While metals are highly regarded because of their unique qualities, they are also,
generally, not useful in their pure forms. The very qualities that make them
unique can also make them useless. They are too soft and malleable. So, much
effort has been put into finding ways to keep the basic metallic qualities, but
modify them so that they are not so extreme.

  • The introduction of a non-metallic element into a metal will cut
    down on malleability and ductility. Why?
Anything which diminishes the electron sea will reduce malleability and ductility.  
This process is used on 'carbon hardened' knives to give them stronger and hold
a sharper edge.

  • The introduction of a non-metallic element into a metal will cut
    down on electrical conductivity. Why?
Anything which diminishes the electron sea will inhibit the easy flow of electrons.

    The introduction of a non-metallic element into a metal will cut
    down on thermal conductivity. Why?
    Anything which introduces rigid bonding into the metal will restrict the
    ability of the kernels to vibrate. With this loss of vibration, the system will not
    be readily able to conduct heat.
Metallic Bonds  - Mixing in Non-Metals