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Isotopes    •  Have  same  chemical  proper/es  

–   (determined  by  #  electrons)  

•  All  isotopes  of  an  element  have  the  same  atomic  number  (#P)  

Atomic  Mass  of  an  Element    •  An  average  of  the  masses  of  all  naturally  occurring  isotopes  mul/plied  by  the  abundance  of  each  isotope  as  a  decimal  

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Calculating average atomic mass for Carbon

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Uses  of  Isotopes  •  Food  irradia/on    •  Archeological  da/ng  •  Smoke  detectors  •  Radioac/ve  tracers    

Calcula/ng  Average  Weighted  Atomic  Mass  

•  Must  know:  –   1)  number  of  isotopes  – 2)  mass  of  each  isotope  – 3)  natural  percent  abundance  of  each  isotope  

•  Calcula/on:  – Mul/ply  mass  of  each  isotope  by  natural  abundance,  express  as  decimal  and  add  products  

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Radioac/ve  Isotopes    &  Nuclear  Chemistry    

•  Study  of  the  produc/on  and  use  of  radioac/ve  sources  for  medicine,  industry,  spacecraP    

What  causes  atoms  to  be  radioac/ve?  •  An  atom  with  an  unstable  nucleus,  where  the  nucleus  has  an  excess  of  internal  energy  (too  many  neutrons  or  protons)  

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Radioac/ve  Decay  •  The  process  when  an  unstable  nucleus  emits  radia/on  (disintegrates),  turning  into  new  element  

•  May  eject  neutrons  or  protons  •  Convert  one  subatomic  par/cle  to  another  •  Releasing  energy  (gamma  rays)  

Radioac/ve  Isotopes  (radioisotope)  •  Unstable  nuclei,  dissipate  excess  energy  by  emiUng  radia/on  in  the  form  of  alpha,  beta,  and  gamma  rays    

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Radiocarbon  Da/ng  •  C-­‐14  Da/ng:  Can  determine  age  of  biological  sample  (wood,  bones,  teeth)  

Da*ng    Organic  Material  Using  Carbon  14  •  Ra*o  of  Carbon  14  (radioac/ve)  to  carbon  12  is  used  to  date  remains  of  living  things  

 

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Half  life  

Half life: 0

Half life: 1

Half life: 2

Linear

Exponential

• The half life is the amount of time needed for half the parent isotope to decay to the daughter isotope

By measuring how many half-lives have passed since rock was formed, age of rock is determined.

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The  Half-­‐life  of  14C  is  5,730  years.    

Using  radiometric  da/ng:  Oldest  Rocks  on  Earth  

•  Oldest rocks on Earth are the Acasta Gniess of northern Canada •  4030 million years old

© NASA

Acasta Gneiss

Zircon mineral