Chemical nomenclature expresses the structure of compounds. Various nomenclature systems are used. Hence, a compound may have several acceptable names. Which name is preferred depends on the context. Each nomenclature type has several dialects due to different languages or other national variations. Even though the language of science communication is increasingly English, there are still differences such as aluminium versus aluminum and sulfur versus sulphur for the names of elements, icosane versus eicosane for the C₂₀ hydrocarbon chain, and but-2-ene versus 2-butene for the locant.