A. If we look at matter under ever greater magnification, we find that all matter consists of “collections of things that cannot be broken down any further by chemical means.” These are called atoms. A chemist named Dalton once defined an atom as the smallest unit of matter that could not be broken down any further.
Does that mean there is nothing smaller? Electrons, protons, and neutrons have since been discovered, disproving Dalton’s definition and theory. It is helpful to think of atoms as the basic units that make up matter.
An electrically neutral particle formed by multiple atoms joined by chemical bonds is called a molecule. Atoms also have properties of their own; they do not acquire chemical properties for the first time only when they form molecules.
For example, oxygen is a substance called O₂, formed when two atoms designated O come together (An individual oxygen atom, O, also has properties, such as reactivity, that differ from those of O₂). Rose fragrance is said to consist of 400 or more scent molecules (aroma compounds (in Japanese)).
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