NUCLEAR CHEMISTRY!!!
Boom, goes the nucleus
RADIATION
• Radiation is penetrating rays and/or
particles released by a radioactive
source.
• A good example of radiation is UV
rays from the sun.
• As you know, these uv rays penetrate
your skin to tan, burn, or even cause
cells to malfunction and produce
cancer cells
RADIOISOTOPES
• Radioisotopes are isotopes that have an
unstable nucleus and, thus, undergo
radioactive decay.
• The reason a nucleus would be unstable
is because it either does not have
enough neutrons or has too many.
• A nucleus has protons in it. If they were
there by themselves, then what would
happen?
• So neutrons are kind of the glue holding
all those protons together.
• If there is not the correct ratio of protons
to neutrons, then the nucleus will be
unstable.
RADIOACTIVE DECAY
• An unstable nucleus will cause an atom of an
element to decay, or fall apart, and form new
elements.
• For instance Carbon-14 falls apart or decays to
form Nitrogen-14.
• These unstable radioisotopes fall apart at a
uniform (consistent) rate measured in half-lives.
• Scientists can use the half-lives to figure out the
age of substances containing these unstable
radioisotopes.
HALF- LIVES
•
A half life is the amount of time it takes for a substance to decay half way.
• So the substance loses half of what it has each half life. This is easier
understood by seeing it.
Half lives
Amount of substance
Beginning amount
96 grams
After 1st half life
48 grams
After 2nd half life
24 grams
After 3rd half life
12 grams
After 4th half life
6 grams
• Different substances have different half-lives:
• Carbon-14 = 5730 years
• Uranium-235 = 703.8 million years
• Iodine-131 = 8 days
HALF LIVE PROBLEMS
• A substance has a half-life of 30 years:
• If we started with 32 grams and now only have 2 grams left, how old is
the substance?
• 32/2= 16 16/2=8 8/2=4 4/2=2, so that’s four half lives
• 4 half-lives x 30 years = 120 years
• If we start with 96 grams, how many grams are left after 210 years?
• 210 years/30 years in a half-life = 7 half-lives
• 96/2=48 48/2=24 24/2=12 12/2=6 6/2=3 3/2=1.5 1.5/2=0.75g
MORE HALF-LIFE PROBLEMS
• What is the half-life of H2O2?
• You start at about 230, so half is 115. Draw a line straight to the surve from 115.
• Draw a line straight down from where you hit the curve, and that will tell you the
half life.
• In this case, the half-life is about 27 seconds.
MORE HALF-LIFE PROBLEMS
• If 20% of the original H2O2 remains, how much time has gone by?
• You start at about 230, so 20% is 46. Draw a line straight to the curve from 46.
• Draw a line straight down from where you hit the curve, and that will tell you how
much time has gone by.
• In this case, the time gone by is about 60 seconds.
ALPHA PARTICLES
• Alpha particles are released from radioactive
nuclei.
• The alpha particle is identical to a helium atom
nucleus, having two protons and two neutrons
• The alpha particle can be symbolized by the
greek letter alpha: α
• Or it can be symbolized by the notation for a
helium nucleus:
• Alpha particles have comparatively little energy
and cannot even penetrate a piece of paper
BETA PARTICLES
• Beta particles result from breaking apart neutrons in
an atom.
• Beta particles are electrons released when a neutron
breaks apart. The beta particle (electron) escapes
while the other part of the neutron now forms a proton
that stays in the nucleus
• Beta particles can be symbolized by an electron:
• Or they can be symbolized with the greek letter beta:
• Beta particles (electrons) are much smaller than
alpha particles so they can penetrate further with
higher energy, but can still be stopped by aluminum
foil or wood.
GAMMA RAYS
• Gamma rays are often released during radioactive decay.
• Gamma rays have no mass: They are pure energy.
• Though we say mass is conserved in nuclear reactions, on a very, very,
very, very small scale some mass is lost.
• This very small amount of mass is converted into energy.
• Ever seen this before?
• E = mc2
• The very small mass “lost” is converted into lots of energy in the form of
gamma rays.
• The symbol for gamma rays is the greek letter gamma: ϒ
• Gamma rays are extremely high energy and can penetrate most anything.
ATOMIC REACTIONS
• Nuclear bomb video
• And another
STRONG NUCLEAR FORCE
• This is the force, helped by the neutrons, that is
holding the nucleus together
• Remember that the protons are repelled by each
other due to them all being positively charged.
• The strong nuclear force is stronger than the
repelling force so it holds the nucleus together.
BAND OF STABILITY
• If an isotope falls in the
band of stability.
• It has the correct ratio
of neutrons to protons
• And its nucleus is
stable.
• If an isotope falls outside
of the band of stability
• It has a “bad” ratio of
neutrons to protons
• And its nucleus is
unstable
NUCLEAR FISSION
• Fission is when the nucleus of an atom is split
apart
• Fission is the type of nuclear reaction used in
nuclear energy plants.
• When the atom is split, some mass is ”lost”
and … remember Einstein???
• The “lost” mass is actually converted into
energy.
NUCLEAR FUSION
• Nuclear fusion happens when the
nuclei of atoms combine (fuse)
• In fusion, some of the mass is “lost”
when the nuclei join together.
• So, remember Einstein again? The
“lost” mass is converted into energy.
• All of the other elements in the
universe are a result of hydrogen
undergoing fusion in stars and
producing helium.
FUSION AND (SIMPLIFIED) ELEMENT MAKING
•
Fusion occurs inside stars
• 4 Hydrogen atoms fuse in
order to produce helium and
gamma rays
• 3 Helium atoms fuse in order
to produce carbon atoms.
Fusion in stellar cores
• A carbon atom fuses to a
helium atom in order to make
oxygen.
• This goes on until iron is
formed.
•
The elements larger than iron are
formed when stars explode
(supernovas).
Fusion in supernova explosions