Chemistry / Unit 5 Chem 0859 short lesson, about 20 seconds
Core Electrons Versus Valence Electrons
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The idea
Valence electrons occupy an atom's outermost shell, while core electrons fill the complete inner shells beneath, matching a noble gas's configuration.
In practice
Sodium's configuration, [Ne]3s¹, shows its ten core electrons abbreviated as [Ne], leaving one valence electron in the 3s orbital.
Where people slip
Chemical reactivity is governed chiefly by valence electrons — core electrons are shielded from most chemical interactions by the shells outside them.
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