chemistry review list the six major elements found in the human body. –carbon – 19.37%...
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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
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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)
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Atomic StructureOrbitals/shells contain electrons (e-) which determine the chemical reactivity of an element!
Nucleus contains protons and neutrons
(p+) (n0)
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Try this…
http://www.kscience.co.uk/animations/atom.htm
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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.
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Ions continued
• If an atom gains electrons, the atom becomes negatively charged (more negative charges than positive charges)This is called an anion
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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.
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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
136C 6 p+ 6 e- 7 n0 Carbon -
13
146C 6 p+ 6 e- 8 n0 Carbon –
14Unstable &radioactive
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Isotopes
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Half-life
• Time it takes for half of the radioactive nuclei to decay in a radioisotope.
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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.
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Carbon dating
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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.
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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
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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.
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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.
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Assignment
• Answer questions #16 on page 10 of your textbook.