Covalent Bonding and Molecular Structures Flashcards
What kind of structure does a thermosetting polymer have?
A simple molecular structure
What kind of structure does a thermosoftening polymer have?
A simple molecular structure
Describe the strucuture of a thermosoftening polymer
Tangled long chains of hydrocarbon molecules with no cross links held together by weak intermolecular forces
Describe the structure of a thermosetting polymer:
Long chains of hydrocarbon molecules in layers with cross links between the layers
What is a simple molecular structure?
A structure in which there are strong covalent bonds between atoms but weak intermolecular forces between molecules
What is a covalent bond?
Electrostatic attraction between a shared pair of electrons and the nuclei
What is a common example of a thermosoftening polymer?
Polythene used in plastic bottles, bags etc.
What is a common example of a thermosetting polymer?
Rubber tyres
What are the properties of a thermosoftening polymer?
- Melt at low temperatures
- Soft and flexible
- Soften when heated, harden when cooled and can be re-shaped over and over again
What are the properties of a thermosetting polymer?
- Melt at high temperatures
- Strong
- Resistant to heat and water
- Cannot be reshaped
Why do thermosoftening polymers melt at low temperatures?
It is a simple molecular structure so has weak intermolecular forces between molecules which can be broken easily
Why are thermosoftening polymers soft and flexible?
They have no cross links between hydrocarbon chains
Why do thermosetting polymers melt at high temperatures?
-Due to the cross links between the hydrocarbon chains
Why can thermosetting polymers not be reshaped like thermosoftening ones?
Because, once they are moulded, they do not soften when heated and therefore can not be reshaped because the cross links stop the hydrocarbon chains sliding past eachother and consequently give the polymer strength
Do simple molecular structures conduct electricity?
No, because there are no free electrons to carry the charge
What kind of structure is silicon dioxide?
A giant macromolecular structure
What is the arrangement of atoms like in silicon dioxide?
It is a tetrahedral arrangement:
- Each silicon atom is joined to 4 oxygen atoms
- Each oxygen atom is joined to 2 silicon atoms
Does silicon dioxide conduct electricity? Why?
No because there are no free electrons to carry charge or overall electric charge
What is the special property of silicon dioxide?
It is insoluble in water (it is sand)
What is the melting point of silicon dioxide like? Why?
High because it takes a lot of energy to break the strong covalent bonds
What kind of structure is a diamond made of?
A giant macromolecular structure
What is the arrangement of atoms like in diamond?
Tetrahedral arrangement:
-4 carbon atoms covalently bonded to eachother
Does diamond conduct electricity? Why?
No because there are no free electrons and no overall electric charge
What is the melting point of diamond like? Why?
High because it takes a lot of energy to break the strong covalent bonds
What is the special property of diamond?
Hardest substance because all 4 carbon atoms are covalently bonded making a very strong bond
What kind of structure does graphite have?
A giant macromolecular structure
What is the arrangement of atoms and particles like in graphite?
A hexagonal layered arrangement:
- 3 carbon atoms covalently bonded together
- 4th electron is delocalised into layer
What is the melting point of graphite like? Why?
High because it takes a lot of energy to break the strong covalent bonds
Does graphite conduct electricity? Why?
Yes because 4th delocalised electron can carry charge through the layers
What is the special property of graphite?
It is soft and slippery as the layers in the structure can silde past each other
What is happening as particles condense?
Intermolecular forces are being made
What is happening as particles freeze?
More Intermolecular forces are forming
What is happening as particles melt?
Intermolecular forces are being weakened
What is happening as particles evaporate?
Intermolecular forces are being broken
Describe the particle movement in a gas:
Free moving
Describe the particle movement in a liquid:
Random movement with particles sliding past each other
Describe the particle movement in a gas:
Particles vibrate in a fixed position
What is the special property about a gas?
The particles diffuse to fill a container
What is the special property about a liquid?
The particles flow and take the shape of the container
What is the special property about a solid?
The particles have a defined shape anf volume
What is diffusion?
The spreading of particles due to particle collision
What are the three particle theory assumptions?
- Particles are solid
- Particles are spherical
- There are not forces between particles
Explain the limitation about the particle theory assumption regarding particles are solid:
Apart from the nucleus, atmos are in fact mostly empty space
Explain the limitation about the particle theory assumption regarding particles are spherical:
Particles of different substances have different shapes e.g. polymers are long and thin whereas diamond is tetrahedral
Explain the limitation about the particle theory assumption regarding the lack of forces between particles:
There are forces between particles, otherwise energy would not be needed to separate them when they melt or boil. They also have different strengths whicb arent represented
What is the melting point of a solid?
The temperature at which a solid turns to a liquid. This is because there is sufficient energy to weaken the bonds.
