Atom
Number of Electrons
Ne10
Na11
Those are Ne and Na electron configuration
Now Atomic radius:
For Ne: 38 pm
For Na: 190 pm
The reactivity of Na is higher than Ne because Ne has the last orbital complete. Na has only one electron in the last orbital.
We can also say that the reactivity of metals increases further to the left in the period (fewer electrons to remove).
The reactivity of metals increases as they move up a group (greater tendency to lose electrons).
Noble gases, which, although they belong to the main elements because they are very stable due to the fact that they have their last orbital full (i.e., they have eight electrons in their valence shell), are not very reactive.