1. Atoms and Isotopes IDS 102

2. What are atoms made of?  Protons  Lots of mass  Positive electric charge  Neutrons  Roughly same mass as proton (a little more)  No electric charge  Electrons  Not much mass  Most of the volume of the atom!  Negative electric charge

3. What determines the type of atom?  Atoms can easily gain or lose electrons (they become ions)  Protons and neutrons are tightly held  Protons & neutrons determine the mass  PROTONS determine the type of atom!  One proton? That’s hydrogen.  Six protons? That’s carbon.  Eight protons? That’s oxygen

4. Looking at hydrogen  Atomic mass is “1.008”  Most hydrogen has one proton and no neutrons.  Some has one proton and one neutron (that’s called dueterium and it is stable)  Some has one proton and two neutrons (that’s called tritium and it decays)

5. Tritium “decay”  It starts out as one proton, two neutrons and one electron.  When it “decays” one neutron turns into a proton and an electron.  This gives us an atom with two protons, one neutron, and two electrons  The new atom is called “Helium-3” and it is stable (unusual, but stable)

6. Do all tritium atoms decay at the same time?  No  On average, we expect a tritium atom to decay in about 12 years.  Some will decay sooner and some will decay later!!!  About a quarter will still be around in 24 years.