C2.2 How structure influences the properties and uses of substances Flashcards
Do simple molecules conduct electricity?
No
Why do simple molecules not conduct electricity?
because the molecules do not have an overall change
Why do ionic compounds have high melting and boiling points?
as there are strong electrostatic forces in all directions between oppositely charged ions. Large amounts of energy are needed to break many strong bonds
When can ionic compounds conduct electricity, why?
when melted or dissolved in water.
can conduct electricity because ions can move and carry a current
give an example of an ionic compound
sodium chloride
Why do giant covalent structures- macromolecules, have high boiling and melting points?
As all atoms are linked to other atoms by strong covalent bonds.
How many covalent bonds does carbon form in diamond?
4
How many covalent bonds does carbon form in graphite?
3
Why are there layers in graphite?
As each carbon atom bonds to 3 other carbon atoms
Why is graphite soft and slippery?
each carbon bonds with 3 other carbon atoms which forms layers. Layers are free to slide over each other as there are no covalent bonds between the layers so therefore weak intermolecular forces between layers.
Why can graphite conduct electricity?
One electron from each carbon atom in graphite is delocalised. These delocalised electrons allow graphite to conduct heat and electricity
Describe the structure of fullerenes
hexagonal rings of carbon atoms
What can fullerenes be used for?
drug delivery into the body. in lubricants, as catalysts, and in nanotubes for reinforcing materials eg in tennis rackets
What does conduction depend on?
the ability of electrons to move throughout the metal
Why do metals conduct heat and electricity?
because of the delocalised electrons in their structures
Why can metals be bent and shaped?
atoms arranged in regular layers. These layers are able to slide over each other.
Why are alloys harder than pure metals?
Alloys are made from 2 or more different metals. The different sized atoms of the metals distort the layers in the structure, making it more difficult for them to slide over each other.
Give an example of a shape memory alloy
Nitinol used in dental braces
What do shape memory alloys do?
return to their original shape after being deformed
What do the properties of polymers depend on?
what they are made from and the conditions under which they are made
What conditions are needed to make low density polythene?
high temperature and pressure
What conditions are needed to make high density polythene?
Lower temperature and pressure
catalyst
Describe the structure and properties of thermosoftening polymers
individual, tangles polymer chains. Weak intermolecular forces between chains so easy to separate, melt and recycle
Describe the structure and properties of thermosetting polymers
polymer chains with cross links (covalent bonds) between them so strong intermolecular forces between bonds. Means that they do not melt when heated- high melting point so can not be recycled
What structures does nanoscience refer to?
structure that are 1-100 nanometers in size and contain a few hundred atoms.
4 key points about nanoparticles
- 1-100 nanometers in size
- contain a few hundred atoms
- nanoparticles show different properties to the same materials in bulk
- have a high surface area to volume ratio
What can nanoparticles be used to make?
new computers, catalysts, stronger and lighter construction materials, new cosmetics
Why do substances that consist of simple molecules have relatively low melting and boiling points?
There are weak intermolecular forces between the molecules. It is these intermolecular forces that are easily overcome, not the strong covalent bonds when a substance melts or boils.
Why is silica used to make brinks for high temperature furnaces?
It has a high melting point (it is a macromolecule)
because each silicon atom is covalently bonded to 4 oxygen atoms
These covalent bonds are very strong so a lot of energy is needed to break them
it is unreactive , hard and a poor conductor of heat as there are no free electrons
Explain why nanoparticles pass through the skin and travel around the body more easily than normal-sized particles
as they are smaller- only a few atoms in size
so they can easily pass through the skin
Explain why thermosoftening polymers would not be suitable for packaging very hot food
They have a low melting point so would melt
This is because there are no crosslinks between chains
so there are weak intermolecular forces
Why is silicon dioxide a suitable material for lining furnaces?
It has a high melting point (as it is a macromolecule)
because a lot of energy is needed to break bonds
This is because the bonds are covalent and so are very strong
Explain why copper is a good conductor of electricity
Copper has delocalised electrons which can move through the structure and carry a charge
Explain why carbon dioxide has a very low boiling point
Carbon dioxide is simple molecular
There are weak intermolecular forces between the molecules
so only a small amount of energy is needed to separate the molecules
Explain why graphite is softer than diamond
because there are layers in graphite that can slide
this is because there are only weak intermolecular forces between layers
however in diamond, each carbon atom is covalently bonded to 4 others
so no carbon atoms are able to move
Explain hy graphite conducts electricity but diamond does not
because graphite has delocalised electrons which can carry a current and move throughout the structure
however, diamond has not delocalised electrons
Suggest why carbon nanotubes are used as lubricants
nanotubes can slide over each other
because no covalent bonds between the nanotubes
