Ionic Bonding

Bonding actually comes after reactions, equations and stoichiometry in my program, but I reckon that I can explain equations better if I explain bonding first. Plus, as you've seen in my Spec posts, I don't always 100% care about doing stuff in the right order.

Back to the topic of bonding. I'm not talking about relationships here. I'm talking about chemical bonding. Oh, look, did I just make a really bad joke? Moving on...

There are three main types of bonds: ionic, covalent and metallic. Ionic bonds are generally between metal and non-metal elements, covalent bonds are generally between non-metal elements, and metallic bonds are between metal elements. Bet you couldn't work out the last one for yourself!

All right, lame jokes over. Time to talk about ionic bonding. In my last Chem post, Atomic Structure and the Periodic Table, I mentioned the formation of positive and negative ions. If you've forgotten, here it is, in a nutshell: groups 1, 2 and 13 elements lose electrons to become positive ions and groups 15, 16 and 17 elements gain electrons to become negative ions.

These ions become quite important in ionic bonding, hence the name "ionic bonding." You see, when the elements in group 1, 2 and 13 lose electrons, those electrons have to go somewhere. Similarly, the electrons gained by elements in groups 15, 16  and 17 have to come from somewhere. So it's only logical that the metals in the first groups lose their electrons to the non-metals in the latter groups. When they do this, an ionic bond is formed due to electrostatic attractions between the positive and negative ions formed- remember, opposites attract. In fact, opposites attract so damn well that it takes a lot of energy to separate them, resulting in high melting and boiling points.

Despite this, however, most ionically-bonded molecules are soluble in water because they break up into their ions. This is also partially due to the fact that water is a polar molecule and has one end that is slightly positive and another end which is slightly negative- more on this later. The positive ions are attracted to the slightly more negatively-charged end of the water molecule, and vice versa.

Ionically bonded molecules are also non-conductors in the solid form. This may sound surprising, given that they are made up of charged ions, but bear in mind that to let electricity flow these charged particles need to be able to move freely in order to carry the current. In the molten state, however, these particles are a lot more free to move, and thus many molten ionic compounds are conductors of electricity, as are ionic compounds in aqueous solution.

What about the hardness of ionic compounds? Well, ionic compounds generally exist in a lattice of ionically-bonded compounds. In these lattices, negative ions sit next to positive ions, and vice versa, so that the attractive forces between the oppositely-charged ions can hold the lattice together. The hardness of ionic compounds is due to the strength of the attractive forces throughout the lattice. However, when the lattice is bumped hard enough to knock some ions out of place, ions might end up next to other ions of like charges. The repulsive forces between like ions then cause the lattice to shatter. Therefore, ionically bonded compounds are hard, but brittle.