The First Group: The Noble Gases

I love these guys. They were only "discovered" a century after the real nobles lost their heads. Lavoisier (and others) were social favourites because they were able to cook up nitrous oxide (laughing gas) for their noble friends. Now that was a noble gas. Robespierre had other ideas, however.

It is unfortunate that the scientific "noble gases" were so named because they were stand-offish, sniffy prigs. Chemically speaking. Like Robespierre. Politically speaking.

So... why are the noble gases "noble?" Why are they so famously inert?

For a very long time, adolescent chemistry learners have been taught by teachers (teachers!!) that the noble gases "want" a full octet. No teacher that I have met has been able to explain why an atom could have such a peculiar desire. Why not a full dozen? Or even a baker's dozen?

Think of it... first of all, the atom, with barely twenty parts, is capable of counting. So it counts up its electrons, discovers that it has only seven, and becomes "dissatisfied." Or it counts up its electrons, finds only two, and becomes discouraged. "What's the use?" says magnesium. "I might just as well give up now, and become an impoverished spinster. Or bachelor. Or whatever gender I am. A single one."

Think of it... an atom, with fewer moving parts than an amoeba, has emotions. And is able to formulate plans to acquire electrons from neighbours. Atoms with twenty moving parts having political ambitions! Think of it! And teachers (!!!!) have been responsible for propagating such silliness.

With the Ross diagram, no such fibbing is required. The first valence shell has the capacity for two electrons. No mystery there. A test tube has a capacity for 25 mL of water. You don't have to credit the test tube with intelligence, or emotions, or political aspirations. The rest of the valence shells have the capacity for eight electrons. Then they are full, and cannot hold any more.

The core charge of the noble gases is very high: 2+ for helium, and 8+ for neon, argon and the rest. The core charge does not get any stronger.

The radius of every noble gas is the smallest in its row. So the valence electrons are very, very close to a massive positive core charge.. they are very difficult to remove.

There you have it. Noble gases can't accept more electrons, because their valence shells are full. Noble gases can't lose any electrons, because their valence electrons are so strongly attracted to the core. Simple? Great.

And you don't have to tell your students that you have never lied in your life.