What Makes Noble Gases Noble?

The Noble Gases Are Extremely Unreactive

The Group 18 gases are famously "noble" - they don't associate with the "common" elements! The are extremely unreactive, wherever they are found. Why is that? 

1.  Noble Gases Have Very Large Core Charges

The atomic core can be thought of as everything inside the atom except the valence electrons. For Neon, that would be the nucleus, surrounded by the Helium electrons in the 1s² configuration. So... 10 protons in the nucleus, surrounded by 2 electrons in the helium configuration... a total core charge of 8+. That is a very strong core charge, and the valence electrons are strongly attracted to the highly charged atomic core.

2.  Each Noble Gas Has A Very Small Radius

Your students can easily explain why the radius decreases: the stronger the core charge, the more tightly it draws down the valence shell. 
Furthermore, the closer the valence electrons are to the core, the stronger the pull. Students can intuitively use core charge and radius to reason that the noble gas valence electrons are very difficult to pull away from the atom.

3.  Every Noble Gas Valence Is Completely Filled

Of course! In a neutral atom, the number of valence electrons must equal the core charge. Helium has a full 1s² shell. The rest of the noble gases must have 8 valence electrons . All of the noble gases have filled valences. No noble gas atom can receive one more electron.  

4. Noble Gases Can't Win, and Can't Lose!

The Group 18 gases can't lose valence electrons to other elements: the valence electrons are too strongly attracted to the core.

The noble gases can't gain electrons from other atoms: their valence shells are filled!

Because of these two features, Group 18 gases do not react with other elements. 

Become a Better Chemistry Teacher 

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Lesson plans for your students - over 20 lessons and activities covering introductory chemistry.

Teacher guide for you - learning theory, practical tips, and common student traps for each lesson plan.