Intro to Half-Life PhET Lab (Radioactive Dating Game).

Intro to Half-Life PhET Lab (Radioactive Dating Game).

Introduction: Dead things decay into simpler molecules.  Radioactive particles decay.  Is it the same kind of decay?  What does it mean when a substance is radioactive?  In this simulation, you will investigate the concept of half-life.

Some handy vocabulary for you to define:  (use your notes, your book, or the internet)

Neutron _______________________________________________________________________________________________

Isotope _______________________________________________________________________________________________

Radiocarbon Dating______________________________________________________________________________________

Half-Life _______________________________________________________________________________________________

Decay (as used in half-life)_________________________________________________________________________________

Carbon-14…what does the “14” represent? ___________________________________________________________________

Procedure: PhETàPlay with the Sims à Chemistry à Radioactive Dating Game

• Take some time and play with the simulation. Those atoms are radioactive!  How cool is that?!
• How many protons does Carbon-14 have? _____________ (hint…what is its atomic number?)
• How many neutrons does Carbon-14 have? _____________ (hint: what is the mass?)
• Add a Carbon-14 atom to the play area. What happens to that Carbon-14 atom? ________________________________________________________________________________
• Do all Carbon-14’s decay at the same time? ____________________________________________
• Add 50 Carbon-14s. (click  five times.)  What happens? _______________________________________________
• and Using 20 Carbon-14s, draw the pie graph at the following time periods:

• Redo the above with 100 Carbon-14 atoms and fill in the three boxes below.

• How do the pie graphs of 20 atoms compare to those of 100 atoms? __________________________________________
• Generally, does the size of a radioactive sample affect half-life? __________ Why/Why not? _______________________

Consider Uranium-238…

• Carbon-14’s half-life was measured in thousands (5700) of years. About how long is Uranian-238’s half-life? _________________________________________________________________________
• How many protons does U-238 have? _____________ How many neutrons? __________________
• Into what atom does Uranium-238 decay? ______________________________________________
• Does the size of the sample of Uranium-238 affect its half-life? _______________________________________________

About that Unknown Element….

• How would you determine the half-life of this unknown element? Write up a little plan here:

• Estimate the half-life of this element. _________ seconds.

Observe the decay curves ( % remaining vs time) for Carbon-14 and Uranium-238.  Sketch the decay curve for those isotopes here:

Determine how the little Geiger counter works in Measurement and Dating Game.   Estimate the age of each of the following objects in the list below:

Analysis questions

1. Why can’t we use Carbon-14 to date the rocks? ___________________________________________________________
2. Why couldn’t the fish fossil or dinosaur skull be dated with either C14 or U238? _________________________________

___________________________________________________________________________________________________

3. Could Carbon-14 be used to date a hammer suspected of being used in 3400BC? _________ __________Why/Why not? ___________________________________________________________________________________________________
4. The half-life of the unknown element was about _______ seconds.
5. Starting with 100 Carbon-14 atoms, how many would you expect to have after one half-life? _____ After three? ______
6. Make a small sketch of what a decay curve may look like for an unknown elementà
7. You happen upon an antiques store and the clerk claims that he has a belt that was once worn by Alexander the Great, around 350 BC. You radiocarbon date it and find the percent of carbon to be 75% remaining.  Could the belt be genuine?

How did you arrive at your answer?

Intro to Half-Life PhET Lab (Radioactive Dating Game).