a +2 charge (not
usually written)
238 U
92

234 Th
90
+
4 He
2
Note that the equation is balanced.
The sum of the mass numbers & atomic
numbers are equal.
Beta Radiation
• A beta particle (b) or electron (0-1e) is
emitted
• A neutron breaks apart into a proton,
which remains in the nucleus, and an
electron, which is released
14 C
6

14 N
7
+
0
-1e
Note that the equation is balanced.
The sum of the mass numbers & atomic
numbers are equal.
Gamma Radiation
• A gamma particle () or high energy
photon is emitted (light)
• Gamma rays have no mass, no p+
and no no so they do not alter
atomic mass or atomic number.
• It is PURE ENERGY which explains
the large penetrating power of 
rays.
• They are often emitted along with
alpha or beta particles
230 Th  226 Ra + 4 He + 
90
88
2
Electron Capture
• A few large, unstable nuclides decay
by electron capture. A heavy,
positively charged nucleus attracts
an electron.
• The electron combines with a proton
to produce a neutron.
• Lead-205 decays by electron
capture.
205
82
Pb +
0
-1
e
205
81
Tl
Balancing Nuclear Reactions
•
•
•
•
The total of the atomic numbers
(subscripts) on the left side of the
equation must equal the sum of the
atomic numbers on the right side.
The total of the atomic masses
(superscripts) on the left side of the
equation must equal the sum of the
atomic masses on the right side.
After completing the equation by writing
all the nuclear particles in an atomic
notation, a coefficient may be
necessary to balance the reaction.
Use a particle or isotope to fill in the
missing protons and neutrons.
Practice Problem
Write the nuclear equation for the
alpha decay of gold-185.
185 Au
79

181 Ir
77
+
4 He
2
Practice Problem
Fill in the blank.
214 Po
84
214At
85
 ___
+
0 e
-1
+
Practice Problem
Fill in the blank.
214
4 He + 2 0 e 
Po
+
2
84
2
-1
222Rn
86
___________
Practice Problem
What radioactive isotope is
produced in the following
bombardment of boron?
10B
5
+
4He
2
13N
7
_____
+ 1n
0