C7- Molecular Compounds Flashcards
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
Tell me the common properties of metals
Solids with high melting points
Shiny (when polished)
Malleable
High density
Good conductors of electricity
Tell me some characteristics of non metals
Solids, liquids, gases with low melting points
Not usually shiny when solid
Brittle when solid
Low density
Poor conductors of electricity
How are atoms in a metallic element structured
The atoms are all the same size and packed closely together in layers to form a giant lattice
Tell me about the sea of delocalised electrons in metals
Metal atoms have 1, 2, or 3 electrons in their outer shell - these outer shell electrons are lost from each atom and become free to move randomly throughout the metal - this leaves a giant lattice of positive metal ions surrounded by a sea of delocalised electrons which randomly move in all directions
What’s Metallic bonding
Is the electrostatic attraction between the positive metal jons and the negative delocalised electrons - this attraction is so strong so metals have high melting and boiling points
What’s malleable
Metals are Malleable so they can be hammered or rolled into shape without shattering
How are metals malleable
When you hit a metal, the layers of ions slide over each other. The sea of electrons holds the ions together and so the metal changed shape instead of breaking
How do metals conduct electricity
The delocalised electrons move randomly between the positive metal ions in all directions - when a potential difference (voltage) is applied between 2 point on a piece of metal, the electrons will flow towards the positive side
The flow of electrons transfers energy and forms an electrical current
What’s it called when a substance can conduct electricity better
They have a higher electrical conductivity
When does the electrical conductivity increase in metals
Is increases in metals when the number of delocalised electrons increases
Eg Na has a 1+ charge but Mg has a 2+ charge so it has a higher electrical conductivity than sodium
Tell me the key points of ionic bonding model
Found in most compounds between metal and non metal atoms
The ionic bonds are formed by the loss and gain of electrons to produce oppositely charge ions that attract one another
The structure is billions of jons held together in a lattice structure
Properties: high melting and boiling points
Many are soluble in water
Conduit electricity when liquid or in solution
Tell me the simple molecular (covalent) bonding model
Found in most non metal elements and compounds
The covalent bonds formed when atoms share pair of electrons
The structure is small in distinct groups of atoms
The properties are
Low melting and boiling points
A few are soluble in water
Most do not conduct electricity
What’s the giant covalent bonding model like
Found in a few non metal elements and some compounds of non metals
The covalent bonds form when atoms share pairs of electrons
The structure is billions of atoms held together in a lattice structure
The properties are
High melting and boiling point
Insoluble in water
Most don’t conduct electricity (except carbon and graphite)
Tell me the key points of the metallic bonding models
Found in all metals
The metallic bonds are the electrostatic attractions between the positive metal ions and negative delocalised electrons
The properties include
High melting and boiling points
Insoluble in water
Conduct electricity when solid or liquid
Tell me the problems with the dot and cross diagram
Shows have electrons are shared but does not show the structure formed and they suggest that all the electrons in different atoms are different- when they are actually all the same
Tell me the problem with the metallic model
Shows the metal ions held in a lattice and explains why it conducts elective but the model does not show that the jons are vibrating all the time
Tell me the problem with the 3D ball and stick model
Show which atoms are joined together and show the shake of the structure - show the atoms are too far apart and there aren’t really stick holding the atoms together
