 Why don’t we use lead in pencils?  What is special about the graphite that is used?

 Graphite is a giant covalent structure  Can you remember what a covalent bond looks like?

When non-metal atoms react together, they need to gain electrons to fill their outer shell and become stable. They can only do this if they share electrons with each other. The atoms share electrons so there is a strong force that joins the atoms together. This is called a covalent bond. H H incomplete outer shells H H both atoms have a full outer shell solid line HH – – HH

Remember more than one pair of electrons can be shared. Draw the molecules in both ways (only the outer shell)

Chlorine (2.8.7) needs 1 more electron to have a completely full outer shell. Cl Cl 2 or Cl–Cl To achieve this, it can share an electron with another chlorine atom. This creates a single bond. Cl

O Oxygen (2.8.6) needs 2 more electrons to have a completely full outer shell. O 2 or O=O To achieve this, it can share two electrons with another oxygen atom. This creates a double bond. O O O

Graphite is a common form of carbon in which each atom is covalently bonded to three others, leaving one free bond. This forms rings of six atoms, creating a giant structure containing many layers. These layers are held together by weak forces of attraction. C C C C weak forces of attraction

 Graphite has free electrons within its structure (delocalised electrons)  These allow it to conduct electricity  Graphite layers slide over each other easily so can reduce friction  Graphite is used in pencils (the hardness is altered by changing the clay and graphite ratio)

 Plastics are also made from covalently bonded compounds  Can you remember the 2 different types of plastic from Core Science?  Make a list of any common household items that are made of plastics

 HDPE (High Density PE) › Bottles (biggest application) › milk bottles (largest bottle sector)  LDPE (low Density PE) › Supermarket carrier bags › Packaging film (eg. cling film) › Washing up liquid bottles

Think of the properties that the polymer needs for its function and relate this to the facts we have just discussed.

 Complete the following paragraph: covalentthermosettingtangled cross links The polymer chains in a thermosoftening polymer form a ______ web. The polymer softens at relatively low temperatures. Other polymers have strong _______ bonds between their chains which form _______. We call these _______ polymers.