Noble gases — they just don’t care to bond with anyone.
Since they filled up their valence band, they have no affinity to add more or get rid of any electrons, and are happy just to stay the way they are.
Most other elements, however, feel very differently about their neutral electronic state.
As a result, these atoms tend to bond over their lamentable situation. Ionic bonding just happens to be one way to do it. This requires the atom to ionize, or basically gain or lose electrons and carry a net charge. What an atom is likely to do basically comes down to the attraction and repulsion between charged particles.
But wait, you say, shouldn’t they all just be happy? If you have the same number of protons and electrons, then all should be well and everyone should be happy.
No, no, no, I respond, it’s all about distance! All protons are in the core, and all electrons are in their orbitals; the higher the energy level of the orbital, the further it is from the core and the more loosely bound its electrons are by the nucleus. Plus, the more electrons already attached to the atom, the harder it can be to stick another one in, because all the others are quite literally repulsive.
See, the noble gases are in a fantastic position: they are Goldilocks. Take Ne(on) and its neighboring elements as examples:
- F(luoride) has a lot of protons to hold its electrons, and it could totally take on one more in its 2p-orbital. It will release energy as a result, which is known as the electron affinity energy. In contrast, if you add another electron into neon, it can’t take it in 2p (full) and would need to stick in 3s, which is not only further away from the nucleus but also at a higher energy level. Like trying to feed broccoli to a five-year-old, possibly after giving him/her pizza, you either need to exercise brute force or simply accept that it’s not going to happen.
- On the other side is sodium (Na). Na happens to have a single lone electron in a far-away orbital, and that electron could easily disappear with a flick; this process can be done by putting in just a little energy, known as the ionization energy. This is the case even though Na has one more proton than Ne, because at least with Ne, the outermost electrons are much closer to the nucleus. Similarly, once Na becomes Na+, it’s nearly impossible for it to become Na2+, because it will already be a positively charged bad@$$ with closely held electrons, and you do not want to mess with that.
In summary, for most non-noble gas elements, ionization is pretty likely.
There are quite a few well-known ionic solids, including in the realm of bling: sapphire and ruby are colored versions of the mineral corundum (Al2O3); and spinel is the result of oxygen ionically bonding with magnesium and aluminum (MgAl2O4). In addition, salts are a well-known group of compounds resulting from ionic bonding; their distinguishing feature is their ready ability to dissolve in water. Some common examples include:
- Sodium bisulfate (NaHSO4) and potassium dichromate (K2 CrO7), which are used in photographic bleach;
- Magnesium sulfate (MgSO4), a.k.a. epsom salt;
- Calcium carbonate (CaCO3), which occurs naturally as chalk, limestone, marble, etc.
Of course, the most famous (and arguably simplest) salt of all is….salt.
So how does ionic bonding in salt occur? Well, when a sodium (Na) atom, who has one too many electrons….
…. meets a chlorine (Cl) atom, that has one too few…
(Seriously, have you ever tried hula-hooping with an open loop? It just doesn’t work.)
…they fall in love, talk about life together as a compound, and finally tie the ionic knot.
As a result, Na becomes the cation (Na+), and chlorine becomes the anion (Cl–), and both of them get their noble gas-esque, Ne-or-Ar-like electronic structures. If this isn’t chemistry, I don’t know what is.
I suppose you could say they’re “joined at the hip”, but that seemed like an extreme analogy.
So let’s say they’re three-legged racers instead.
Besides, it’s a pretty good metaphor for the whims of a relationship, no? I mean, compromise and agreement on which foot to move forward is really key to progress. Although I guess if you’re persistent enough, you could get your way anyway…
Fortunately, because sodium chloride (NaCl) is an electrolyte (salt), can dissociate again in certain situations, such as when being dissolved in water.
However, they will continue to exist as ions in water and make it taste funny (or delicious, if you’re cooking!). In fact, the whole reason why water can even pull them apart is in part due to its own electronic polarity, but that’s a story for another day. Given enough time, water will eventually evaporate, leaving the salt crystals to themselves once again.
Please do note, that while you can throw as much water as you want on sodium chloride, and you can use chlorine to clean water, sodium is the last thing you want near water; it will explode, and that’s as good of a reason as any to keep it away.
In short, while the ionic bond is defined as a “give-and-take” relationship, it really isn’t so lopsided at all. In the end, everyone is happy! Just as well, as there are different forms of love, so are there different types of bonding. Stay tuned for Act II!
Sources (accessed on 01-02 Jul 2015):
“Ionization Energy and Electron Affinity.” Purdue University Division of Education. Purdue University.
Nave, Carl. “Common salts.” Hyperphysics.
“Some useful salts.” Eduvee. Edyia Ltd.
“Spinel.” mindat.org. Hudson Institute of Mineralogy.