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.

Regular stacking of Na+ and Cl− ions in solid NaCl, which is indicative of the nondirectional nature ofionic bonding.

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.

(a) An ethylene molecule (C2H4) is compared with (b) a polyethylene molecule that results from the conversion of the C=C double bond into two C–C single bonds.

Two-dimensional schematic representation of the “spaghetti-like” structure of solid polyethylene.

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.

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.)

TABLE 3.1 (CONTINUED)

The simple cubic lattice becomes the simple cubic crystal structure when an atom is placed on each lattice point.

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.]

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.]

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.]

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.)

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.]

Fluorite (CaF2) unit cell showing (a) ion positions and (b) full-size ions. [Part (b) courtesy of Accelrys, Inc.]

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.

(a) C60 molecule, or buckyball. (b) Cylindrical array of hexagonal rings of carbon atoms, or buckytube. (Courtesy of Accelrys, Inc.)

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.)