C7- Molecular Compounds Flashcards
(41 cards)
What are compounds
Things that contain atoms of more than one atom, CHEMICALLY joined together by bonds
Some compounds exist as molecules they have …. Structures
They have covalent, simple molecular structures
Eg water
How can intermolecular forces that hold WATER or a liquid together be overcome
Turning the water into a gas
Why do simple molecules mostly have low Melting and boiling points
It doesn’t take much energy to overcome the weak intermolecular forces
How do you break covalent bonds
They have strong forces of attraction so have high melting and boiling points
What charge do simple molecules have
No charge - neutral
So they can’t carry an electric current
Why can’t covalent bonds carry an electric current
The strong forces between the negatively charged electrons and the positively charge nuclei hold the electrons in place so the electrons can’t flow and so carry a current
What are monomers
Are small simple molecules that can be joined in a chain go form a polymer
What’s a polymer
Lots of monomers joined together
How are monomers usually linked
By covalent bonds between the atoms
What do most polymers contain
A chain of carbon atoms
What’s polythene
A common polymer made of ethane monomers
Tell me about the length of polymer molecules
The longer polymers have more intermolecular forces between them
The longer chains also tend to get tangled up with one another for these reasons, longs polymers have higher melting and boiling points than shorter ones
What are molecules
Groups of atoms joined by covalent bonds
Can be compounds too eg water
What’s an allotrope and give me an example
Different structural forms of the same element are called allotropes
The structure and bonding in different allotropes influences their properties and uses
Carbon can form a number of different molecules
What’s a fullerene
Carbon can from simple molecules called fullerenes in which each carbon atom is covalently bonded to three other carbon atoms
Fullerenes are often tubular molecules (nanotubes) or spherical.
Tell me about fullerene melting and boiling points
They have weak intermolecular forces between the molecules and so have low melting points (or sublimation points) these weak forces also make them soft and slippery - however the molecules themselves are very strong due to their covalent bonding
Tell me about graphene
Similar to fullerenes but it’s not a simple molecule
Consists of a sheet of carbon atoms with no fixed formula
Sheet just 1 atom thick making it the lightest known material
Covalent bonds make it extremely strong
Allows free electrons to move across its surface and so is a good electrical conductor
Tell me about diamond and graphite
Two more allotropes of carbon
Both examples of covalent, giant molecular structures which have huge 3D networks of atoms linked by covalent bonds
Both have high melting points Becuase of the strong covalent bonds that need to be broken to melt the solids
Compare diamond and graphite
Graphite has 3 covalent bonds for each carbon atom whereas diamond has four
This gives graphite a layered structure and means that not all of its electrons are held in covalent bonds - delocalised electrons
What are delocalised electrons
Free electrons that aren’t in covalent bonds - they are free to move and carry an electrical current
Why is graphite used for electrodes in electrolysis
It conducts electricity due to delocalised electrons and is cheap and not very reactive
Why is graphite useful as a lubricant
The sheets of carbon atoms in graphite are held together by weak forces of attraction between layers - these weak forces allow the layers to slide past eachother which makes graphite soft and useful eg a lubricant
Why is diamond very hard
Becuase it has a rigid network of carbon atoms in a tetrahedral arrangement, joined by strong covalent bonds
This property makes diamond useful for tools to cut things
It’s also an electrical insulator Becuase it had no free charged particles
