What are the functional differences between covalent and ionic bonds?


I understand that covalent bonds deal with non metal elements, and ionic bond metals and non metals. Is this the only difference? From my understanding, covalent bonds ‘share’ an electron, while ionic bonds form from one atom ‘steals’ an electron from another but the difference is for whatever reason eluding me.

In: 1

First off: the distinction between ionic and covalent isn’t sharp. There’s always some degree of sharing/stealing in any bond, it’s just that most bonds lean much more toward one than the other.

Your understanding of covalent = sharing and ionic = stealing is basically correct, so you know what an ionic bond *is*. (Bonds in the middle of this spectrum are called *polar covalent* bonds, and they share some of the characteristics of both extremes. The hydrogen-oxygen bond in water is a good example.)

As for why you’d care:

* Ionic compounds tend to have different molecular shapes. In covalent bonds, the shape of the shared electron orbitals forces particular shapes, described pretty accurately by [VSEPR theory](https://en.wikipedia.org/wiki/VSEPR_theory) in most cases. In ionic bonds, the charged atoms just shove themselves into as tight a pattern as possible.

* Small molecules with ionic or polar-covalent bonds are usually soluble in water; non-polar covalent bonds are often not soluble in water. The reverse is true for non-polar solvents like oils.

* Ionic compounds almost always create highly conductive solutions when dissolved in water.

* Ionic solids have very high melting and boiling points relative most covalent compounds, because their structure is quite rigid. For the same reason, ionic solids tend to be very hard.

Well, it’s to do with the orbitals. An orbital is where an electron probably is. It’s a quantum object so it doesn’t actually be in a place the way we’re used to it, but the orbital is where it’s likeliest to be found. When an electron moves to a different atom, its orbital is now entirely around the new ion. In a covalent bond, the orbital stays on the same atom, but gets skewed towards the second atom.

The functional difference is that atoms in ionic bonds can move around each other. Basically in an ionic bond an electron completely leaves one of the atoms and moves to the other. This can happen for a lot of reasons. So now you have a positively charged atom and a negatively charged atom. This difference in charge holds the atoms together (positive attracts negative).

However, in a covalent bond the atoms are held together in very specific positions, almost like a metal bar is holding them together. Ionic bonds are just held together, but not at any specific angle or position. They’re just generally pulled together.

This is why ionic compounds tend to dissolve a lot better. Because they can move a lot more freely in a solution.

So while non metal to metal forms ionic bonds a lot, you can actually get ionic bonds in other situations. For instance water is usually two hydrogen atoms covalently bonded to an oxygen, but in water some small amount of it will ionize. One of those covalent bonds will become ionic. How much this happens is actually what we are measuring when we measure pH.

You might also want to Google electronegativity and have a read it will help you understand the properties of different valencies and why they lead to a covalent or ionic bond.