02- bonding, structure and the props of matter

• What is ionic bonding?

  Electrostatic attraction between positive and negative ions
• Why is ionic bonding considered a strong attraction?

  Due to strong electrostatic forces between ions
• What are the properties of ionic substances?

  • High melting and boiling points
  • Do not conduct electricity when solid
  • Conduct electricity when molten or dissolved

  
• Why do ionic substances not conduct electricity when solid?

  Because ions are in fixed positions
• How do ionic substances conduct electricity when molten or dissolved?

  Ions are free to move in these states
• How are ionic compounds held together?

  • Held in a giant lattice structure
  • Regular structure extending in all directions
  • Electrostatic attraction between ions
• What is important when working out a formula of an ionic compound?

  Positive and negative charges must balance
• How are ionic compounds formed? Explain using MgO as an example.

  • Reaction of a metal with a non-metal
  • Electron transfer occurs
  • Mg gives away 2 electrons to O
  • Mg becomes Mg2+, O becomes O2−
• 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

  
• What is a covalent bond?

  A shared pair of electrons between two atoms
• How do intermolecular forces change as the mass of the molecule increases?

  They increase, raising melting/boiling points
• What are giant covalent substances? Give examples.

  • Solids with atoms covalently bonded in a lattice
  • High melting/boiling points due to strong bonds
  • Mostly do not conduct electricity
  • Examples: Diamond, graphite, silicon dioxide

  
• What are polymers and thermosoftening polymers?

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

  • Diamond: hard, high melting point, no conductivity
  • Graphite: soft, high melting point, conducts electricity
  • Fullerenes: hollow molecules, based on hexagonal rings
  • Nanotubes: cylindrical, high tensile strength, conductive
  • Graphene: single layer of graphite
• 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
  • Different atom sizes distort layers, preventing sliding
• What is metallic bonding?

  Attraction between delocalised electrons and metal ions
• What does the amount of energy needed to change state depend on?

  Strength of forces between particles
• What are the limitations of the simple model of particles?

  No forces between spheres; not true for atoms
• At what temperature does a pure substance melt or boil?

  At a fixed temperature
• What are the three states of matter?

  Solid, liquid, and gas
• What are 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