This image is a model of an atom
Windows to the Universe original animation by Randy Russell.
What's a molecule?
A Matter of Scale - interactive showing the sizes of things, from very tiny to huge - from NSF
Atoms are the smallest size pieces that elements come in. Each atom has a small but heavy nucleus at its center. A cloud of tiny, fast-moving electrons orbit around the nucleus. The nucleus contains at least one proton. The nucleus usually also has neutrons. Most of the time there are about as many neutrons as protons. A "normal" atom that doesn't have an electrical charge has the same number of electrons (which have negative electrical charges) and protons (which have a positive charge).
The animation of an atom on this page is NOT to scale. The distance between the nucleus and the electrons in an actual atom are much larger in comparison with the sizes of the protons, neutrons, and electrons. Most of an atom is empty space. Atoms are incredibly small. They range in size from about 60 to 500 picometers (a picometer is 10-12 meters, or one trillionth of a meter). The nucleus of an atom is about 100,000 times smaller than the whole atom. Almost all (more than 99%) of the mass of an atom is in the nucleus.
Sometimes two or more atoms "stick together" to form a molecule. Some molecules have atoms of just one type. For example, an oxygen molecule (O2) has two oxygen atoms. Other molecules combine different types of atoms. Methane (CH4) has one carbon atom and four hydrogen atoms.
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