-+Bonding+in+Metals

toc =- metallic bonds=

=- body-centered cubic structure=

Body-Centered Cubic Structure:



The structure is very compact and arranged in an orderly pattern with ** 8 neighbors **. The centers of the atoms (or spheres) are used to represent the corners of the unit cell, and 8 unit cells share each of these atoms. There is a whole atom located in the center of the unit cell. Examples: Li, Na, K, Rb, Ba, V, Cr and Fe (at room temperature).

=- face-centered cubic structure=

Face-Centered Cubic Sturucture Also knows as close-packed or CCP



Elements with this Structure: Al, Cu, Ni, Sr, Rh, Pd, Ag, Ce, Tb, Ir, Pt, Au, Pb, Th

The Face (or Head)-Centered Cubic Structure has 12 neighboring electrons -Atoms are arranged at the corners and center of each cube face of the cell. Atoms are assumed to touch along face diagonals -The lattice parameter, a, is related to the radius of the atom in the cell through: -Coordination number: the number of nearest neighbors to any atom. For FCC systems, the coordination number is 12.

=- hexagonal close-packed structure=

**Hexagonal Close Packed (HPC) Structure** Another common close packed structure is the hexagonal close pack. The hexagonal structure of alternating layers is shifted so its atoms are aligned to the gaps of the preceding layer. The atoms from one layer nest themselves in the empty space between the atoms of the adjacent layer just like in the fcc structure. However, instead of being a cubic structure, the pattern is hexagonal. (See image below.) The difference between the HPC and FCC structure is discussed later in this section.



=- alloys=

An alloy is a mixture composed of two or more elements. Alloys can revert to a previous state when heated or when the stress that caused their shape is removed. This ability is due to the alloy having two possible crystal structures.

Alloys are often made in order to alter the mechanical properties of the base metal, to induce hardness, toughness, ductility or other desired properties. While most metals and alloys can be work hardened inducing defects in their crystal structure, caused byplastic deformation some alloys can also have their properties altered by heat treatment Many alloys of copper, magnesium titanium, and nickel can be strengthened to some degree by some method of heat treatment, but few respond to this to the same degree that steel does. Alloys contain atoms of different sizes, which distort the regular arrangements of atoms. This makes it more difficult for the layers to slide over each other, so alloys are harder thanthe pure metal.