Download So why are some isotopes stable and some unstable (radioactive)

#3
Strong nuclear force is a very strong
force of attraction given off by all nuclear
particles which acts over a very small
distance. This attempts to hold the nucleus
together.
Electrostatic force. It is much weaker
than the SNF but acts over a much larger
distance. Only acts on charged particles.
In the nucleus where all of the charged
particles have a similar charge, the EMF
attempts to push the nucleus apart.
#5
The primary factor in determining nuclear
stability is the PROTON : NEUTRON
RATIO.
The most stable ratio is about 1:1 for small
atoms, and gradually increases to about
1:1.5 for larger atoms. See pg 866.
A secondary cause for a nucleus to be
unstable is the nucleus being to
large…BISMUTH-209
If a particle has more than 83 protons or a
mass number greater than 209 it is too big
to be stable
# 9. Isotopes not in the band of stability
undergo spontaneous changes
(transmutations) to other, more stable,
isotopes.
# 10:
Certain isotopes for each element are
stable…these do not change. Other
isotopes are unstable (we call them
radioactive isotopes or radioisotopes).
# 12 Radioactive decay is when an
unstable nucleus shoots out (radiates)
small pieces of their nuclei (radiation).
#13
Alpha decay: Nucleus too big
mass=4 amu charge = +2
Beta decay: Too many neutrons per proton
mass = 0 charge = -1
Positron decay: Too few neutrons per proton
mass = 0 charge = +1
Electron capture: Too few neutrons per proton
mass = 0 charge = -1
Gamma Ray: accompanies all other nuclear
changes no mass or charge just energy
# 16. We find mainly stable isotopes,
because over the eons, unstable ones
have transmuted themselves into stable
ones. We call these transmutations
nuclear changes or nuclear reactions.
Over time there will be less and less
radioactive material in nature because it is
constantly decaying into stable material.
In a nuclear reaction, the identity of the
elements can change, but the total mass and
amount of charge must stay the same. To
ensure that our representative equation shows
this we must balance our nuclear equations.
To do so we must:
a. Write the chemical symbol for all reactants
(things as they exist before the change) and
products (things as they exist after the change)
separated by an arrow including their atomic
number written as a subscript to the left of the
symbol, and their atomic mass written as a
superscript to the left of the symbol.
b. Ensure that the total atomic numbers on both
sides of the equation (arrow) are equal, and that
the total atomic masses on both sides of the
equation are equal.
--They have too little Binding Energy per
nucleon
When an atom forms from sub-atomic
particles, the atoms weigh less than the
sum of the particles. This “lost” weight
(mass defect) is converted to energy
according to e=mc2. This energy must be
replaced to each nucleon in order for an
atom to break apart, so the lower this
energy per nucleon, the more unstable the
isotope.
Synthetic (man-made) decay
We can cause isotopes otherwise stable
isotopes to decay by shooting them with
small nuclear particles. They will usually
give off protons, or neutrons, or both.
These particles which are given off can
then create a self sustaining decay if their
is enough of the original isotope. (critical
mass)