In chemistry 101 and 102 even at the High School level, one is introduced to the Chart of Elements. We learn about electrons, protons, neutrons and all those orbital shells.
Organic life, is based upon Carbon, Nitrogen, Oxygen, Helium, Phosphorous and a smigging of the other elements. It is what makes DNA and RNA nucleotide bases.
Alien life, could include Silicon, as a replacement for the Carbon.