The periodic table enabled elements to be classified. Group 1 elements, Lithium, Sodium, Potassium etc are highly reactive. Group 8 (now group 18) elements are noble gasses, Helium, Neon, Argon etc which are very unreactive.
There are also the transition elements which are usually metals.
The periodic table works well for lighter elements. Heavier elements don't fit the pattern too well due to electron configurations.
Gold is a good example. It has a single outer s shell electron. It should be highly reactive like Potassium. Quite the opposite it is highly unreactive, The reason being that the full underlying d shell electrons hide it.
The newly discovered group 18 element Oganesson atomic number 118 is predicted to behave more like a metal than a noble gas.