Chemistry

• What is ionic bonding?

  Ionic bonding is the electrostatic attraction between positive and negative ions.
• Why is ionic bonding considered a strong attraction?


  Because it involves the electrostatic forces between oppositely charged ions.
• How are ionic compounds held together?


  • They are held together in a giant lattice.
  • It’s a regular structure that extends in all directions.
  • Electrostatic attraction between positive and negative ions holds the structure together.
• What are the properties of ionic substances?


  They have high melting and boiling points, do not conduct electricity when solid, and conduct when molten or dissolved in water.
• What is important when working out a formula of an ionic compound?


  Ionic compounds are electrically neutral, meaning positive and negative charges balance each other.
• How are ionic compounds formed? Explain using MgO as an example.


  • Reaction of a metal with a non-metal.
  • Electron transfer occurs; metal gives away outer shell electrons to non-metal.
  • Mg becomes Mg²⁺ and O becomes O^2- (oxide).
• What is a covalent bond?


  A covalent bond is 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 lead to low melting and boiling points.
• How do intermolecular forces change as the mass/size of the molecule increases?


  They increase, causing melting and boiling points to increase as well.
• What are polymers and thermosoftening polymers?


  • Polymers are very large molecules with atoms linked by covalent bonds.
  • Thermosoftening polymers melt/soften when heated due to no bonds between polymer chains.
• What are giant covalent substances? Give examples.


  • Solids with atoms covalently bonded in a giant lattice.
  • High melting/boiling points due to strong covalent bonds.
  • Examples: Diamond, graphite, silicon dioxide.
• Describe and explain the properties of allotropes of carbon.


  • Diamond: Hard, high melting point, does not conduct electricity.
  • Graphite: Soft, high melting point, conducts electricity due to delocalised electrons.
  • Fullerenes: Hollow molecules based on hexagonal rings.
  • Nanotubes: High tensile strength and conductivity.
  • Graphene: A single layer of graphite.
• What is metallic bonding?


  Metallic bonding is the attraction between delocalised electrons and the nuclei of metal ions.
• Describe properties of metals.


  • High melting/boiling points due to strong forces of attraction.
  • Good conductors of heat and electricity (delocalised electrons).
  • Malleable and soft (layers can slide over each other).
• What are alloys and why are they harder than pure metals?


  • Alloys are mixtures of metals with other elements.
  • Different sizes of atoms distort layers, preventing them from sliding over each other, making alloys harder.
• What are the limitations of the simple model of bonding?


  It does not account for forces between spheres and assumes atoms, molecules, and ions are solid spheres.
• What does the amount of energy needed to change state depend on?


  It depends on the strength of the forces between the particles of the substance.
• A pure substance will melt or boil at what temperature?


  A pure substance will melt or boil at a fixed temperature.
• What are the three states of matter?

  Solid, liquid, and gas.
• What is nanoscience?


  Nanoscience is the study of particles that are 1 - 100 nm in size.
• State the uses of nanoparticles.


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


  • Fine particles: 100-2500 nm diameter.
  • Coarse particles: 2500-10000 nm diameter.
• Why do nanoparticles have properties different from those for the same materials in bulk?


  Because they have a high surface area to volume ratio.