What are the properties of simple covalent structures?
- Usually gases or liquids at room temperature (if solid, they are soft solids)
- Low melting and boiling points
- Do not conduct electricity
Why do covalent structures have low melting and boiling points?
The covalent bonds within the molecules are strong but the intermolecular forces are weak and easy to break.
Why do covalent structures not conduct electricity?
The strong forces between the negatively charged electrons and the positively charge nuclei hold the shared electrons in place. The electrons cannot flow so cannot carry a current.
What is a polymer?
A long chain molecule made from many monomers joined together.
What is a monomer?
Small molecules that join together by covalent bonds.
Why do longer polymers have higher melting and boiling points than shorter ones?
Longer polymers have more intermolecular forces between them.
What are molecules?
Groups of atoms joined by covalent bonds. They can be compounds or elements.
What are allotropes?
Different structural forms of the same element.
What are the 4 allotropes of carbon?
- Graphite
- Fullerene
- Graphene
- Diamond
Which allotropes of carbon have a covalent, giant molecular structure?
- Graphite
- Graphene
- Diamond
What are the characteristics of graphite?
- Giant molecular structure
- Layered structure
- High melting and boiling points (strong covalent bonds)
- Three covalent bonds for each carbon atom
- Good conductor of electricity (delocalised electrons)
- Soft and useful as a lubricant (weak intermolecular forces allow layers to slide past each other)
What are the characteristics of fullerenes?
- Simple molecular structure
- Often tubular or spherical
- Low melting and boiling points (weak intermolecular forces)
- Three covalent bonds for each carbon atom
- Soft and slippery (weak intermolecular forces)
What are the characteristics of graphene?
- Giant molecular structure
- One atom thick sheet (lightest known material)
- High melting and boiling points (strong covalent bonds)
- Three covalent bonds for each carbon atom
- Good conductor of electricity (delocalised electrons)
- Extremely strong (covalent bonds)
What are the characteristics of diamonds?
- Giant molecular structure
- Tetrahedral arrangement
- High melting and boiling points (strong covalent bonds)
- Four covalent bonds for each carbon atom
- Bad conductor of electricity (no delocalised electrons)
- Extremely hard and used for cutting tools (rigid network of carbon atoms in a tetrahedral arrangement)
What are the properties of metals?
- Solids with high melting points
- Shiny (when polished)
- Malleable
- High density
- Good conductors of electricity
What is the structure of metals?
Atoms in a metallic element are all the same size and packed closely together in layers to form a giant lattice. Atoms have 1-3 electrons in outer shell which are lost from each atom and become free to move, creating a giant lattice of positive metal ions surrounded by a ‘sea’ of delocalised electrons.
What is metallic bonding?
The electrostatic forces of attraction between the positive metal ions and the negative delocalised electrons. This attraction is strong so metals have high melting and boiling points.
Why are metals malleable?
Layers of ions slide over each other and the ‘sea’ of electrons hold the ions together so the metal changes shape instead of breaking.
Why are metals good conductors of electricity?
When a potential difference (voltage) is applied between two points on a piece of metal, the delocalised electrons will flow towards the positive side. This flow of electrons transfers energy and forms an electrical current. The conductivity increases as the number of delocalised electrons increases.
What are the characteristics of metallic bonding?
- Positive ions surrounded by a ‘sea’ of delocalised electrons
- Strong attraction between ions and delocalised electrons
- High melting points (almost all solids at room temp)
- Conduct electricity
E.g. sodium
What are the characteristics of a giant ionic structure?
- Regular 3D arrangement of positive and negative ions
- Strong electrostatic attraction between positive and negative ions
- High melting points (always solid at room temp)
- Only conduct electricity when molten/dissolved in solution
E.g. sodium chloride
What are the characteristics of a simple covalent structure?
- Isolated molecules with weak intermolecular forces
- Strong covalent bonds (shared electrons)
- Low melting points (gases and liquids at room temp)
- Don’t conduct electricity
E.g. iodine
What are the characteristics of a giant covalent structure?
- Repeating 3D structure
- Strong covalent bonds (shared electrons)
- High melting points (always solid at room temp)
- Most don’t conduct electricity (except graphite)
E.g. Diamond
Why were bonding models created?
Scientists developed them to explain how different types of bonds and structures are formed. They also help explain the properties of different substances.
