The sixth element in the periodic table, carbon, has the electron configuration 1
2 and, thus, has four valence electrons in the unfilled orbitals of its second electron shell. To fill these orbitals to a stable set of eight valence electrons, a single carbon atom may share electrons with two, three, or even four other atoms. No other element forms such strong bonds to as many other atoms as carbon does. Moreover, multiple carbon atoms readily link together with single, double, or triple bonds. These factors make element number 6 unique in the entire periodic table. The number of carbon‐based compounds is many times greater than the total of all compounds lacking carbon.
All types of life are based on carbon compounds, so the study of the chemistry of carbon is called organic chemistry. You should realize, however, that organic compounds are not necessarily derived from plants and animals. Hundreds of thousands of them have been synthesized (built) in the laboratory from simpler substances.
Figure 1 is an illustration of propane, one of the simplest organic compounds:
Figure 1. The structural formula of propane.