Timeline of the history of elements

Only 15 elements were know before modern times. It's a short list.

Ancient times there were a whole lot of competing theories about what makes up stuff. Classical elements of fire, earth, wind, water + other, were slightly more complicated that just those words. Atomism was the idea that everything could be divided smaller and smaller into discrete but unknown particles; versus substance theory that things when divided were just smaller versions of themselves.

That was just enough philosophy to explain metals. You can take some "earth" and divide it (by smelting, etc) until you get to an undivisible particle. That's how we get gold, copper, iron, tin, etc. It was really obvious that a person could manipulate something to get a pure form of something without needing to invoke ghosts or the void or phlogisten.

The general idea is something is an elementary particle until proven otherwise. Lots of missteps and bad guesses along the way.

There was a really weird short lived theory called tria prima that every substance was composed of three elements: a combustible element, a fluid and changeable element, and a solid, permanent element. That was a weird side tangent for explaining how smelting could make a pure element, by burning off the combustible and mixing with the correct flux to remove the fluid. But we still have the idea that there are unique particles of matter.

It was ~1730 that scientists started to get serious about observing the world. Antoine Laviosier proposed the new term of element to describe the basic undivisible particles we know and love today.

The killer discovery for finding elements was electrochemistry. It allowed someone to very carefully divide elements from each other, so long as you could dissolve the material and separate/capture what come off it.

My favourite is aluminium. It was predicted in 1756 because someone could see it was an oxide of something, but it wasn't isolated until 1824. In this example, a person found a new "earth" very early on, any every new it had to be smelted to isolate the atom inside. It just took a really really really long time to figure out how to dissolve it, such that electrolysis could remove the oxide or "earth" bits.