Chemistry · Ch 6 — Solid State
Covalent Solids
Covalent Solids
In a covalent (network) solid, the constituent atoms are bound together in a continuous three-dimensional network entirely by covalent bonds -- there are no separate 'molecules' at all; the whole crystal is, in effect, one giant molecule. Diamond and silicon carbide are the standard examples.
Because every atom is locked into this covalent network, such crystals are exceptionally hard and have very high melting points -- an enormous number of strong covalent bonds must be broken to melt or deform the solid. They are also, as a rule, poor conductors of both heat and electricity, since (unlike a metal) there are no delocalised electrons free to carry charge or transfer thermal energy quickly. …
Worked out. A short aside noting that graphite is used inside pencils: it slips easily off the pencil onto the paper and leaves a black mark, and it is also a component of many lubricants -- for example bicycle chain oil -- precisely because it is slippery. This flags graphite as an instructive exception within the covalent-solid family: its layered structure (strong covalent bonding within each layer, weak forces between layers) is what gives it this slipperiness and, unusually for a covalent solid, usa …