Sodium reacting with water. After the movie has played drag the scroll bar to the beginning of the movie. Use the right arrow key to advance the movie two or three frames. Look at the shape of the sodium chunk in the water. Does it look round? now let the movie play again. Notice the chunk of sodium quickly becomes a sphere. This is because the sharp edges and corners react quickly and the spherical shape is formed. Watch as the sodium skims over the water reacting. As it reacts it gets smaller and smaller, until it disappears. The formation of the hydrogen gas bubbles is evident at the beginning of the reaction, but as the sodium gets smaller the bubbles are more difficult to see.