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.

HHincomplete outer shells

HHboth atoms have a

full outer shellsolid lineH H–

–H H

Remember more than one pair of electrons can be shared.

Draw the molecules in both ways (only the outer shell)

Carbon

Oxygen

Hydrogen

Chlorine

Nitrogen

H

Cl

N

O

C

Chlorine (2.8.7) needs 1 more electron to have a completely full outer shell.

ClCl

Cl2 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.

O2 or O=O

To achieve this, it can share two electrons with another oxygen atom. This creates a double bond.

O OO

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.

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

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

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: covalent thermosetting tangled 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.