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Isotopes and Nuclear Chemistry
We’ve learned that each element has its own
unique atom which is made up of a specific
number of protons. The number of protons
determines the atomic number of the
element. Each atom also has the same
number of electrons as protons. Isotopes
The three most stable isotopes of Hydrogen:
are atoms that have the same number of
Protium, the most common isotope of hydrogen, consists
protons and electrons, but a different
of one proton and one electron. ...
number of neutrons. Changing the number
A deuterium atom contains one proton, one neutron, and
one electron.
of neutrons does not affect the chemistry
Tritium atom contains one proton, two neutrons and one
of the element. It does, however, change
electron.
the mass of the element. Isotopes are
identified by their mass, which is the total number of protons and neutrons. There
are two ways that isotopes are generally written. They both use the mass of the
atom where mass = (number of protons + number of neutrons).
The first way is to put the mass as a superscript before the symbol of the
element: 4He, 14C, 235U
The other way is to write out the element and write the mass after a dash next to
the element's name: Helium-4, Carbon-14, Uranium-238.
Stable and Unstable Isotopes
Some isotopes are stable and happy. These are the elements that we see around
us and find in nature. Stable atoms generally have the same number of protons
and neutrons. Some accommodate one to two additional neutrons in the nucleus
and remain stable. However, when the nucleus of an atom possesses either too
many or too few neutrons compared to the number of protons it becomes
unstable. You see, positive charges repel each other – but the strong force
overcomes this electric force at small distances. The strong force is what allows
neutrons to “act like glue” keeping the right amount of spacing between the
positively-charged protons, and keep them from pushing each other out of the
nucleus. When there are too few neutrons, the protons are able to push each
other from the nucleus. When there is too many neutrons, this causes too much
spacing in between protons and the electric force overcomes the strong force.
Unstable isotopes also known as radioisotopes emit energy in the form of
radiation to restore the balance of protons to neutrons in the nucleus, this is
known as radioactive decay. The unstable isotope will decay over time and
eventually it will turn into another isotope or element.
Different Types of Radioactivity
There are three main types of radiation or radioactive decay depending on the
isotope: alpha decay, beta decay and gamma decay.
Alpha decay - Alpha decay is caused when there
are too many protons in a nucleus. In this case
the element will emit radiation in the form of
positively charged particles called alpha particles.
Alpha particles are considered not dangerous as
it can be stopped by a sheet of paper
Beta decay - Beta decay is caused when there
are too many neutrons in a nucleus. In this case
the element will emit radiation in the form of negatively charged particles called
beta particles. Beta decay is moderately
dangerous and can penetrate superficial
layers of skin tissue.
Gamma decay - Gamma decay occurs
when there is too much energy in the
nucleus. In this case gamma particles with
no overall charge are emitted from the
element. Gamma rays are the most
dangerous, these rays have the most
penetrating power. These extremely high
energy photons can travel through most
forms of matter because they have no mass. It takes several inches of lead -- or
several feet of concrete -- to effectively block gamma rays. If you're exposed to
gamma rays, they pass through your entire body, affecting all of your tissues
from your skin to the marrow of your bones.
What is the half-life of an isotope?
The half-life of an isotope is the time on average that it takes for half of the
atoms in a sample to decay. For example, the half-life of Carbon-14 is 5730
years. This means that if you have a sample of Carbon-14 with 1,000 atoms, 500
of these atoms are expected to decay over the course of 5730 years.
Some of the atoms may decay right away, while others will not decay for many
thousands more years. The thing to remember about half-life is that it is a
probability. In the example above, 500 atoms are "expected" to decay. This is not
a guarantee for one specific sample. It is just what will happen on average over
the course of billions and billions of atoms.
Why is radiation dangerous?
Radiation can alter the structure of cells in our bodies causing mutations which
can produce cancer. The more radiation exposure, the more dangerous it is.
Is some radiation good?
Despite the risks, a number of good ways that science has used radiation include
X-rays, medicine, carbon dating, energy generation, and to kill germs.