Many molecules, such as water, contain hydrogen. Pure hydrogen gas is explosive. It is used in balloons because it is very light and, unlike hydrogen, it is not explosive. Lithium is the lightest metal but is too active to be used in its pure form. It is used in watch batteries.
Beryllium is in beryl gems such as emeralds and aquamarines.
Boron is used in heat-resistant glassware. Carbon is the basis of life. A single carbon atom can combine with up to four other atoms, so it can make the many complex molecules needed by living things. It is also in products made from plants and animals, such as wood, cloth, and plastic. Pure carbon can be the soft graphite in pencils, or diamond, the hardest element.