CC7 Flashcards
How many elements do all compounds contain?
All compounds contain atoms of more than one element.
How are all compounds joined together?
All compounds are chemically joined together by bonds.
What forces are there in covalent bonds?
There are strong forces attraction in a water molecule. However, there are also weak forces of attraction between molecules - intermolecular forces.
How can intermolecular forces be overcome?
Weak intermolecular forces can be overcome by simply turning liquid water into a gas.
Why do small, simple molecules like water have low melting and boiling points?
Because it doesn’t take much energy to overcome the weak intermolecular forces.
What is an electric current?
A flow of charged particles.
Are simple molecules conductive (electricity)?
Simple molecules have no overall charge and so can’t carry and electric current. In a covalent bond, electrons are shared between two atoms. The strong forces between the negatively charged electrons and the positively charged nuclei hold the electrons in place. The electrons cannot flow and so cannot carry a current.
What are monomers?
Small, simple molecules that can be joined in a chain to form a polymer (monomers are usually linked together by covalent bonds).
What is polythene?
A common polymer made of ethane monomers.
How does the length of polymers affect the amount of intermolecular forces?
Polymer molecules can have different lengths. Longer polymers have more intermolecular forces between them. As they have more weak intermolecular forces, it takes longer to overcome them, which increases the melting and boiling points.
What are molecules?
Groups of atoms joined by covalent bonds.
What are allotropes?
Different structural forms of the same element.
Describe ‘fullerenes’?
Simple molecules where each carbon atom is covalently bonded to three other carbon atoms. They are often tubular molecules (nanotubes) or spherical. Fullerenes have weak intermolecular forces between the molecules and so have low melting points. These weak forces also make them soft and slippery. However, they are very strong due to their covalent bonding.
Describe ‘graphene’?
Graphene is similar to fullerenes but is not a simple molecule. It consists of a sheet of carbon atoms with no fixed formula. The sheet is just one atom thick, making it the lightest known material, but it’s covalent bonds make it extremely strong. It also allows free electrons to move across its surface and so is a good electrical conductor.
Describe ‘diamond’?
- It is a covalent, giant molecular structure, which has huge three-dimensional networks of carbon atoms linked by covalent bonds.
- It also has a high melting point because of the many strong covalent bonds that need to be broken to melt the solid.
- It has four covalent bonds for each carbon atom.
- It is also very hard because it has a rigid network of carbon atoms in a tetrahedral arrangement, joined by strong covalent bonds. This makes diamond useful to cut things.
- It is an electrical insulator because it has no free charged particles.
Describe ‘graphite’?
- It is a covalent, giant molecular structure, which has huge three-dimensional networks of carbon atoms linked by covalent bonds.
- It also has a high melting point because of the many strong covalent bonds that need to be broken to melt the solid.
- It has three covalent bonds for each carbon atom.
- It has a layered structure and means that not all of its electrons are held in covalent bonds.
- It has delocalized electrons which are free to move and can carry an electrical current. This makes it able to conduct electricity well and it is cheap and not very reactive.
- The sheets of carbon in graphite are held together by weak forces of attraction which allow layers to slide past each other, which makes it quite soft and useful as a lubricant.
What are delocalized electrons?
Electrons that are free to move and can carry an electrical current.
What do chemists classify elements into?
Metals and non-metals.
