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					              Isotopes

…a little different, but really, all the same
                 Definition
• Isotope:
 Atoms of the same element that differ in their
  numbers of neutrons.
 Mass Number vs. Atomic Number
Mass Number:
• Number of protons + Number of neutrons

Atomic Number:
• Number of protons

How would you solve for the number of
 neutrons?
Mass number = number of protons + number of neutrons


                   A

                   Z
                     X            Element symbol




   Atomic number = number of protons

                 Isotopic Notation
           Average Atomic Mass
    …essentially an average of the different mass numbers in an element


• Some isotopes of an element are more
  common than others.
What’s the same? What’s different?
What’s the same? What’s different?
What’s the same? What’s different?
                  Isotopes
• Atoms of the same element, they’re just
  slightly different.
  - because they are still atoms of the same
  element, they help make up the average
  atomic mass                 Breakdown of              Carbon-
                                                          13
                                  Carbon Isotopes         1%


                      Carbon-14
                         0%




                                            Carbon-12
                                               99%
 Calculating Average Atomic Mass
• Multiply the average mass of each isotope by
  it’s percent abundance. You add up all these
  values to get the average atomic mass.
• Carbon ex.
Carbon-12 (12)X(0.9889) = 11.8668
Carbon-13 (13)X(0.011) = 0.143
Carbon-14 (14)X(0.0000000001) = 0.000000014
    (Average Atomic Mass) Total = 12.0098
                Basic Formula
           For Average Atomic Mass
Say you have an element with 4 isotopes:

(average mass #1)(#1 % abundance) = weighted average #1
(average mass #2)(#2 % abundance) = weighted average #2
(average mass #3)(#3 % abundance) = weighted average #3
(average mass #4)(#4 % abundance) = weighted average #4
     Add them all up to get the total = Average Atomic Mass

				
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posted:10/27/2011
language:English
pages:11