Ionic bonding between sodium and chlorine atoms. Electron transfer from Na to Cl creates a cation (Na ) and an anion (Cl-). The ionic bond is due to the coulombic attraction between the ions of opposite charge.

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Ionic bonding between sodium and chlorine atoms.
Electron transfer from Na to Cl creates a cation
(Na) and an anion (Cl-). The ionic bond is due
to the coulombic attraction between the ions of
opposite charge.
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Regular stacking of Na and Cl- ions in solid
NaCl, which is indicative of the nondirectional
nature ofionic bonding.
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The covalent bond in a molecule of chlorine gas,
Cl2, is illustrated with (a) a planetary model
comparedwith (b) the actual electron density,
(c) an electron-dot schematic, and (d) a bondline
schematic.
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(a) An ethylene molecule (C2H4) is compared with
(b) a polyethylene molecule that
results from the conversion of the CC double
bond into two CC single bonds.


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Two-dimensional schematic representation of the
spaghetti-like structure of solid polyethylene.
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Metallic bond consisting of an electron cloud, or
gas. An imaginary slice is shown through the
front face of the crystal structure of copper,
revealing Cu2 ion cores bonded by the
delocalized valence electrons.
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Hydrogen bridge. This secondary bond is formed
between two permanent dipoles in adjacent water
molecules. (From W. G. Moffatt, G. W. Pearsall,
and J. Wulff, The Structure and Properties of
Materials, Vol. 1 Structures, John Wiley Sons,
Inc., New York, 1964.)
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TABLE 3.1 (CONTINUED)
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The simple cubic lattice becomes the simple cubic
crystal structure when an atom is placed on each
lattice point.
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Body-centered cubic (bcc) structure for metals
showing (a) the arrangement of lattice points for
a unit cell, (b) the actual packing of atoms
(represented as hard spheres) within the unit
cell, and (c) the repeating bcc structure,
equivalent to many adjacent unit cells. Part (c)
courtesy of Accelrys, Inc.
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Face-centered cubic (fcc) structure for metals
showing (a) the arrangement of lattice points for
a unit cell,(b) the actual packing of atoms
within the unit cell, and (c) the repeating fcc
structure, equivalent to many adjacent unit
cells. Part (c) courtesy of Accelrys, Inc.
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Hexagonal close-packed (hcp) structure for metals
showing (a) the arrangement of atom centers
relative to lattice points for a unit cell. There
are two atoms per lattice point (note the
outlined example). (b) The actual packing of
atoms within the unit cell. Note that the atom in
the midplane extends beyond the unit-cell
boundaries. (c) The repeating hcp structure,
equivalent to many adjacent unit cells. Part (c)
courtesy of Accelrys, Inc.
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Comparison of the fcc and hcp structures. They
are each efficient stackings of close-packed
planes. The difference between the two structures
is the different stacking sequences. (From B. D.
Cullity and S. R. Stock, Elements of X-Ray
Diffraction, 3rd ed., Prentice Hall, Upper Saddle
River, NJ, 2001.)
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Sodium chloride (NaCl) structure showing (a) ion
positions in a unit cell, (b) full-size ions, and
(c) many adjacent unit cells. Parts (b) and (c)
courtesy of Accelrys, Inc.
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Fluorite (CaF2) unit cell showing (a) ion
positions and (b) full-size ions. Part (b)
courtesy of Accelrys, Inc.
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Many crystallographic forms of SiO2 are stable as
they are heated from room temperature to melting
temperature. Each form represents a different way
to connect adjacent tetrahedra.
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(a) C60 molecule, or buckyball. (b) Cylindrical
array of hexagonal rings of carbon atoms, or
buckytube. (Courtesy of Accelrys, Inc.)
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Arrangement of polymeric chains in the unit cell
of polyethylene. The dark spheres are carbon
atoms, and the light spheres are hydrogen atoms.
The unit-cell dimensions are 0.255 nm 0.494 nm
0.741 nm. (Courtesy of Accelrys, Inc.)