In: Chemistry
what makes the noble gases "noble"?
To answer this question, we have to talk a little about atoms.
All elements have negatively charged electrons bound in states
around the positively charged nucleus. These states are wave
patterns, like the patterns a string or a drum make as they
vibrate. Only certain energies of states are possible, sort of like
how a musical instrument vibrates at only special frequencies. It
turns out that it's impossible for more than one electron to be in
the same state. Electrons fill up the lowest energy states closest
to the nucleus of the atom first, and then gradually fill up the
higher energy states.
There's a pattern to how the energies increase as more states fill
up. Some of the states have about the same energy, then there's a
jump up to the next level. Atoms are most stable when adding
another electron would mean having to jump up to the next energy
level. The noble gases are the atoms like that. The electrons they
have are tightly bound but the next electron to come along wouldn't
be. So they tend to just stay as they are, not giving up or gaining
electrons, or sharing electrons with other atoms. That means that
the atoms don't stick together into molecules.
On the other hand, the most reactive elements are those that have
one extra electron or are missing one, compared to a noble gas.
Sodium (Na), for example, has one more electron than neon. That
last electron can come off and stick to another atom that has an
empty state at low energy, such as fluorine (F), which has one less
electron than neon. Since the Na is left with a positive charge and
the F is left with a negative charge, they attract and tend to
stick together as HF molecules.
Interestingly, the "noble" in noble gas refers to a meaning of the
word noble that we don't often think of: this noble means "having
admirable properties." It was given this name because they are not
very common on earth, and so their inertness was very rare compared
to other elements.