SC7 Types of Substances Flashcards
What are giant covalent structures?
Structures wherein many covalent bonds have been used to join the substance together
What are the properties of giant covalent substances?
- high melting and boiling points
- no conduction of electricity
- insoluble in water
Why do giant covalent substances have high melting and boiling points?
They are solids at room temperature, which tells us that the covalent bonds that hold them together are strong and need lots of energy to break
Why can’t giant covalent substances conduct electricity?
They carry no overall charge, so they can’t conduct electricity
Why are giant covalent substances insoluble in water?
Giant covalent substances can’t form strong attractions with water, so they can’t dissolve in it
What are some examples of allotropes of carbon?
- Diamond
- graphite
- graphene
Describe the structure and bonding of diamonds
- each carbon atom is joined to four other carbon atoms through a covalent bond
- form a regular tetrahedral structure
- no free electrons
Describe the properties of diamond
- high melting and boiling points
- doesn’t conduct electricity
- hard
What are some of the uses of diamond?
- used to cut hard things
- worn as jewellery
Describe the structure and bonding of graphite
- each carbon atom is joined with three other carbon atom
- carbon atoms form a hexagonal layered structure
- layers have weak forces of attraction between them, which means that it can easily slide over each other
- each carbon atom has one un-bonded outer electron
- these are the free electrons, and they are delocalised
Describe the properties of graphite
- slippery
- high melting and boiling points
- can conduct electricity due to the delocalised electron
What is graphene?
A single layer of graphite
What are fullerenes?
Molecules of carbon with hollow shapes. Their structures are based on hexagonal rings of carbon atoms.
State two examples of a fullerene
- nanotubes
- Buckminster balls
What are the properties of a fullerene?
- low melting and boiling points
- soft
- slippery
Define polymer
A large molecule which is consists of many identical smaller molecules known as monomers
What are carbon nanotubes?
Cylinder fullerenes with a high length to diameter ratios
What are the properties of graphene?
- can conduct electricity due to the delocalised electrons
- strong
- high melting point
Describe the properties of a Bucky Ball
- consists of weak intermolecular forces which need little energy to overcome
- lower melting points compared to diamond or graphite
Describe the properties of a nanotube
- high tensile strength, so they are strong in tension and can resist being stretched
- strong
- can conduct electricity
Explain the state most polymers are in at a room temperature
They are in a solid state because the intermolecular forces are relatively strong
Describe some common properties of metals
- solids with high melting
- shiny
- malleable
- high density
- good conductors of heat and electricity
Describe some common properties of non-metals
- solids, liquids or gases with low melting points
- not usually shiny when solid
- brittle
- low density
- poor conductors of heat and electricity
Describe the structures of graphite and diamond.
Graphite
- Giant molecular structure.
- Each carbon atom is bonded to three others.
- Weak intermolecular forces between layers.
- strong covalent bonds between atoms in a layer.
Diamond
- Giant molecular structure.
- Each carbon atom is bonded to four others.
- Strong covalent bonds between atoms.
- High boiling and melting points.
Explain the properties of fullerenes including C60 and graphene in terms of their structures and bonding.
Graphene
- Each carbon atom is covalently bonded to three other carbon atoms.
- Very strong and flexible.
- Conducts electricity as electrons are free to move.
Fullerene
- Has carbon atoms arranged in pentagons as well as hexagons.
- Conducts electricity as they have delocalised electrons.
- Are soft when in solid state as they have weak intermolecular forces.
Explain, in terms of structure and bonding, why graphite is used to make electrodes and as a lubricant, whereas diamond is used in cutting tools.
- Graphite has weak intermolecular forces between layers, so they can slide off each other.
- Graphite has free electrons which carry a charge, allowing it to conduct electricity.
- Diamond has strong covalent bonds between atoms.
- Diamond also has high melting and boiling points
Describe the structure and bonding of metals
The electrons in the outermost shell ‘leave’ the atom, forming positive ionic lattice in a sea of delocalised electrons
Why are metals malleable?
Layers of ions can slide over each other without breaking when a force is applied
What is metallic bonding?
The electrostatic attraction between the metal ions and the sea of delocalised electrons
Why can metals conduct electricity?
The delocalised electrons move through the lattice when a voltage is applied. This carries the charge forming an electric current
What is a bonding model?
A description of how a chemical bond is formed and/or the structure produced by atoms
What does a dot and cross diagram show?
- how the ionic bonds are formed
- the ratio in which atoms react
What are the limitations of a dot and cross diagram for ionic compounds?
- doesn’t show the ionic lattice
- doesn’t show the ionic bonds
What are the limitations of a chemical formula as a bonding model?
- doesn’t show charges
- doesn’t show arrangement of atoms
What are the limitations of a 2d diagram?
- doesn’t show how bonds were formed
- doesn’t show the other layers
What are the limitations of a 3d diagram?
- doesn’t show the attraction between the molecules
- isn’t to scale
What are the limitations of a ball and stick model?
It doesn’t show
- the sticks are actually forces
- how covalent bonds are formed
What are the limitations of the space filling model?
- we don’t know which elements are which
- doesn’t show how the covalent bonds were formed
What are the limitations of a dot and cross diagram for covalent bonds?
It doesn’t show:
- relative sizes of the molecules
- intermolecular forces
