PMT

• 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
  • Do not conduct electricity when solid
  • Conduct when molten or dissolved in water
• 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.

  • Reaction of a metal with a non-metal
  • Electron transfer occurs
  • Mg gives away 2 electrons to O
  • Mg becomes Mg2+ and O becomes O2−
• 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: hard, high melting point, does not conduct
  • Graphite: soft, high melting point, conducts electricity
  • Fullerenes: hollow molecules, based on hexagonal rings
  • Nanotubes: high tensile strength, conductive
• 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?

  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
• What is nanoscience?

  Study of particles 1 - 100 nm in size
• State the uses of nanoparticles.

  • Medicine (drug delivery systems)
  • Electronics
  • Deodorants
  • Sun creams (better skin coverage)
• What are fine and coarse particles?

  Fine: 100-2500 nm; Coarse: 2500-10000 nm
• Why do nanoparticles have different properties than bulk materials?

  High surface area to volume ratio