topic 2- structure and bonding

• What is ionic bonding?

  Electrostatic attraction between positive and negative ions
• How strong is the attraction in ionic bonding?

  It is a relatively strong attraction
• How are ionic compounds held together?

  • Held together in a giant lattice
  • Regular structure extending in all directions
  • Electrostatic attraction between positive and negative ions
• What are the properties of ionic substances?

  High melting and boiling points

  
• Why do ionic substances not conduct electricity when solid?

  Because ions are in fixed positions
• When do ionic substances conduct electricity?

  When molten or dissolved in water
• What is important when working out a formula of an ionic compound?

  Positive and negative charges must balance
• What is a covalent bond?

  A shared pair of electrons between two atoms
• Describe the structure and properties of simple molecular covalent substances.

  • Do not conduct electricity (no ions)
  • Composed of small molecules
  • Weak intermolecular forces
  • Low melting and boiling points

  
• How do intermolecular forces change as the mass of the molecule increases?

  They increase, raising melting/boiling points
• What are polymers and thermosoftening polymers?

  • Polymers: large molecules linked by covalent bonds
  • Thermosoftening polymers: melt/soften when heated
• Describe and explain the properties of allotropes of carbon.

  Diamond:

  • Four strong covalent bonds
  • Very hard, high melting point
  • Does not conduct electricity

  
  

  Graphite:

  • Three covalent bonds, layers of hexagons
  • High melting point, soft due to weak forces
  • Conducts electricity due to delocalised electrons

  
  

  Fullerenes:

  • Hollow molecules based on hexagonal rings
  • Example: C60 (Buckminsterfullerene)

  
  

  Nanotubes:

  • Cylindrical fullerenes with high strength and conductivity

  
  

  Graphene:

  • A single layer of graphite
• What is metallic bonding?

  Attraction between delocalised electrons and metal ions
• Describe properties of metals.

  • High melting/boiling points
  • Good conductors of heat and electricity
  • Malleable and soft

  
• What are alloys and why are they harder than pure metals?

  • Alloys: mixtures of metals with other elements
  • Harder due to distorted layers preventing sliding
• What are the limitations of the simple model of bonding?

  No forces between spheres; not true for atoms
• What does the amount of energy needed to change state depend on?

  Strength of forces between particles
• A pure substance will melt or boil at what temperature?

  A fixed temperature
• What are the three states of matter?

  Solid, liquid, and gas
• State the uses of nanoparticles.

  • Medicine (drug delivery systems)
  • Electronics
  • Deodorants
  • Sun creams (better skin coverage)
• Why do nanoparticles have different properties than bulk materials?

  High surface area to volume ratio