10.4 Structure and Bonding In Metals How do metals arrange themselves?

A. Closest Packing Structure Arrangement of packing uniform hard spheres into the most efficient use of available space to the component parts Spheres are arranged in layers, with each sphere being surrounded by six others In the second layer, the spheres do not lie directly on top of each other but instead fill in dimples formed by three spheres in the first layer In the third layer the particles can arrange themselves in two ways: They can lay directly over the spheres in layer #1 (a, b, a, arrangement) Or they can occupy spots so no sphere in layer 3 sits on top of a sphere from layer 1 (abc arrangement)

B. Hexagonal Closest Packing (aba,) packing Has a hexagonal unit cell structure Each layer is identical to the layer below it The spheres in every other level occupy the same vertical position (hence aba arrangement) Sometimes abbreviated as hcp packing

Cubic Closest Packed Structure (abc, abc) arrangement of particles in the structure Has a face centered cubic unit cell Referred to as a cubic closest packed structure (ccp) The spheres in every 4th layer occupy the same vertical position hence (abc, abc) arrangement

What is common to both structure types? Each sphere has 12 equivalent nearest neighbors 6 are in the same layer 3 are in the layer above 3 are in the layer below If we know the net number of spheres, we can use this information to figure out the empirical formula of the compound, and can make predictions with regards to physical/chemical behavior

Bonding Models for Metals 10.4 Continued

Electron Sea Model See Notes

Metal Alloys Alloys are substances that contain a mixture of elements and have metallic properties Two types of alloys exist

Substitutional Alloys Alloy where the host metal atoms are replaced by other metal atoms of similar size Ex: Brass

Interstitial Alloy Formed when some of the holes in the closest packed structure of the metal have been filled in with smaller atoms Steel is the best example of this, where carbon atoms (smaller) fill in some of the holes in the iron (larger) closest packed structure By adding the smaller atoms, you alter properties of the host metal