Giant Molecular Structures Flashcards
Carbon has __ electrons in its outermost energy level and it shares all of these electrons when it bonds.
4
What happens when carbon atoms bond to other carbon atoms?
Giant molecules or macromolecular structures are formed.
What is an allotrope?
[“Allotropes are different structural forms of the same
element”]
Comment on the physical state of giant molecular structures?
All substances with a giant molecular structure are solids. The solid structure has many covalent between the atoms, which make it quite hard.
Comment on the melting and boiling points of giant molecular structures.
High
Why do giant molecular structures have high boiling and melting points?
This is because strong intramolecular bonds (covalent bonds) must be broken to melt and boil them.
Why do giant molecular structures not conduct electricity?
For electricity to be conducted, there must be a movement of free mobile electrons. All the outer shell electrons in the atoms of covalent structures are used to form covalent bonds. Thus there are no free mobile electrons and the conduction of electricity does not occur.
Comment on the solubility of giant molecular structures.
Substances with a giant molecular structure are insoluble in any solvent.
Why does diamond have a high boiling point?
Substances with a giant molecular structure comprised of strong intramolecular bonds require a lot of energy to break them.
Why are diamonds very strong, and yet considered to be brittle?
The strong covalent bonds throughout the diamond make it the hardest natural substance.
Diamond is used to cut other hard solids (because of its own hardness). All the covalent bonds between the molecules are very strong, so the diamond is hard and brittle (opposite of malleable).
Why is graphite very soft?
Graphite, like a diamond, is a form of carbon and has a giant molecular structure. However, the
properties of graphite differ from those of diamond. This is because graphite has a different
structure. The forces between the layers of carbon atoms are weak and so they can easily
slide past each other. This makes graphite soft and slippery. The delocalized electron is free
to move along horizontal slippage planes.
Why does the graphite sublime at a high temperature?
To sublime graphite, it isn’t enough to loosen one sheet from
another by breaking the weak intermolecular bonds. You must break the intramolecular bonds
– the covalent bonds throughout the whole structure. THIS REQUIRES A LOT OF ENERGY IN
THE FORM OF HEAT.
Why is graphite a good conductor of electricity but diamond is not?
Graphite is the only non-metal that conducts electricity. It can do this because, in a layer of graphite, each carbon atom is bonded to three other carbon atoms. For every three covalent carbon-carbon bonds, one delocalized electron is free to move between these layers of carbon. Thus, graphite is used for contacts in electric motors and forms the positive terminal in the common dry cell battery.
Why are graphite and diamond insoluble?
Attractions between solvent (e.g. water) molecules and carbon atoms will never be strong enough to overcome the strong covalent bonds in graphite.
Why does graphite have a lower density than a diamond?
This is because of the relatively large amount of space
that is “wasted” between the sheets.
