Final answer:
Chemical reactivity is determined by the number and spatial distribution of an atom's electrons. The periodic table groups elements based on their chemical properties, which are influenced by the number of reactive electrons. Reactivity can be predicted based on the group number and the number of valence electrons.
Step-by-step explanation:
Chemical reactivity is determined by the number and spatial distribution of an atom's electrons. The periodic table groups elements according to their chemical properties, which are influenced by the number of reactive electrons. Elements in the same group have similar chemical properties because they have the same number of valence electrons. For example, all elements in Group 1 have one valence electron and tend to react with other elements to lose that electron and achieve a stable electron configuration. On the periodic table, chemical reactivity can be predicted by the group number and is correlated with the number of valence electrons.