This applet models the packing of anions (A, blue) and cations (B, orange) in ionic crystals of a tetrahedral arrangement (4-coordinate). By comparison with the Crystal Packing (Square Planar) Applet, you will notice that certain radius ratios favor tetrahedral arrangement, and others favor square planar.
The cation is at the center of the tetrahedron, and the anions are located at the vertices, though only two of the four anions present are displayed for the sake of clarity.
Click on r+ to increase the radius of the cation, and r- to reduce the radius. The radii of the anions are automatically adjusted, subject to the restraint that two ions can not impinge on each other's space.
The radii of the cation and the anions is displayed in numerical form on the right side of the applet. The ratio of the radius of A to the radius of B is calculated and displayed. Notice that for certain ratios, the space inside the crystal unit cell is used most efficiently. The packing ratio (ratio of the used space to the available space in the unit cell) is calculated and displayed.
© 2004-2011 by Lawrence T. Sein. All rights reserved.
Send questions to: lseinjr@hotmail.com