Sorry about the low audio volume, still working out the kinks in this nightmare that is video conversions and editing.
Here I compare the reactivity of two alkali (group 1) metals, Lithium and Sodium. Generally, reactivity increases as you go down a group in the periodic table, so since sodium is directly under lithium it will be more reactive.
Lithium is the lightest metal, and has the atomic number 3. Sodium is directly below it, having an atomic number of 11. Both are very shiny when freshly cut, but will tarnish rapidly in air. Both are extremely soft and can be easily cut with a knife.
Interestingly, lithium is one of the very few materials that will react with nitrogen (N2) under standard conditions. This forms the black lithium nitride, Li3N, which is why my sample turned black unlike the sodium, which forms only the white hydroxide NaOH.
