why can metals conduct? and what is metallic bonding?
Metals do become brittle - depending on their thermal history. Generally speaking, the harder a metal is, the more brittle it is. Some examples of brittle metals: Iridium, Bismuth, and man made Plutonium (Pu). Similar to most substances, metals solidify as many separate crystals. The line where two or more crystals touch is called the grain boundary. If the grain boundary is weaker than the crystals themselves, then a crack can easily propagate through this boundary and fractures occur. If the metal is treated in such a way so that many multiple crystals form simultaneously (as when the metal is heated to an extremely high temperature and then cooled rapidly), then multiple, interconnected grain boundaries form and an impact with a high enough force can cause these boundaries to break apart making the metal appear to have shattered.
No, usually the transition metals (of which iron is classified as) demonstrate maleable and ductile qualities most characteristic of metals. Bismuth is a very brittle metal.
