(SC7) Types of Substances Flashcards
Molecular compounds are…
distinct groups of atoms joined by covalent bonds
Molecular compound’s melting and boiling points (why?)
The covalent bonds are strong forces of attraction. However, there are also weak forces of attraction between molecules - intermolecular forces. These forces hold molecules together and must be overcome when turning liquid to water. It doesn’t take much energy to overcome the weak intermolecular forces, that’s why melting and boiling points are relatively low.
Conduction of electricity
Simple molecules have no overall charge so cannot carry an electric current. The strong forces of attraction hold electrons, which due to these forces cannot flow. Therefore, molecular compounds cannot conduct electricity.
Polymers are…
chains of joined monomers
Polymer’s boiling and melting points
Longer polymers have more intermolecular forces between them. The longer chains also tend to get tangled up with one each other. That’s why longer polymers have higher melting and boiling points than shorter ones.
Molecules are…
groups of atoms joined by covalent bonds
Allotropes are…
different structural forms of the same element.
Fullerenes are…
simple molecules in which each carbon atom is covalently bonded to three other carbon atoms. Fullerenes are often tubular or spherical.
Fullerenes’ properties
Fullerenes have weak intermolecular forces between the molecules and so have low melting and boiling points. These weak forces also make them soft and slippery. However, the molecules themseleves are very strong due to their covalent bonds.
Graphene is…
similar to fullerene but is not a simple molecule. It consists of a sheet of atoms with no fixed formula.
Grapene’s properties
The sheet is just one atom think, making it the lightest known material, but its covalent bonds make it extremely strong. It also allows free electrons to move across its surface and so its a good electrical conductor.
It is used for anti-corrosion paints, efficient electronics, efficient solar panels.
Graphite is…
a covalent, giant molecular structure made up by layers of graphene.
Graphite’s properties
Graphite has 3 covalent bonds for each carbon atom, which means not all electron are held in covalent bonds. These delocalised electrons are free to move and can carry electrical current. That’s why it is used as electrodes.
Sheets of carbon atoms in graphite are held together by weak forces of attraction. These weak forces allow the layers to slide past each other, which makes graphite quite soft and useful as lubricant.
Diamond is…
a covalent, giant molecular structure made of carbon atoms.
Diamond’s properties
Each carbon atom has 4 covalent bonds, which means that it can’t conduct electricity because it doesn’t have delocalised electrons. It is an electrical insulator.
Diamond is very hard because 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.
