C2 - Covalent Substances Flashcards
How do you draw a dot and cross diagram for covalent bonding?
Draw a Venn diagram
Only draw the outer shells unless question asks otherwise
Put dots on one atom and crosses on the other
Put the required amount of the those dots and crosses in the overlap so that both atoms have a full outer shell
Describe covalent bonding
Non-metals share electrons in their outer shells
This means that both atoms feel that they have a full outer shell
They are held together because the shared electrons are attracted by both nuclei
What are simple covalent substances?
Where small covalently bonded compounds are held together by very weak intermolecular forces
What happens when simple covalent substances melt or boil?
The intermolecular forces are broken and no harm comes to the covalent bonds
Do simple covalent substances conduct electricity and why?
No
Because there are no freely moving charged particles
What are the melting and boiling points of simple covalent substances like?
Usually gases or liquids at room temperature
What are giant covalent substances?
Covalent structures where all atoms are bonded to each other by strong covalent bonds
What are the 3 properties of giant covalent structures?
High melting and boiling points (strong bonds)
Never conduct electricity (except for graphite)
Describe diamond
Each carbon atom forms four covalent bonds in a very rigid giant covalent structure
This makes diamond the hardest natural substance
Describe graphite
Each carbon atom only forms 3 covalent bonds which creates layers that are free to slide over each other
Each carbon atom has one delocalised electron that is between the layers and holds them together (weak intermolecular forces)
Graphite is soft because the layers are free to slide over each other because of the weak intermolecular forces
Good conductor of electricity and heat because of the delocalised electrons
Describe silicon dioxide
Sometimes called silica and it is what sand is made of
Each grain of sand is one giant structure of silicon and oxygen
Describe metals
Metal atoms lose their outer electrons to their surroundings
If many metal atoms are together, the sea of delocalised electrons is enough to hold the atoms together in a regular structure
What are the 4 properties of metals?
Free electrons allow conduction of heat and electricity
They are strong because of the strong electrostatic attractions between the positive metal ions and negative electrons
The regular arrangement allows layers of atoms to slide over each other allowing metals to be bent and shaped
