The main terminal element in organic molecules is carbon. Carbon is fundamental to life on Earth and is the basic building block of organic chemistry. It has four valence electrons, allowing it to form stable bonds with various elements, including hydrogen, oxygen, nitrogen, and others. This versatility enables the formation of complex molecules like carbohydrates, lipids, proteins, and nucleic acids, which are essential for life's processes. Carbon's unique bonding properties facilitate the creation of long chains and rings, making it possible for a diverse range of organic compounds.