For predicting its chemical reactivity, generally you look at where it lies on the periodic table, which groups it with metals, semimetals, or nonmentals. Metals ...

To give provisional names to his predicted elements, Mendeleev used the prefixes eka-, dvi-, and tri-, ... Property, Ekaaluminium, Gallium ... chemically inert Group 0 elements could have gone undetected and be responsible for radioactivity.

Periodic Table (Predicting the Structure and Properties of the Elements) ... The number of neutrons added is unpredictable but can be determined from the total ...