Isotopes are atoms of the same element that have a different number of neutrons. Carbon exists as three main isotopes: Carbon-12, Carbon-13, and Carbon-14. Carbon-14 is unstable because it has more neutrons than protons, causing radioactive decay over time. The half-life of an isotope is the amount of time it takes for half of its atoms to decay, and can be used to determine the age of fossils that contain Carbon-14. An activity using M&M candies demonstrates radioactive decay and half-life by having students count the number of candies after simulated periods of decay.

1. Chemistry: Isotopes

2. Review on atoms from yesterday: Each element is made of atoms E.g. Oxygen is made of oxygen atoms, gold is made of gold atoms Atoms have a specific atomic number and atomic mass Atomic # = # protons # protons = # electrons Atomic mass – Atomic # = # neutrons (USUALLY!)

3. ISOTOPES Isotopes are atoms of the same element with a different number of neutrons Most atoms of carbon have 6 protons and 6 neutrons BUT some atoms of carbon have 7 neutrons or 8 neutrons These other kind of carbon atoms are called isotopes.

4. These isotopes of carbon are called: (pg. 47) Carbon-12 Carbon-13 Carbon-14 These atoms are unstable because the number of protons does not equal the number of neutrons The protons start to repel and release particles to become stable, called radioactive decay

5. Half - Life We can measure decay by studying half-life Half-life = time for half of the atoms in an element to decay For example, if you start with 10g of carbon-14, after 2 weeks you may have only 5g left. Carbon-14 may be used to examine the age of fossils!

6. M&Mium activity Each M&M represents one atom of the mysterious element M&Mium. Count the number of M&Miums you are starting with. Record this number on a piece of paper. Shake the M&Miums in your cup and dump them out CAREFULLY onto a clean sheet of paper. Don’t lose any of them! Any M&Miums that have the “M” facing up are radioactive! 5) The ones that are blank have decayed to Blankium. 6) Remove the Blankium M&Ms and count the remaining M&Miums. 7) Shake again, and repeat removing the Blankiums until there are no more M&Miums left! Make sure to record the number of times you shake, too! 8) GRAPH the data! Y-axis = Number of M&MiumsX-axis = Number of shakes (number of half-lives)

7. 5) The ones that are blank have decayed to Blankium. 6) Remove the Blankium M&Ms and count the remaining M&Miums. 7) Shake again, and repeat removing the Blankiums until there are no more M&Miums left! Make sure to record the number of times you shake, too! 8) GRAPH the data! Y-axis = Number of M&MiumsX-axis = Number of shakes (number of half-lives)