Electrons, Bonding and Structure
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- Created by: megantiffin
- Created on: 15-02-16 13:22
Ionic Bonding and Structure
Ionic Bonding
- 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.
Ionic Structure
- 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.
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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.
Electrical Conductivity
- 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.
Solubility
- 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.
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Covalent Bonding and Simple Molecular Structures
Covalent Bonding
- 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.
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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.
Electrical Conductivity
- Simple molecular structures are non-conductors of electricity because there are no charged particles free to move.
Solubility
- 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
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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.
Electrical Conductivity
- Giant covalent structures are non-conductors of electricity because there are no free charged particles except in graphite.
Solubility
- 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.
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Giant Covalent Structures: Diamond
Structure
- Tetrahedral structure held together by strong covalent bonds throughout lattice.
Electrical Conductivity
- Poor conductivity
- There are no delocalised electrons as all outer-shell electrons are used for covalent bonds
Hardness
- Hard
- Tetrahedral shape allows external forces to be spread throughout the lattice
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Giant Covalent Structures: Graphite
Structure
- Strong hexagonal layer structure, but with weak van der Waals' forces between the layers
Electrical Conductivity
- Good conductivity
- There are delocalised electrons between layers
- Electrons are free to move parallel to the layers when a voltage is applied
Hardness
- Soft
- Bonding within each layer is strong
- Weak forces between layers allow layer to slide easily
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Metallic Bonding and Structure
Metallic Bonding
- 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
Metallic Structure
- In a giant metallic lattice the delocalised electrons are spread throughout the metallic structure
- These electrons are able to move within the structure
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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
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