Metallic Bonding

A.  Key Information

1.  A metallic bond occurs when positive metal ions like Cu⁺² or Fe⁺³ are surrounded by a "sea of electrons" or freely-moving valence electrons.  The valence electrons are not bound to any particular cation, but are free to move throughout the metallic crystal.  In the picture below, the red circles are metal cations packed in a crystal lattice.  The black dots represent the "sea" of freely moving valence electrons.   (Note:  Metallic bonding is best understood with the "Band Theory of Molecular Orbitals, but we won't study this theory in our course.")

2.  The model of metallic bonding explains three properties of metals.

    A.  Metals are good conductors of electricity:  electric current is a movement of free electrons

    B.  Metals are ductile:  They can be drawn into wires because electrons are mobile.

    C.  Metals are malleable:  They can be hammered into sheets due to mobility of electrons.

3.  Metals, like ionic compounds, are crystalline solids. 

B.  Alloys

1.  Alloys are metallic substances composed of two or more elements- at least one of these elements is a metal.

2.  Alloys are important because the properties of an alloy are often superior to those of its component elements.

3.  Common alloys are:

   a.  Stainless steel (composed of iron, chromium, carbon and nickel)

   b.  Sterling silver    (composed of silver and copper)

   c.  14 karat gold    (composed of gold and copper:  Note:  Pure gold is too soft to wear as jewelry!)

   d.  Brass/bronze  (composed of copper and zinc)