The Physics
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Diameter of an Atom

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Bibliographic Entry Result
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Henry F. Holtzclaw & William R. Robinson. General Chemistry. Lexington, MA: Heath, 1988: 98. "The diameter of an atom is of the order of 10−8 cm." 0.1 nm
March, Robert H. Atom. USA: World Book Encyclopedia, 1995: 870. "The diameter of an atom ranges from about 0.1 to 0.5 nanometer." 0.1–0.5 nm
Metcalf, Williams, & Castka. Modern Chemistry. New York: Holt, Rinehart & Winston, 1980: 43. "The diameter of a nucleus is about 10−12 cm. This is about one ten-thousandth of the diameter of an atom itself, since atoms range from 1 × 10−8 to 5 × 10−8 cm in diameter." 0.1–0.5 nm
Speakman, J. C. Molecules. New York: McGraw-Hill, 1966: 19. "Atoms vary in size according to the element, but their diameters are of the order of 1 × 10−8 cm." 0.1 nm

An atom is one of the basic units of matter. Everything around us is made up of atoms. An atom is a million times smaller than the thickest human hair. The diameter of an atom ranges from about 0.1 to 0.5 nanometers (1 × 10−10 m to 5 × 10−10 m).

All the atoms of an element are not alike, however. For example, a second kind of hydrogen exits which is present in every sample of the gas no matter where it is obtained. It weighs twice as much as the more common hydrogen and is called deuterium or heavy hydrogen. The diameter of an atom for this type of hydrogen differs from the more common type.

Atoms vary greatly in weight, but they are all about the same size. For example, an atom of plutonium (one of the heaviest elements) weighs more than 200 times as much as a hydrogen atom (the lightest element), but the diameter of a plutonium atom is only about 3 times that of a hydrogen atom.

Michael P. -- 1996

Bibliographic Entry Result
(w/surrounding text)
Brown, LeMay, Bursten. Chemistry-The Central Science. New Jersey: Prentice Hall, 1997: 44. "Atoms are extremely small; most have diameters between 1 × 10−10 m and 5 × 10−10 m." 0.1–0.5 nm
The World book Encyclopedia. vol. 1 Chicago: World Book, 1996: 870. "The diameter of an atom ranges from about 0.1 to 0.5 nanometer." 0.1–0.5 nm
The World of Science: Chemistry in Everyday Life. vol. 14. Oxford: Equinox, 1989: 31. "Atom… name given to a relatively stable package of matter, typically about 0.1 nm across." 0.1 nm
Bixby, William. Great Experimenters.New York: David McKay, 1964: 150. "According to Rutherford, the radius of the entire atom was 0.00000001 cm." 0.1 nm
Baylis, William E. Macmillan Encyclopedia of Physics. New York: Prentice Hall, 1996: 71. "the Bohr radius ao = 5.2917725 × 10−11 m is the unit of length." 0.106 nm

An atom is one of the basic units of matter. Atoms form the building blocks of the simplest substances, the chemical elements. Nearly everything on earth is made up of atoms. Each element consists of one basic kind of atom. An atom is incredibly small -- more than a million times smaller than the thickness of a human hair. Tiny as atoms are, they consist of even more minute particles. The three basic types are protons, neutrons, and electrons. Protons have a positive electrical charge, and electrons have a negative charge. Neutrons are electrically neutral. The protons and neutrons are crowded into the nucleus, a tiny region at the center of the atom. The nucleus makes up nearly all the mass of an atom. The rest of the atom outside the nucleus is mostly empty space. The electrons whirl through this space. All atoms of the same element have the same number of protons. The atomic number tells how many protons an atom has.

The size of an atom is difficult to describe because atoms have no definite outer boundary. To overcome this problem, the size of an atom is estimated by describing its radius. In metals, this is done by measuring the distance between two nuclei in the solid state and dividing this distance by 2. For nonmetallic elements, that exist in pure form as molecules, measurements can be made of the distance between nuclei for two atoms covalently bonded together. The diameter of an atom ranges from 1 × 10−10 m to 5 × 10−10 m. There is no one definite diameter of an atom because since the number of electrons in the outer principal energy level increases as you go from left to right in each period, the corresponding increase in the nuclear charge due to the additional protons pulls the electrons more tightly around the nucleus. This attraction results in the radius to be generally reduced. For a group of elements in the periodic table, the atoms of each successive member have another outer principal energy level in the electron configuration that electrons can move to. The increased distance from the nucleus results in the atomic radius to increase in a group.

Judy Dong -- 1998