Ozone, made of three bonded oxygen atoms, is found 15-30 km above Earth, has a strong smell, is blue, and blocks sunlight from hitting the surface of Earth. The 22nd lesson in a series of 36 specifically focuses on the important elements and their compounds from groups 16, 17, and 18 on the periodic table. It explores oxygen, sulfur, fluorine, chlorine, and compounds of noble gases. Classes learn their structures, discuss their preparation, and can explain their different uses in our lives.