Do covalent bonds dissociate in water?

Answer 1

I'm sure glad you asked! A covalent compound is a compound in which the atoms that are bonded share electrons rather than transfer electrons from one to the other. While ionic compounds are usually formed when metals bond to nonmetals, covalent compounds are formed when two nonmetals bond to each other.

The big question that students frequently have is, "Why do elements share electrons? After all, wouldn't electrons rather grab electrons outright? That's what happens when ionic compounds are formed."

The reason that nonmetals have to share electrons with each other has to do with electronegativity. Recall that electronegativity is a measure of how much an element pulls electrons away from other elements it is bonded to. Metals generally have very low electronegativities (they don't much want to grab electrons) while nonmetals have high electronegativities (they really want to grab electrons). The reason for this trend is the octet rule, which says that all elements want to have the same number of electrons as the nearest noble gas, because noble gases are unusually stable. When metals bond to nonmetals, ionic compounds are formed because the metal atoms don't want electrons and easily give them to nonmetals that do want electrons.

It's a different story when two nonmetals bond with each other. Instead of having one element give electrons to another, we run into a case where we have two elements that have roughly the sameelectronegativity. As a result, neither element can steal electrons from the other. As a result, if either of them are going to be like the nearest noble gas, they'll have to share electrons rather than transfer them.

Answer 2

No they don't.

Simple covalent molecules are held together by really strong covalent bonds and so they cannot disolve as they cannot be pulled apart.

However, do not get these bonds mixed up with the very weak forces holding the molecules together (It's hard to explain without a diagram) which are the reason behind simple covalent molecules' low melting/boiling point.

And again, do not get simple covalent molecules mixed up with covalent giants, which have a very high melting point - but that's another question.

Answer 3

The solubility of a covalent compound depends upon the polarity of the covalent bond, which depends upon the electronegativity of the involved elements. For example, hydrogen fluoride has a very polar bond and dissolves in water. On the other hand, methane has no polar bonds and does not dissolved in water.

Answer 4

No, covalent bonds do not dissociate in water at standard conditions. Ionic bonds do dissociate.