admin | Thu, 09/07/2017 - 07:06
Good question. In section 2.4 boron is classified as a metalloid, not a metal. It actually forms covalent bonds, not ions, and so is a molecule.
The rules we use are "rules of thumb," for example, we say a metal and a nonmetal form an ionic compound. Well, in the solid state, AlF3 does, and it forms a crystal. But in the gas phase, it forms a molecule, AlF3, with three covalent bonds.
As for nomenclature, the rules work pretty good, and the way things often work is that you learn a set of rules, then you learn about where they break down, and what the exceptions are. So in lecture, you should pay close attention to the exceptions we discuss, especially when we get to the chapters on periodic trends, which I think are around chapter 7.