Revise: Bonding and properties of materialsProperties and bonding in compounds
Only the noble gases exist as individual atoms not bonded to other atoms. In all other substances atoms are held together by chemical bonds, either sharing or gaining/losing electrons.
All ionic compounds have a high melting point and boiling point because many strong ionic bonds need to be broken. They conduct when molten or in solution as the ions are free to move. They can be broken down by electrolysis. They are generally soluble in water.
Covalent network
All covalent network structures have very high melting points and boiling points because many strong covalent bonds need to be broken. They are all hard, and do not conduct electricity because there are no free charges that can move. They do not dissolve.
Covalent molecular
They have low melting points and boiling points because the attractions between molecules are easy to overcome. They do not conduct electricity because there are no free charges to move. Some covalent molecular compounds have higher melting points than expected. Most do not dissolve in water but may dissolve in other solvents.
