What are compounds that have the same mass and elements but different structural alignments called?

Compounds that have the same mass and elements but different structural alignments are known as isomers. Isomers are characterized by having the same molecular formula, meaning they contain the same number and types of atoms; however, they differ in how these atoms are arranged in space. This structural variation can significantly affect their chemical properties and behavior.

For example, the simplest form of isomerism is structural isomerism, where the connectivity of atoms differs. Isomers can also include stereoisomers, where the arrangement of atoms in three-dimensional space varies, leading to different spatial configurations. The diverse arrangements contribute to the unique characteristics of each isomer, making them an essential concept in chemistry.

Other terms, such as allotropes, refer to different forms of the same element, enantiomers refer to chiral molecules that are mirror images of each other, and homologues typically describe compounds that follow a specific structural pattern, usually in a series that differ by a repeating unit. These concepts, while important, do not define the relationship described in the question regarding different structural alignments of compounds with the same mass and elements.