3 characteristics of the carbon atom that makes possible the building of variety of biological molecules are:
• Carbon atoms can easily form covalent bonds with nitrogen, hydrogen, oxygen, sulfur and with carbon. The bonds can be single, double or triple between the atoms. This combination of carbon with other elements and with itself results in the formation of huge number of biological molecules.
• The size of carbon atom is very small in comparison to most other atoms. Thus, the bond formed between two carbon atoms is quite short. And the shorter bonds are more stronger than the longer bonds between two atoms, that's why carbon bonds are stable at the different temperatures associated with life.
• Only carbon can form stable four covalent bonds with the other elements, which makes it versatile element to serve as the basic structural component, of the macro-molecules.
