Ionic Bonding and Structure
- Ionic bonds are present in compounds consisting of a metal and a non-metal.
- Electrons are transferred from the metal atom to the non-metal atom.
- Oppositely charged ions are formed which are bonded together by electrostatic attraction.
- Each ion attracts oppositely charged ions from all directions.
- Each ion is surrounded by oppositely charged ions.
- The ions attract each other, forming a giant ionic lattice.
Properties of Ionic Compounds
High Melting Point and Boiling Point
- A large amount of energy is needed to break the strong electrostatic forces that hold the oppositely charged ions together in the solid lattice.
- In a solid lattice the ions are in a fixed position and no ions can move, the ionic compound is a non-conductor of electricity.
- When an ionic compound is melted or dissolved in water, the solid lattice breaks down and the ions are free to move. The ionic compound is now a conductor of electricity.
- The ionic lattice dissolves in polar solvents, such as water.
- The polar water molecules break down the lattice by surrounding each ion to form a solution.
Covalent Bonding and Simple Molecular Structures
- Covalent bonding occurs in compounds consisting of non-metals.
- An electron pair occupies the space between the two atoms' nuclei.
- The negatively charged electrons are attracted to the positive charge of both nuclei.
- This attraction overcomes the repulsion between the two positively charged nuclei.
- Two electrons are shared.
- In a dative covalent bond, one of the atoms supplies both the shared electrons to the covalent bond.
Simple Molecular Structures
- In a solid simple molecular lattice, molecules are held together by weak forces between molecules and the atoms within each molecule are bonded strongly together by covalent bonds.
Properties of Simple Molecular Structures
Low Melting and Boiling Point
- Simple molecular structures have low melting and boiling points because the intermolecular forces are weak van der Waals' forces, so a relatively small amount of energy is needed to break them.
- Simple molecular structures are non-conductors of electricity because there are no charged particles free to move.
- Simple molecular structures are soluble in non-polar solvents. This is because van der Waals' forces form between the simple molecular structure and the non-polar solvent.
- The formation of these van der Waals' forces weakens the lattice structure
Properties of Giant Covalent Structures
High Melting and Boiling Point
- Giant covalent structures have high melting and boiling points because high temperatures are needed to break the strong covalent bonds in the lattice.
- Giant covalent structures are non-conductors of electricity because there are no free charged particles except in graphite.
- Giant covalent structures are insoluble in both polar and non-polar solvents because the covalent bonds in the lattice are too strong to be broken by either polar or non-polar solvents.
Giant Covalent Structures: Diamond
- Tetrahedral structure held together by strong covalent bonds throughout lattice.
- Poor conductivity
- There are no delocalised electrons as all outer-shell electrons are used for covalent bonds
- Tetrahedral shape allows external forces to be spread throughout the lattice
Giant Covalent Structures: Graphite
- Strong hexagonal layer structure, but with weak van der Waals' forces between the layers
- Good conductivity
- There are delocalised electrons between layers
- Electrons are free to move parallel to the layers when a voltage is applied
- Bonding within each layer is strong
- Weak forces between layers allow layer to slide easily
Metallic Bonding and Structure
- The atoms in a solid metal are held together by metallic bonding
- The atoms are ionised
- Positive ions occupy fixed positions in a lattice
- The outer-shell electrons are delocalised
- In a giant metallic lattice the delocalised electrons are spread throughout the metallic structure
- These electrons are able to move within the structure
Properties of Giant Metallic Lattices
High Melting and Boiling Points
- The electrons are free to move throughout the structure, but the positive ions remain where they are
- The attraction between the positive ions and negative delocalised electrons is strong
- High temperatures are needed to break the metallic bonds and dislodge the ions from their rigid positions within the lattice
Good Electrical Conductivity
- The delocalised electrons can move freely anywhere within the metallic lattice
- This allows the metal to conduct electricity, even in the solid state