Radioactive decay slows down as sample size decreases. The decay slows in such a way that the amount of time it takes for half the radioactive sample to decay is constant regardless of the size of the sample. The time it takes for half of a radioactive sample to decay is called the half life. This PowerPoint presentation explains why the rate of decay diminishes as sample size decreases. It explains what half life is, and shows two approaches to doing quantitative problems relating to half life. It also explains the process of radioactive dating. Worksheets on this topic are available free of charge on my website at www.evanschemistrycorner.com.