What is the boiling point of a liquid?
The temperature at which a liquid turns to a gas. This is because there is sufficient enrgy to break all the intermolecular forces
Why would a cooling curve have flat points?
- The decrease in the thermal energy of the particles
- means the intermolecular forces increase because slow moving particles are colliding
- the particles therefore have less kinetic energy
- making intermolecular forces requires energy so temperature stays the same and the graph is flat
How are particles represented in the particle theory model?
As solid spheres
Explain how a substance changes from a liquid to a gas when heated
When a liquid is heated, the particles gain energy. The energy makes the particles move faster , which weakens the bonds holding the liquid together. At a certain temperature, the particles have enough energy to break their bonds and the liquid becomes a gas
What is a common use of silicon dioxide? Why?
To line furnaces as it has a high melting point
What is a common use of diamond? Why?
Drill tips as very hard due to 4 covalent bonds for each carbon atom
What is the advantage of a dot and cross covalent bond diagram?
Shows electrons in the bond and from which atom they come from
What are the disadvantages of a dot and cross covalent bond diagram?
Does not show the 3D structure of the molecule
Can become complicated if the molecule is large
What are the advantages of a displayed formula covalent bond diagram?
Shows all bonds and all atoms and how they are connected (particularly in large molecules)
What are the disadvantages of a displayed formula covalent bond dagram?
- Does not show atoms touching
- Does not show the 3D structure
- Does not show the elctrons in the covalent bond and where they have come from
What is the advantage of a 3D ball and stick covalent bond model?
It shows how the bonds are placed in 3D
What is the disadvantage of a 3D ball and stick covalent bond model?
Does not show that the atoms are touching
What is the advantage of a 3D close pack structure model of a covalent bond?
Shows the atoms, the covalent bonds, and their arrangement in space/3D next to eachother
What are the disadvantages of a 3D close pack structure model of a covalent bond?
- Model gets confusing for large molecules
- Do not show bond or electrons and where they come from
What is the relationship between molecular size and the size of the intermolecular forces in simple molecular structures?
As the molecule increases in size, the intermolecular forces increase too (larger molecules have higher melting and boiling points thus)
What is the size of a nano particle?
1-100 nanometres. Atom with a diameter of 0.1nm. Only a few hundred atoms
What is the size of a fine particle (e.g. soot)?
100 - 2500 nanometres. Particle matter up to 2.5 micrometres in diameter
What is the size of a course particle (e.g. dust)?
2500 - 10,000 nanometres. Particle matter up to 10 micrometres in diameter
What is the main property of a nanoparticle?
It has a large surface area to volume ratio
How many carbon atoms make up buckminsterfullerene?
60
What is a fullerene?
Molecules of carbon atoms with hollow shapes
How are the carbon atoms arranged in fullerenes and nanotubes?
In hexagonal rings. Each carbon atom is bonded to three others
What are carbon nanotubes?
Cyindrical fullerenes with a very high length to diameter ratio
What are the properties of a carbon nanotube?
- Have a high tensile strength (don’t break when stretched without adding weight)
- Good conductors of heat and electricity due to 4th delocalised electron
What are fullerenes main uses?
- Used to deliver drugs where they are needed in a controlled way
- Used as an industrial catalyst
- Used as a lubricant
- Used in cosmetic face creams
- Used in sun cream to prevent impact of UV radiation
What are the main uses for carbon nanotubes?
- Strengthen materials
- Used in electronics (ie. microchips)
Why do nanoparticles have different properties from the same material in bulk?
Because of their large surface area to volume ratio, a high proportion of atoms are exposed on the surface of nanoparticles compared to in bulk. This means more of each particle is able to react with the reactants.
What are the advantages of using nanoparticles in drug delivery?
Gets the drug to the affected area quicker and safer and thus there are reduced side affects. Healthy cells are not damaged.
What are some of the concerns regarding nanoparticles?
- The way they affect human health is not fully understood (nanoparticles in sun cream could get into body and cause cell damage)
- May cause environmental damage (silver nanoparticles used in antibacterial fabric could get washed into rivers and they are toxic to fish)
What are the advantages of using nanoparticles?
- Less of them are required than in bulk (faster reactions at less cost)
- Melting points are lower than in bulk (so less energy is required and thus there are less pollutants)
- Many potentials and applications for them
Why is buckminsterfullerene a good lubricant?
It can coat moving parts and reduce friction between them due to the very small and spherical shape of it which means it can fill spaces where there was once friction. it’s molecules will roll due to it’s shape too.
Why are nanotubes useful for catalysts?
- atoms of the catalyst are attached to the nanontube
- this increases the surface area of the catalyst
- therefore there is more chance of reactants colliding with catalysts
