In this section, we delve into the versatile nature of carbon and its ability to form numerous bonds with other elements such as halogens, oxygen, nitrogen, and sulfur. This section highlights the importance of heteroatoms in replacing hydrogen in hydrocarbon chains while still satisfying carbon's tetravalency. Functional groups, which confer specific properties to compounds, are crucial to understanding organic chemistry. The concept of homologous series is introduced, where groups of compounds with similar structure but varying lengths show gradual changes in physical properties while maintaining similar chemical properties due to their functional groups. This versatility of carbon, with its property of catenation and tetravalency, underpins the multitude of organic compounds present in nature.