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Formation and uses of negative ions

Atoms Practice
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The Mass

How do we decontaminate?

License: CC BY-NC 3.0


Ever wonder how scientists are able to determine, for example, what pollutants are in the atmosphere or lakes?  Detect poisons in food?  One way to find out is to use cations and anions.  Because of their special bonding properties, specific cations or anions will be able to bond to specific molecules.  For example, if there was lead polluting a lake, add salt to the lake. 

Pb(OH)2 + 2NaCl  PbCl2 + 2NaOH

This will cause the lead to separate.

Creative Applications

  1. What are some other decontaminating examples you can think of?
  2. What could we use in place of the NaCl?



vs the Individual

Credit: cobalt123
Source: http://www.flickr.com/photos/cobalt/1308955915/sizes/m/in/photolist-2ZEJZr-3eXhC8-3LbnEa-3SYu9R-4969H3-49CXvm-49P2Wu-4caT6Z-4d11V7-4d19xC-4euQjB-4h2FKo-4jkW3E-4mXBHi-4mXBHF-4mXDt4-4sWDCv-4ueeN4-4viH6F-4vCYiQ-4yKPXb-4AHmfh-4AK6KG-4AUamz-4AUb5v-4B6sxK-4BkjG8-4BpAWS-4BpAZL-4C6Z3W-4CVnyS-4DA5uS-4DAaVS-4DS6yb-4GihWw-4HhuXw-4KUxBL-4KXPT3-4Qo5C8-4VS5iM-4VWkd3-4XUdrQ-4YdKD7-5amiPx-5bieb8-5bLpV8-5dbGQP-5dbH8K-5j942p-5kmVKD-5kPjh1/
License: CC BY-NC 3.0


The atomic mass listed on the periodic table is the average mass of the naturally occurring isotopes.  It is the average mass because all atoms are technically isotopes.  This is similar to how pennies are measured.  Because their compositions and therefore masses have changed over time, they are all a little bit different.   Pennies made at different times may have different metal content and pennies that are old and weathered differ from new pennies that are still in one piece.  To find the mass of the average penny, you would need to measure the mass of many different pennies. 

Creative Applications

  1. Try it out yourself.  Take some old pennies and measure them together and individually.  Do the individual measurements differ from the average?  (Note: it may take a very precise scale to see any significant changes.)
  2. What is the difference between accuracy and precision?
  3. Now that you have applied the idea of atomic mass, explain the difference between mass number and atomic mass.




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