topic 2 - bonding, structure and the properties of matter

• What is ionic bonding?

  Ionic bonding is the 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?

  • 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?

  High melting and boiling points, do not conduct electricity when solid, conduct when molten or dissolved in water.

  
• Give an example of a positive ion.

  Na+
• Give an example of a negative ion.

  Cl−
• 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 in terms of MgO case.

  • Reaction of a metal with a non-metal.
  • Electron transfer occurs; metal gives away its outer shell electrons to non-metal.
  • Mg becomes Mg2+ and O becomes O2− (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).
  • Small molecules.
  • Weak intermolecular forces, leading to low melting and boiling points.

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

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

  Forces of attraction between delocalised electrons and nuclei of metal ions.
• Describe properties of metals.

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

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

  There are no forces between spheres, and atoms, molecules, and ions are treated as solid spheres, which is not true.
• 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 fixed temperature.
• What are the three states of matter?

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

  Science that studies 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 more effective 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?

  They have a high surface area to volume ratio.