CHEMISTRY REVIEW
•List the six major elements found in the human body.
–Carbon – 19.37%
–Hydrogen – 9.31%
–Nitrogen – 5.14%
–Oxygen – 62.81%
–Phosphorus – 0.63%
–Sulfur – 0.64%
Remember an element is a substance that can not be
broken down into simpler substances by ordinary
chemical means
The smallest part of an element that retains
the elements properties is an atom.
Standard atomic notation
M = mass number
(protons + neutrons)
E = element
A = atomic number
[number of protons (p+) in an
atom]
Determines the identity of an
atom!
NOTE: Mass number – atomic number = number of neutrons (n0)
Atomic Structure
Orbitals/shells contain electrons (e-)
which determine the chemical
reactivity of an element!
Nucleus contains protons and neutrons
(p+)
(n0)
Try this…
http://www.kscience.co.uk/animations/atom.htm
Ions: changing the number of electrons
in an atom (mass and atomic number remain
unchanged)
• An atom that carries an electrical charge is
called an ion
• If the atom loses electrons, the atom
becomes positively charged (because the
number of positively charged protons will be
more than the number of electrons)
This positively charged ion is called a cation.
Ions continued
• If an atom gains electrons, the atom
becomes negatively charged (more negative
charges than positive charges)
This is called an anion
Ions in biological systems
• H+ (hydrogen ions) are critical to the process
of cellular respiration.
• Na+ are part of transport mechanisms that
enable other molecules to enter cells
• Na+ and K+ are critical to nerve impulses
• Ca2+ is critical to neurotransmitter release or
muscle functioning.
Isotopes
• Atoms with the same atomic number (p+) but different
atomic masses.
• Thus they contain a different number of neutrons but
the same number of protons and electrons.
(p+)
(e-)
(no)
12
6C
6 p+
6e-
6n0
Carbon - 12
13
6C
6 p+
6 e-
7 n0
Carbon - 13
14
6C
6 p+
6 e-
8 n0
Carbon – 14
Unstable &
radioactive
Isotopes
Half-life
• Time it takes for half of the radioactive nuclei
to decay in a radioisotope.
Useful Applications of Radioisotopes
1. RADIOMETRIC DATING: radioactive
isotopes decay at a predictable rate
– Living organisms have the same amount of
C-12 and C-14 as in the atmosphere.
– When an organism dies C-14 starts decaying
to C-12 at a constant rate.
– Scientists measure the ratio of C-12:C-14 in
dead fossilized organisms to predict time of
death.
Carbon dating
Useful Applications Radioisotopes
continued
2. Radioactive Tracers: Radioisotopes are
used to follow chemicals through chemical
reactions and trace their path as they move
through cells/bodies of living organisms.
This has applications in biological, chemical,
and medical research.
Example 1: Thyroid Gland
• The thyroid gland uses iodine to make
hormones that influence growth and
metabolism.
– Doctors administer radioactive iodine-131,
and then use a photographic device to trace
the radiation
Example 2: Using positron emission
tomography (PET) to diagnose cancer
tumours
• Cancerous tissues are characterized by a much
higher level of activity than healthy tissues.
• Thus cancer cells take in more glucose – a common
cellular energy source – than healthy cells.
• If a patient is injected with radioactive glucose and
then a PET scan can be done to determine the
location of a cancerous tumour.
Questions to consider
1. What radionuclide tends to be used for PET scans
in place of glucose?
2. What happens to glucose when it is taken up by a
cell? What happens to the modified molecule that
is taken up by the cells?
3. What is a positron?
4. What other imaging techniques are often used
with PET scans?
5. What is the generalized half life of the
radionuclides used in PET scans? Explain.
Assignment
• Answer questions #16 on page 10 of your
textbook.