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 People realized that atoms exists surely. Then they questioned what the size of an atom is. According to various experiments, Avogadro's constant has turned out to be Since a solid like a metal block is tightly filled with atoms as shown in the following figure, we can easily estimate the size of the atom. Suppose the radius of atom to be r cm. Then atoms would line up in 1 cm and atoms occupy the volume of Suppose the density of the metal to be Let the molecular weight of the metal, which is equal to the atomic weight in the case of metal, be A. The volume of 1 mol of the metal is . Therefore the volume occupied by one atom of the metal is obtained by dividing by Avogadro's constant NA. Namely, Accordingly, the radius of the atom is considered to be For example, the radii of some solid-state atoms estimated by using the above formula are listed in the following Table. From these results, we can presume that the size of an atom is approximately several angstroms (1 angstrom = 10-8 cm = 10-10 m).
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