4 / 14 Structure & Bonding

Stone, bronze, iron. Stone Age, Bronze Age, Iron Age... Plastic Age. Progress of civilization is characterized half by the amount of energy they can access and half by the material they can access. In this chapter we will look at how "stuff" differs in properties and why these differences exist.

We progress in several stages.

1. If we only have a chemical formula, how do we know which kind of bonding we can expect?
2. What are the microscopic characteristics of each kind of bond, and how does this govern the macroscopic properties? We will answer these two questions for each of the three major kind of bonds.
3. While all ionic compounds are similar to one another, and likewise with metallic compounds, molecules formed from covalent bonds are the most interesting. Their properties can be completely different from one another, and we need to look at why that is so.

Classifying Types of Chemical Bonds

A bond is the relationship that exist between two atoms. There are three kinds of bonds that could exist between them:

• Ionic bonding where electron(s) are transferred,
• Covalent bonding where electrons are shared, and
• Metallic bonding where all atoms loses an e^- and the "communal" electrons just drifts between them.

Bonding classification

Let's start by looking at how, if we only know what elements are present (for example, nitrogen and oxygen), whether it would be possible to predict the kind of bonding that occurs.

Ionic bonds with polyatomic ions

If you can identify that the formula is specifying a species containing a cation and an anion, for example, ammonium sulphate as $$\ce{NH4+}$$ and $$\ce{SO4^{2-}}$$, then you know that there would be an ionic bond between these two oppositely charged ions.

Now complete Questions 1 & 2 in the Practice Stack and check your answers.