• This LAS seeks to introduce the three main types of bond in chemical substances: ionic, covalent, and metallic.
• An additional hidden purpose is to suggest the idea of aqueous solutions, and how ions of the salt (the solute) are floating in solution because of their interactions with the water molecules (the solvent). As soon as the water molecules are gone, the ions can no longer float, so they precipitate. There is no need to discuss this in class, the intention is only to get the students to start thinking about it, perhaps without realizing it.

• 18 K (“eighteen-carat”) gold in a ring: metallic.
• CO₂: covalent.
• KF: ionic.
• Steel in a ship: metallic.

• In a  way, metals are a type of crystal, in the sense that they are ordered atomic lattices.
• Pure gold is too soft to use in a ring (it would deform), so jewellers mix it with other harder metals such as copper, silver, and nickel.
• Pure gold is 24 K, so 18 K gold is about 75% pure.
• Iron rusts (oxidizes) too easily, particularly near seawater. For this reason, steel is made by adding carbon, titanium, nickel, tin, and other elements to iron. Steel is much more resistant to oxidation than iron.

• Actually, steel is a bit of a complicated material. It’s not just a simple metal, since carbon itself is not a metal. In fact, the main role of the small amounts of carbon in steel is to decrease the metallic properties of iron (the ductility and conductivity), so that it becomes harder and less easy to oxidize.

References

• Brown et al. The Central Science, 14th Ed. Pearson (2017). ISBN:978-1292221229.

Authors and contributors

This LAS was developed by Dr. Victor Sojo, with helpful contributions from Dr. Christopher Bernido, and Dr. Marivic Bernido.