C3: Structure and Bonding Flashcards
What are the properties of solids?
They are hard to compress
- packed in a regular pattern with almost no space between particles
Fixed shape - cannot flow
Vibrate in place
What are the properties of liquids?
Hard to compress
-particles are close together with little space
Take the shape of the container, can flow
Slide along each other
Particles vibrate faster
What are properties of gas particles?
Easy to compress
- particles are far apart
Spread out to fill the space of the container
Move quickly and randomly
Why is it harder to change the state of some materials?
Some have stronger intermolecular forces of attraction, thus more energy is required to break them, thus the higher the melting point
What are the limitations of the simple particle model?
The model assumes all particles are solid spheres (particles have different shapes and are not solids)
Forces between particles are not shown (incorrect)
What is ionic bonding?
The bonding taking place between a metal and a non-metal. It takes place for both to achieve a full outer shell
What is a dot and cross diagram?
A diagram representing ionic bonding - only needs to show outer energy levels. Usually, metals are modelled with crosses as their electrons and non-metals are modelled with dots to distinguish the electrons.
To model ions add square brackets around the ions and the sign on the outside
What are the properties of ionic compounds?
They form giant ionic lattices (every + ion is surrounded by a - ion)
Cannot conduct electricity when solid, but can when liquid
What are the properties of giant ionic lattices?
Very strong electrostatic forces (ionic bonds) of attraction - high m.p. and b.p., lots of heat to break
Why can’t ionic structures conduct electricity when solid?
Their ions are locked in place by the electrostatic forces of attraction. They conduct when liquid because then, the ions can move and carry a charge
What is covalent bonding?
Takes place between two non-metals. They share pairs of electrons to form full outer shells
How is covalent bonding modelled as energy level diagram?
The atoms are modelled as circles with their electrons modelled as dots and crosses respectively (only outer shells required). Their bond is shown as an overlap, with their shared electrons inside the overlapping space
Why do small covalent molecules have low m.p. and b.p.?
Although the atoms are held together by strong covalent bonds, the intermolecular forces between the molecules are very weak, thus require low energy to break
What happens to m.p .and b.p. of covalent structures as their size increases?
They increase, this is because there are now more intermolecular forces, which need more energy to break.
Why don’t small covalent molecules conduct electricity?
Covalently bonded molecules have no charge, thus cannot carry a current
What is the structure of giant covalent molecules?
Many covalently bonded molecules joined together in a giant covalent lattice
What are the properties of giant covalent molecules?
Always solids at room temp.
Why are giant covalent molecules solids at room temp.?
They have millions of strong covalent bonds, taking more energy to break them
What is the structure of diamond?
Each carbon atom forms 4 covalent bonds with other carbon atoms - a single diamond contains a huge amount of these covalent bonds, resulting in a very high melting point
Why can’t diamond conduct electricity?
It contains no free electrons to carry electrical charge
What is the structure of silicon dioxide (silica or sand)?
Oxygen atom covalently bonded to a silicon atom - it has a huge number of these
What are the properties of silicon dioxide?
High melting and boiling points
What are the properties of graphite?
High m.p. and b.p.
Soft and slippery
Excellent conductor of electricity and heat
What is the structure of graphite?
Carbon atoms with 3 covalent bonds each. They form many hexagonal rings (as there’s a lot of them, graphite has a high m.p. and b.p.). These are arranged in layers which are not covalently bonded, thus they can slide, making graphite slippery. Instead, they are held together by the single electron of each carbon atom which is not in a covalent bond
Why is graphite a good conductor of heat and electricity?
Delocalised electrons can move, meaning they can conduct heat and electricity
What is graphene?
A single layer of graphite, one atom thick
What are the properties of graphene?
Excellent conductor of electricity (has delocalised electrons)
Extremely strong
Where is graphene used?
Electronics, medicine, transport
What are fullerenes?
Molecules of carbon atoms with hollow shapes, they usually have hexagonal rings of carbon atoms
What’s the name of the fullerene that was in the first question of last year’s mock paper and what is its shape?
Buckminsterfullerene - sphere
What are the uses of fullerenes?
Pharmaceutical delivery
Lubricants
Catalysts
What are the uses of carbon nanotubes?
High tensile strength - stretched w/o breaking
Excellent conductors of heat and electricity
What is the structure of metals?
A giant structure arranged in layers, electron on their outer shells are delocalised
What is metallic bonding?
The bonding between two metals, they have a ‘sea of delocalised electrons’. As they have now lost their outer electron, a positive metal ion is formed. Thus, there is now a strong electrostatic attraction (metallic bond) between the delocalised electrons and the positive metal ions
What are the properties of metals?
High m.p./ b.p.
Conduct heat and electricity
Can be bent and shaped
Why do metals have high m.p. and b.p.?
They have strong metallic bonds, taking a lot of energy to break
Why are metals good conductors?
They have delocalised electrons which can carry charge and move around (passing the energy more quickly)
Why can metals be bent and shaped?
The layers of atoms in metals are able to slide over each other
How can metals be hardened?
Make an alloy
What is an alloy?
A mixture of metals
- different sizes of atoms distorts the layered structure of the metals, making it more difficult for them to slide over each other - making them harder than pure metals
What is the value of a nanometre?
1 nm = 1/1,000,000,000 m
1nm = 1/1,000,000 mm
1nm = 1/1000 mum
What is the size of nanoparticles?
1 - 100 nm diameter
- contain only a few hundred atoms
What happens when you decrease the particle size?
The SA:V ratio increases by the same amount
What is the SA:V ratio of nanoparticles?
Huge, a much smaller quantity of nanoparticles is needed compared to a normal sized particles
What are the uses of nanoparticles?
Sunscreens
Cosmetics
Deodorants
Electronics
Catalysts
Medicines
What are the risks of nanoparticles?
They can be absorbed into the body and enter cells
- causing breathing problems
- washing clothing with silver nanoparticles can harm aquatic life
