Praxis Elementary Education: Three-Subject Bundle – Science (5905) Practice Test

When atoms bond, they form a molecule—the smallest unit made of two or more atoms held together by chemical bonds. This term covers any bonded cluster, whether the atoms are the same element or different elements. If the bonded atoms are different elements, that molecule is a compound (like water, H2O). If the bonded atoms are the same element, it’s a molecular form of that element (like O2). A mixture is a physical combination of substances that aren’t bonded together, and an element is a pure substance made of only one kind of atom. So the small bonded units described are molecules.