Isotope Class Notes
Subatomic Particles
• Label the atom:
What are Isotopes?
• First, do you remember how to find the
number of neutrons in an atom?
• Write the equation down in your notes
What are Isotopes
• Isotopes are atoms that have a different
number of neutrons.
• An atom is still the same element if it
has different neutrons - it’s just a
different version!
• Neutrons can be added to an atom
without altering the number of protons
and electrons it has.
• http://www.youtube.com/watch?v=YYI
nVraBe7s A Heavy Water Experiment
Carbon Isotopes
• For example, the element carbon has 13
different isotopes!
• You are familiar with C-12 (the C stands
for carbon, and the 12 is it’s atomic
mass)
– This isotope has 6 neutrons
• C-14 (atomic mass 14) is used for
carbon dating and has 8 neutrons!
More about Isotopes
• In an isotope, the number of protons
and electrons never changes- only the
number of neutrons is different
• This means that each isotope of a
particular element has a different atomic
mass than another isotope of the same
element
– Remember: C-12 has an atomic mass of 12
and C-14 has an atomic mass of 14!
Count the Number of Protons and Neutrons
Isotope Notation
• There are several different ways to write
symbols for isotopes, each of which is
perfectly legitimate.
The other ways to write each
of these hydrogen isotopes
from top to bottom are:
Hydrogen-1 or H-1
Hydrogen-2 or H-2
Hydrogen-3 or H-3
Example
Write down the three different notations for a carbon atom with 6
protons and 6 neutrons.
Applications of Isotopes
• Carbon dating
• Carbon-14 is created by the
bombardment of the atmosphere by
cosmic rays. It is an unstable radioactive
isotope of C-12. After creation it finds its
way into living organisms. When an
organism dies no more C-14 is added and
what C-14 is present continues to decay.
To date artifacts scientists compare the
number of C-14 atoms to the more
common C-12 atoms in the artifact. This
ratio along with the half-life of
radioactive C-14 allows dating to occur.
Applications of Isotopes
• Structural determination of
compounds
– Isotopes are used to trace the formation
of structures by acting as labels.
• Medical Uses
– Isotopes are used for diagnosis in
medicine.
– Sodium-24 used to trace blood flow in
the body so that obstructions can be
detected.
– Iodine-131 has been used to test the
activity of the thyroid gland
Chemistry in the Environment
• The processing of uranium ore for
nuclear fuel produces large amounts of
radioactive mill tailings. Until the late
1970’s disposal of the radioactive
tailings was not controlled. As a result ,
millions of tons of these radioactive
tailings are present in unmarked sites
across the United States and Canada.
Quick Activity
•
1)
2)
3)
4)
5)
Calculate the number of neutrons there
are in the following isotopes (use your
periodic table to find the atomic
numbers)
Carbon-14
Nitrogen-15
Sulfur-35
Calcium-45
Iodine-131
Calculating Atomic Mass Based on Isotopes
• Most elements exist as several different
isotopes. For example, chlorine has two
naturally occurring isotopes:
chlorine-35
chlorine-37
• 75.77% of the chlorine in the world exists
as chlorine-35, and 24.23% exists as
chlorine-37.
Calculating Atomic Mass Based on Isotopes
• This is why the atomic masses on the
periodic table are not WHOLE numbers.
• If we know how much of each isotope
exists in the world, we can calculate the
average atomic mass of that element
(which is the number you find on the
periodic table).
Example:
Chlorine exists as two different isotopes,
chlorine-35 and chlorine-37. Given that
75.77% of chlorine is chlorine-35 and
the other 24.23% is chlorine-37,
calculate the average atomic mass of
chlorine.