Group 1 is the first column of the periodic table they are the alkali metals. They all share common traits. They all react with water and air some explosively. For instance putting caesium in water can blow a hole in a submarine with the force of a depth charge.
Group 7 elements are non metals that decrease in reactivity down there group. Fluoride is at the top of the group and if combined with hydrogen will also explode.
Group 8 or 0 or the noble gases are non metals. They are boring and unreactive however that gives them a lot of practical uses that don't end in explosions.
Using the trends and patterns across groups and periods (horizontal rows) new element places can be predicted for the future. Therefore the periodic table, although over a century old, still isn't finished. Ununseptium is the most recent discovery and fell perfectly into its place for its properties