The Atom

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Chapter 4

• The Atom Part 2

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Subatomic Particles
PARTICLE SYMBOL CHARGE MASS (amu) LOCATION
electron e- -1 ?0 orbit nucleus
proton p 1 ?1 inside nucleus
neutron n0 0 ?1 inside nucleus
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Alchemy The Golden Rule
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The number of protons in the nucleus of the atom
(atomic number Z) determines the atoms identity
Gold Atom Lead Atom
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Mass Number

• The sum of the protons and neutrons in the
  nucleus of an atom.

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What element is represented below?
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Carbon - 12

• This is the symbol for the isotope carbon-12.
• Atomic number is 6.
• Mass number is 12.

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Isotopes

• Isotopes are different types of atoms of a
  chemical element, having the same number of
  protons in the nucleus, but having different
  numbers of neutrons in the nucleus.
• Isotopes therefore have the same atomic number
  but different mass numbers.
• There are 275 isotopes of the 81 stable elements,
  in addition to over 800 radioactive isotopes, and
  every element has known isotopic forms.
• Isotopes of a single element possess almost
  identical properties.

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Isotopes
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Carbon - 12

• Write the symbols for carbon-13 and carbon-14.

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What is the average mass of a carbon atom?
12.01
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Atomic Mass

• The atomic mass of carbon is 12.01 amu.
• Atomic mass is the average mass of all the
  isotopes of an atom. It takes into account the
  different isotopes of an element and their
  relative abundance.

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What is the average atomic weight for chlorine if
it has two isotopes? The percent abundance for
chlorine-35 is 75.53. The percent abundance for
chlorine-37 is 24.40. The mass for Cl-35 is 35.0
amu and for Cl-37 it is 37.0 amu.

• (0.7553)(35.0 amu) (0.2440)(37.0 amu)
• 26.4355 9.028
• 35.4635
• the atomic weight of Cl 35.5 amu

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What is the average atomic mass for thallium, Tl?
The two stable isotopes and their abundances are
listed here.Tl-205 has a mass of 205.059 amu with
an abundance of 70.48 and Tl-203 has a mass of
203.059 amu with an abundance of 29.52  .

• 204.5 amu

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What is the average atomic mass for thallium, Tl?
The two stable isotopes and their abundances are
listed here.Tl-205 has a mass of 205.059 amu with
an abundance of 70.48 and Tl-203 has a mass of
203.059 amu with an abundance of 29.52  .

• (0.7048)(205.059 amu) (0.2952)(203.059 amu)
  
• 144.5256 59.943
• 204.4686
• the atomic weight of Tl 204.5 amu

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Common Uses of Isotopes

• Isotope Analysis
• Radiometric Dating
• Nuclear Medicine
• Magnetic Resonance Imaging (MRI)
• Positron Emission Tomography (PET scans)

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Importance of Isotopes
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Radiometric Dating
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Half-Life

• The decay of radioactive elements occurs at a
  fixed rate.
• The half-life of a radioactive isotope is the
  time required for one half of the material to
  degrade into a more stable material.
• Although the half-life pattern is the same for
  every radioactive isotope, the length of a
  half-life is different.
• For example, C-14 has a half-life of about 5730
  years while Ir-192 has a half-life of about 74
  days.

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Half-Life
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Carbon Dating
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Nuclear Medicine refers to imaging techniques
that use radioactive isotopes to detect and treat
disease. Magnetic resonance imaging (MRI) and
positron emission tomography (PET scans) are
examples.
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MRI PET scan
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MRI vs. PET

• Magnetic Resonance Imaging (MRI) is produced by
  measuring the magnetism of spinning electrons and
  protons and their interactions with nearby atoms
  when they absorb energy. This provides
  information about the chemical structure of
  organic molecules. MRI uses a magnetic field from
  super-cooled magnets and can often distinguish
  more accurately between healthy and diseased
  tissue. A contrast agent is usually used. MRI can
  provide pictures from various angles and
  construct a three dimensional image.Positron
  Emission Tomography (PET) scans measure emissions
  from positron-emitting molecules. Because many
  useful, common elements have positron emitting
  forms (carbon, nitrogen, and oxygen), valuable
  functional information can be obtained. The PET
  shows molecular function and activity not
  structure, and therefore can often differentiate
  between normal and abnormal (cancerous / tumor)
  or live versus dead tissue. PET scans are usually
  used to compliment rather than replace the
  information obtained MRI scans.

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• An atom of vanadium contains 23 electrons. How
  many protons does it contain?

• 23 p

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• An atom of silver contains 47 protons. What is
  its atomic number?

• 47

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• An atom of sodium contains 11 electrons. What
  is its atomic number?

• 11

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• An atom contains 37 protons. What element is it?

• rubidium

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• How many electrons, protons and neutrons are in
  an atom of actinium with a mass number of 221?

• 89p
• 89e-
• 132n0

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• How many electrons, protons and neutrons are in
  an atom of rhodium-105?

• 45p
• 45e-
• 60n0

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Homework

• Chapter 4 Worksheet 1