By mass, about 96 percent of our bodies are made of four key elements: oxygen (65 percent), carbon (18.5 percent), hydrogen (9.5 percent) and nitrogen (3.3 percent). ▶ O (Oxygen) - 1 mole = 15.999 g; 1 gr. = 37.5 sextillion atoms. ▶ C (Carbon) - 1 mole = 12.011 g. This means that 1 gram of carbon consists of 50 sextillion atoms. ▶ H (Hydrogen) - 1 mole = 1.008 grams of hydrogen. This means that one gram of hydrogen consists of 6,022 x 10^23 atoms, or 595 sextillion (595 trillion times billion