we can measure the properties of several unknown solids by some of the characteristics :
Covalent.
Ionic.
Metallic.
Network covalent.
covalent bonds are weaker than ionic and create molecular compounds. these have low melting and boiling points.
ionic compounds are very strong bonds, it takes a lot of energy to melt and boil these compounds. these are brittle compounds.
metallic bonds are found in metals, of course. these are described as "sea of electrons" because the valence elctrons of each metal atom can freely move between the metal atoms in the crystal. this is what allows for electric conductivity in metals, the easy flow of electrons through the metal.
network covalent are covalent bonds. the are different from covalent bonds because they are much stronger bonds. a diamond is made only of C. one sees in other compounds that carbon bonds are covalent and weaker than ionic. in a diamond, the C atoms are in a network of covalent bonds and, as we see everyday, graphite, also only carbon, is so weakly held together that we can rub the tip of a pencil and the C comes off on our hands