Noble gases already have 8 valence electrons, which means their outermost energy level is completely filled. It doesn't need other elements to react with it. The noble gases are in the last group of the periodic table. Group 1, alkali meatballs, are the most reactive since they carry only 1 valence electrons and need to react with other elements
Every substance is either an element or a compound. There is ionic compounds, molecular compounds, but they are all considered compounds. Hope I helped.
