Download 2.05_BIO I_Isotopes_70

3.00_Chemistry of Biology
Biology I
(Isotopes)
Slides 70-82
1
Isotopes
All atoms of an element have the same number
of protons. However, they may have different
number of neutrons.
Atoms with the same number of protons and a
different number of neutrons are called isotopes.
An isotope is identified by its mass number,
which is the sum of the protons and neutrons in
the nucleus.
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What are Isotopes?
https://www.youtube.com/watch?v=EboWeWmh5Pg
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Isotopes Notation
https://www.youtube.com/watch?v=BYiu0kIWd30
4
Isotopes and Elements Practice Problems
https://www.youtube.com/watch?v=n4WZ0-fItt8
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Isotopes
• All the atoms of a particular element have the same number of protons. It is the
number of protons which determine the chemical properties of an atom. This is
because the number of protons determines the number of electrons which orbit
the nucleus. The number of neutrons however can vary.
• Atoms of the same element that have the same number of protons but
different number of neutrons are called isotopes of that element.
• Or in other words, atoms of the same element with the same atomic number
but different atomic masses are called isotopes of that element.
• The Three Isotopes of Hydrogen (H)
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Isotopes
•
•
•
Atoms of the same element that HAVE A
DIFFERENT NUMBER OF NEUTRONS
Some isotopes are radioactive. This means that
their nuclei is unstable and will break down at
a CONSTANT RATE over time.
There are several practical uses for radioactive
isotopes:
1. CARBON DATING
2. TRACERS
3. KILL BACTERIA / CANCER CELLS
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Isotopes: Different Forms of the Same Element
• In any element, the # of protons is always
constant.
• Unlike the number of protons, the number of
electrons and neutrons can vary within an
element without changing the identity of the
element.
– Ex. Carbon (C) ALWAYS has 6 protons, but it can
have anywhere from 6-8 neutrons and 2-10 electrons
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Isotopes
• An ISOTOPE is a form of an element that has a
different number of neutrons than “normal”
• Carbon has three isotopes
Notice how the # of
protons does NOT
change!
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Isotopes
• Atoms of the same element that have the same
number of protons and electrons but have a
different number of neutrons
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Isotopes
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Other Isotopes
• Most atoms have naturally occurring isotopes
including:
– Radon
– Potassium
– Uranium
• When an element is “radioactive” it means it has
an unstable number of neutrons (an unstable
ISOTOPE)
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Radioactive Isotopes
• When a nucleus breaks apart, it gives off
radiation that can be detected and used for many
applications.
• Examples include Carbon dating and radiation
therapy to treat cancer.
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Periodic Table on the Isotopes
• The elements, as they are found on the
periodic table, are neutral atoms and their
mass is an average of all isotopes
– Remember the atomic mass is the average of
ALL isotopes, but when we round it for
calculating the number of neutrons, we always
get the most abundant isotope.
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