A covalent bond is the electrostaticattraction between twonuclei and a sharedpairofelectrons.
covalent bonding forms molecules
simple molecular structure and boiling point
contains many individual covalently bonded molecules held together by weak intermolecular forces of attraction
low boiling point as the weak intermolecular forces need to be broken
as the mass of the structure increases (mr increases) the intermolecular forces get stronger and boiling point gets higher
giant covalent structureand boiling point
many atoms all covalently bonded together
eg. diamond, graphite, silicon dioxide
very high boiling points as you need to separate the strong covalent bonds
no ions or delocalized electrons so poor conductors
apart from graphite
graphite
layers of giant covalent structures (hexagonal lattice structures of carbon) (called graphenes) with weak forces of attraction holding them together so they can slide over eachother - making it soft and why it is used as a lubricant
layers have delocalised electrons between them which are free to move so can conduct electricity
high melting point because of strong covalent bonds
do covalent structures conduct electricity
covalent structures generally don't conduct electricity as they lack ions or delocalized electrons
how are covalent bonds formed
Covalent bonds are formed when two non-metal atoms share pairs of electrons to achieve a full outer shell.
diamond
tetrahedral lattice of carbon atoms
giant covalent structure
high melting point as many (because of tetrahedral shape) strong (covalent) bonds need to be broken.
hard as lots of energy required to scratch and break strong covalent bonds
c60 (buckminster) fullerene
Its molecules are made up of 60 carbon atoms joined together by strong covalent bonds in a hollow sphere.
There are weak intermolecular forces between molecules of buckminsterfullerene, so is slippery and has a low melting point.
can't conduct electricity as delocalized electrons can't move across molecules