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How do non-metal elements bond together the make molecules & compounds?
Covalent bonding
Covalent bonding is the sharing ofd electrons. This is between two non-metal atoms and forms a full outer shell of electrons. We draw this using dot and cross diagrams with overlapping electron shells.
You must be able to draw dot and cross diagrams for molecules containing single and multiple bonds.
Single bond (2 electrons shared; 1 from each atom)
Double bond (4 electrons shared; 2 from each atom)
Rules
If one atom shares one electron with the atom next to it that atom must share the same back.
After counting up all the original electrons and the extra electrons from the sharing, all atoms must have a full outer shell.
Simple molecular substances
simple molecular substances are made up of molecules.
(A molecule is a collection of atoms joined together by covalent bonds, e.g. CO2, H2O and O2).
The molecules are held together by weak intermolecular
forces.
Boiling and melting point
To melt and boil a simple molecular substance (turn from a solid to a gas) you have to break the weak intermolecular forces that hold the molecules together as a solid.
These forces are weak so simple molecule substances have low boiling and melting points.
Electrical conductivity
Simple molecular substances do not conduct electricity!This is because they don't have any free electrons or ions to carry the electrical charge.
Giant Covalent Substances
Giant covalent substances are made up of millions and millions of atoms which are all bonded together with a network of covalent bonds.
Graphite
Silica (SiO2)
Structure
Diamond – Made up of carbon atoms. All carbon atoms covalently bonded to 4 other carbon atoms. These strong covalent bonds make it extremely hard.
Graphite – Made up of layers of carbon atoms. These layers can slide over one another and rub off making graphite soft and good for use in pencils.
Silica – Made up of silicon and oxygen atoms all covalently bonded together. It is very hard.
Melting point and boiling point
All giant covalent molecules have a high melting point and boiling point.
To boil or melt a giant molecular substance you would have to pull the atoms apart.
The atoms are all connected with covalent bonds.
Covalent bonds are strong so need a lot of energy (heat) to break.
Electrical conductivity
Diamond doesn’t conduct electricity because there are no free electrons or ions to carry the charge.
Silica is a poor conductor of electricity.
Graphite is the odd on out. It can conduct electricity because electrons can move within the layers and carry the electrical charge.
Website: Link to BBC Bitesize
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