View the full answer. The key difference between element and molecule is that elements are pure substances that consist of only a single type of atom and cannot be broken down by chemical means while molecules may contain two or more atoms of the same element or different elements. Differences Between Elements Compounds Mixtures Compounds And Mixtures Elements Compounds And Mixtures Compounds Science Define the terms element and compound and name the smallest unit of each. . H2O is molecules of compound. The difference between mineral and element is that a mineral is a naturally occurring inorganic compound that we can breaks down into simpler structure via chemical processes whereas an element is a substance that cannot be converted into further simpler structures via any ordinary chemical process. A compound on the other hand consists of atoms of different elements and is chemically combined in a fixed ratio. A from liqu...