Liquids and solids are two fundamental states of matter. However, our understanding of their three-dimensional atomic structure is mostly based on physical models. Here we use atomic electron tomography to experimentally determine the three-dimensional atomic positions of monatomic amorphous solids, namely a Ta thin film and two Pd nanoparticles. We observe that pentagonal bipyramids are the most abundant atomic motifs in these amorphous materials. Instead of forming icosahedra, the majority of pentagonal bipyramids arrange into pentagonal bipyramid networks with medium-range order. Molecular dynamics simulations further reveal that pentagonal bipyramid networks are prevalent in monatomic metallic liquids, which rapidly grow in size and form more icosahedra during the quench from the liquid to the glass state. These results expand our understanding of the atomic structures of amorphous solids and will encourage future studies on amorphous–crystalline phase and glass transitions in non-crystalline materials with three-dimensional atomic resolution.

液体和固体是物质的两种基本状态。然而，我们对它们的三维原子结构的理解主要是基于物理模型。在这里，我们使用原子电子断层扫描来实验确定单原子无定形固体的三维原子位置，即一个 Ta 薄膜和两个 Pd 纳米颗粒。我们观察到五边形双锥体是这些无定形材料中最丰富的原子基序。大多数五角双锥不是形成二十面体，而是排列成具有中等顺序的五角双锥网络。分子动力学模拟进一步表明，五角双锥网络在单原子金属液体中普遍存在，在从液体到玻璃状态的骤冷过程中，其尺寸迅速增长并形成更多的二十面体。