8 Questions
What is the main difference in the structure between simple molecular and giant covalent structures?
Simple molecular structures consist of many small molecules held together by weak intermolecular forces, whereas giant covalent structures are made up of all atoms covalently bound in a giant 3D structure.
Why do ionic compounds have high melting and boiling points?
Ionic compounds have high melting and boiling points due to the strong electrostatic attractions between oppositely charged ions.
What is the reason for the brittleness of ionic compounds?
The brittleness of ionic compounds is due to the repulsion between ions of the same charge when the crystal is distorted.
Why do giant covalent structures have very high melting and boiling points?
Giant covalent structures have very high melting and boiling points because strong covalent bonds must be broken, requiring a significant amount of energy.
What is the unique feature of graphite that allows it to conduct electricity?
The delocalised electrons between the layers of carbon atoms in graphite allow it to conduct electricity.
What is the difference between the structure of graphite and diamond?
Graphite has a layered structure with weak interlayer attractions, whereas diamond has a giant 3D structure with all atoms covalently bound.
What is the definition of an allotrope?
An allotrope is a form of an element that exists in the same state (solid, liquid, or gas) but has different properties due to its atoms being arranged differently.
What is the basis of metallic bonding?
Metallic bonding is based on the electrostatic attraction between the positive ions and the delocalised electrons.
Study Notes
Giant Ionic Lattices
- Ionic crystals have a 3D structure held together by the attraction between oppositely charged ions.
- High melting/boiling points are due to many strong electrostatic attractions between oppositely charged ions.
- Melting/boiling point increases with increasing charge on ions (stronger attraction between +2 / -2 charges than +1 / -1).
- Ionic compounds are brittle, as crystal distortion puts ions of the same charge next to each other, leading to repulsion and splitting of the crystal.
- They do not conduct electricity in solid state (ions are fixed in position) but do conduct electricity in solution/molten state (ions are free to move).
Covalent Structures
Simple Molecular
- Consist of lots of small molecules held together by weak intermolecular forces.
- Very strong covalent bonds within molecules are not broken.
- Low melting/boiling points due to easily overcomable weak intermolecular forces (often gases at room temperature).
Giant Covalent
- All atoms are covalently bound in a giant 3D structure.
- Very high melting/boiling points due to strong bonds that must be broken.
- Do not conduct electricity (no delocalised electrons to conduct electricity).
Graphite
- Unusual covalent structure with weak interlayer attractions, allowing layers of carbon atoms to easily slide over one another, making it soft.
- Delocalised electrons between layers move, allowing graphite to conduct electricity.
Allotropes
- Forms of an element that exist in the same state (solid, liquid, or gas) but have different properties due to different atomic arrangements.
- Examples: graphite, diamond, and buckminster fullerene are allotropes of carbon.
Metallic Bonding
- The electrostatic attraction between positive ions and delocalised electrons.
- Metals exist as a giant structure of positive ions surrounded by a sea of delocalised electrons.
- Good conductors of electricity due to free movement of delocalised electrons through the lattice structure.
- Malleable as layers of ions slide over each other.
- High melting/boiling points due to the strong electrostatic attraction between positive ions and delocalised electrons.
Alloys
- A mixture of a metal with one or more other elements (metal or nonmetal).
- Different sized particles in an alloy distort the layers within the structure, making them less malleable.
- No layers can slide, reducing malleability.
Learn about the structure and properties of ionic compounds, including their high melting and boiling points, brittleness, and how they are held together by electrostatic attractions.
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