Final answer:
An element’s reactivity is primarily determined by its electronegativity, first ionization energy, and atomic size, with highly reactive metals located in the lower left portion of the periodic table.
Step-by-step explanation:
The characteristics that determine an element’s reactivity are primarily electronegativity and first ionization energy. Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons, while ionization energy is the energy required to remove an electron from an atom or ion. The atomic size (or radius) also plays a significant role in reactivity, as it affects the ability of an element’s nucleus to attract and hold on to electrons. In the context of the periodic table, metallic character influences reactivity, with highly reactive metals located in the lower left portion and increasing reactivity as atomic size increases and as we move down a group.