Transcript Nuclear Chemistry

Nuclear Chemistry
ATOMIC REVIEW:
• Atomic number
= # of protons
• # of neutrons
= mass # - atomic #
• protons & neutrons are in
the nucleus
ATOMIC REVIEW:
• isotopes have different # of
neutrons
• there are 3 forms of isotope
notation
carbon-12
12
6
C
12
C
ATOMIC STRUCTURE
• Nucleon = term for all protons & neutrons
• Strong nuclear force
• short-range force among nucleons
– Increases with shorter distance
– NOT the same as an electric force
Stable vs. Unstable
• Stable nuclei
no spontaneous changes
• Unstable nuclei
spontaneously changes to become
a nucleus of a different element
Transmutation
• Unstable nuclei are naturally
“built wrong” and “fall apart”
• An unstable nucleus undergoes
transmutation, changing from
one element into another
– the nucleus changes # of protons!
Why?
• Radioactivity of an atom depends
on the ratio of neutrons (N) to
protons (P)
• How is a nucleus held together?
 STRONG NUCLEAR FORCE
Why?
• Think about it! . . . protons are all
positively charged and want to repel
each other
• Neutrons act as a “nuclear glue” –
they increase the strong nuclear
force but don’t repel because they
have no charge
Band of Stability
• N/P ratio of stable nuclei
• Stable small atoms (atomic # less
than 20) are near 1/1 ratio
• Stable large atoms are near 1.5/1
ratio.
• Predict the stability of the following:
carbon-12
mercury-200
hydrogen-3
uranium-238
Discovery
– In the 1900’s only 3 radioactive
elements were identified
– Today, all elements after bismuth
are radioactive
– The larger they are, the more
easily they “fall apart”
Radiation Types
1.
2.
3.
4.
5.
Alpha () particles
Beta () particles
Gamma () rays
Positron emission
Electron Capture (EC)
. . . and more
Nuclear reactions have BALANCED
nuclear equations!!
 (alpha) Particle
• it is a helium nucleus
4
4
• symbol: 2 He or 2 
• low energy – doesn’t penetrate foil
• decreases the # of protons
• never emitted with beta
210
84
Po 
206
82
Pb +
4
2
He
 (beta) Particle
•
•
•
•
•
it is an electron (from the nucleus)
0
0
symbol: -1 e or -1 
higher energy - penetrates the skin
increases # of protons
never emitted with alpha
14
6
C 
14
7
N +
0
-1
e
 (gamma) Ray
• high energy electromagnetic wave
• no mass and no charge
• higher energy – blocked only by
thick lead or thick concrete
• used to treat cancer
• usually is emitted with alpha or beta
238
92
U 
4
2
He +
234
90
Th +

0
0
Positrons or Electron Capture
0
+1
• Positron emission  e
– decreases # of protons
– (product side of equation)
• Electron Capture, EC  e
(reactant side of equation)
0
-1
• Neutron captured or emitted  n
1
0
Fission & Fusion
• Nuclear Fission – the splitting of a nucleus
into fragments
– Very large release of energy
– Used in nuclear power plants
• Nuclear Fusion – the combining of atomic
nuclei
–
–
–
–
Very large release of energy
Occurs in the core of the sun & other stars
Requires high temperatures (5 million K)
Atomic explosions initiate fusion, but can’t be
controlled
Fission & Fusion
• Nuclear Fusion – the combining of
atomic nuclei
– Very large release of energy
– Occurs in the core of the sun &
other stars
– Requires high temperatures (5
million K)
– Atomic explosions initiate fusion, but
can’t be controlled