9. Covalent Bonding
Formation of Covalent Bonds
Dot and Cross Diagrams
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Simple Molecular Structure
Physical Properties of Simple Molecules
Giant Molecular Structure
Physical Properties of Diamond
Physical Properties of Graphite
- Formed between non-metal atoms
- A covalent bond is a pair of shared electrons between two non-metal atoms
Dot and Cross Diagrams
Check
- whether question asks for outermost electrons or all the electrons
- that there are different symbols for the electrons in different atoms
- that there are 8 electrons in the outermost shell after bonding except for H, Li and Be which will have 2 electrons
Simple Molecular Structure
- There are strong covalent bonds between atoms with weak intermolecular forces of attraction between molecules.
Physical Properties of Simple Molecules
- Low melting point and boiling point: Little amount of energy required to break weak intermolecular forces of attraction between the molecules.
- Exist as volatile liquids or gases at r.t.p: Little amount of energy required to break weak intermolecular forces of attraction between the molecules.
- Do not conduct electricity in all states: It exists as molecules and therefore, there are no free moving ions or electrons to conduct electricity.
- Insoluble in water but soluble in organic solvents.
Giant Molecular Structure
- There are strong covalent bonds between atoms throughout the structure. Exception: Graphite has weak intermolecular forces of attraction between the layers.
- For diamond: Each carbon atom is covalently bonded to four other carbon atoms in a tetrahedral arrangement in a giant covalent structure.
- For graphite: Each carbon atom is covalently bonded to three other carbon atoms hexagonal rings in layers. The layers are held by weak intermolecular forces of attraction.
Physical Properties of Diamond
- Very high melting point and boiling point: A lot of energy is required to break all the strong covalent bonds between the carbon atoms throughout the giant covalent structure.
- Do not conduct electricity in all states: All four electrons of each carbon atom are used for bonding and therefore, there are no free moving electrons to conduct electricity.
- Diamond is a very hard solid: A lot of energy is required to break all the strong covalent bonds between the carbon atoms throughout the giant covalent structure.
- Insoluble in both organic solvents and water.
Physical Properties of Graphite
- Very high melting point and boiling point: A lot of energy is required to break all the strong covalent bonds between the carbon atoms throughout the giant covalent structure.
- Can conduct electricity: Only three out of four valence electrons of each carbon atom are used for bonding and therefore, the remaining electrons are delocalised and are free to move within the layers to conduct electricity.
- Graphite is soft and slippery; thus is used as a lubricant: There are weak intermolecular forces of attraction between the layers of hexagonal rings of carbon atoms. When a force is applied, the layers are able to slide past each other.
- Insoluble in both organic solvents and water.