Halogenation is a chemical reaction where a halogen atom, such as chlorine, bromine, fluorine, or iodine, is added to a molecule. This process often occurs in organic compounds, where halogens replace hydrogen atoms. For example, when ethane reacts with chlorine in the presence of light, it can form chloroethane and hydrochloric acid. This reaction is important in creating various chemical products, including pesticides and pharmaceuticals. Halogenation can change the properties of a compound, making it more reactive or altering its physical characteristics. Understanding this process helps chemists design new materials and improve existing ones.