This movie shows lithium reacting with water. We see that lithium is next to helium in the periodic table (it follows helium). Lithiums proximity to a noble gas provides a useful connection to its reactivity. In general those elements closes to the noble gases are amoung the most reactive. When the sample of lithium is dropped into the water we see a reaction occurs because bubbles are formed. We talked about these bubbles in class. We wondered what the gas was. The only substances initially are lithium and water. So the gas has to be something with the elements Li, H or O. We know both hydrogen and oxygen are gases. We do not know whether compounds containing lithium can be gases. (HINT: Anytime a metal reacts with another substance the compound produced which has the metal will not be in the gas phase.) So we can only conclude the gas is either hydrogen or oxygen. Turns out the gas is hydrogen. We'll learn later this semester how to tell whether the gas is hydrogen or oxygen by a simple experiment.