A03    Identify the three types of primary bonds, and explain the differences among these three types regarding bond strength, bond direction, and ability to reestablish a broken bond.

The three types of primary bonds are: covalent, ionic and metallic bonds. Of these bonds, the covalent and ionic bonds are the strongest.  Covalent bonds have very precise bond directions and ionic bonds are based on direct electrostatic interaction between ions. Metallic bonds are the weakest but also the ones that can most easily reform. The reason is that their outer electrons are shared by all positive core structures. Shortly, metals can be described as consisting of positive ions surrounded by a gas of electrons. The latter explains why metals conduct electricity and heat, but also their ability to deform plastically. The latter relates to slippage between the positive ions and a redistribution of the electron gas.

From the above drawings we can visualize what happens if a layer of any of the above materials is displaced a distance corresponding to the diameter of an atom. In the case of the ionic material, equal charge types will become nearest neighbors, causing the two layers to repel each others. In the case of the covalent bonds, the likelihood of reforming bonds is not high because of the rather precise bond directions of covalent bonds. However, in the case of the metal, the electron gas will regroup and reestablish bonding between the two layers.

From the above we can understand why materials that use only ionic and/or   covalent bonds are brittle (they cannot easily reform bonds during displacements), while it is rather easy to reshape metals because of their plastic deformation ability (caused by slippage occurring between atomic planes).