A Conclusion

A Summary of Bond Types

This brings to a conclusion the description of bonding. Three types of bonds - metallic, ionic and covalent - each have their own characteristics.

Metallic bonds are formed by pooled valence electrons of metallic atoms providing the negative charges to hold positively charged metallic ions together. This bonding structure provides for relatively low melting points and easy reshaping (bending, flattening). The delocalised electrons provide high electrical conductivity.

Ionic bonds are formed when metallic atoms donate valence electrons to non-metallic atoms. The resulting ions have opposite charges and attract each other into rigid lattices. This bonding structure gives high bond strength that provides brittle substances with high melting points and low conductivity. If the lattice is disrupted by being heated or dissolved in water, the ions break apart and find movement easier. Conductivity of molten or aqueous ions is much higher than that of solids.

Covalent bonds are formed when two non-metallic atoms approach and share valence electrons. These are the strongest of all bonds. Covalent networks form when atoms bond each to several others, making an interlocking web of atoms. Covalent networks are very hard to disrupt, giving these substances very high melting points and low conductivity in any state. Molecules form when a few covalent bonds form between a countable number of molecules, as in CO₂ or H₂O. While the bonds within the molecule are very strong, the molecules are so small that we commonly deal with a very large number of them. One molecule requires little energy to separate from another, so these substances have very low melting points, often below room temperature. Most liquids and gases that we are familiar with are molecular. Because molecules hold their electrons so tightly, molecules also tend to be poor conductors.