In this paper I consider the structures that chemists and physicists attribute at the molecular scale to substances and materials of various kinds, and how they relate to structures and processes at other scales. I argue that the structure of a substance is the set of properties and relations which are preserved across all the conditions in which it can be said to exist. In short, structure is abstraction. On the basis of this view, and using concrete examples, I argue that structures, and therefore the chemical substances and other materials to which they are essential, are emergent. Firstly, structures themselves are scale-dependent because they can only exist within certain physical conditions, and a single substance may have different structures at different scales (of length, time and energy). Secondly, the distinctness of both substances and structures is a scale-dependent relationship: above a certain point, two distinct possibilities may become one. Thirdly, the necessary conditions for composition, for both substances and molecular species, are scale-dependent. To know whether a group of nuclei and electrons form a molecule it is not enough to consider energy alone: one also has to know about their environment and the lifetime over which the group robustly hangs together.

在本文中，我考虑了化学家和物理学家在分子尺度上归因于各种物质和材料的结构，以及它们与其他尺度上的结构和过程的关系。我认为物质的结构是一组属性和关系，它们在可以说它存在的所有条件下都保持不变。简而言之，结构就是抽象。基于这种观点，并使用具体的例子，我认为结构，以及它们所必需的化学物质和其他材料，都是涌现的。首先，结构本身是尺度相关的，因为它们只能存在于特定的物理条件下，单一物质在不同的尺度（长度、时间和能量）上可能具有不同的结构。其次，物质和结构的独特性是一种尺度相关的关系：在某一点之上，两种不同的可能性可能会合二为一。第三，对于物质和分子种类而言，组成的必要条件都取决于尺度。要知道一组原子核和电子是否形成一个分子，仅考虑能量是不够的：还必须了解它们的环境以及该组牢固地结合在一起的寿命。