Properties of Covalent Compounds
melting points and boiling points
Most covalent compounds have relatively low melting points and boiling points.
While the ions in an ionic compound are strongly attracted to each other, covalent bonds create molecules that can separate from each other when a lower amount of energy is added to them.
Therefore, molecular compounds usually have low melting and boiling points.
Covalent compounds usually have lower enthalpies of fusion and vaporization than ionic compounds.
Covalent compounds tend to be soft and relatively flexible.
This is largely because covalent bonds are relatively flexible and easy to break.
The covalent bonds in molecular compounds cause these compounds to take form as gasses, liquids, and soft solids.
When dissolved in water, covalent compounds don't conduct electricity.
Ions are needed to conduct electricity in an aqueous solution.
Molecular compounds dissolve into molecules rather than dissociate into ions, so they typically do not conduct electricity very well when dissolved in water.
Many covalent compounds don't dissolve well in water.
There are many exceptions to this rule, just as there are many salts (ionic compounds) that don't dissolve well in water.
However, many covalent compounds are polar molecules that do dissolve well in a polar solvent, such as water.
Examples of molecular compounds that dissolve well in water are sugar and ethanol.
Examples of molecular compounds that don't dissolve well in water are oil and polymerized plastic.