In antiquity, many opined about "the elements" in combination. Around 2500 years ago, Leucippus and Democritus founded the idea of atoms. Perhaps everything, they opined, was composed of indivisible building blocks. In the late 1700s, hydrogen and oxygen were discovered. Circa 1804, John Dalton revived atomism to explain chemical behavior. Then in 1869, Mendeleev developed the periodic table: organizing the atoms.
The job that takes me out of the house every morning (and funds my board gaming hobby) is 'analytical chemist'. This means I spend my day running fancily named instruments and explaining to other people what the numbers or graphs they spit out mean. In order to understand this stuff myself, a pretty significant chunk of my life from college onwards has involved using or referencing a periodic table. Reciting the noble gases in order