Topic 2 - Bonding, Structure and the properties of Matter

• 1. What is ionic bonding?


  Ionic bonding is the electrostatic attraction between positive and negative ions. 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 in a substance. Electrostatic attraction between positive and negative ions holds the structure together.
• State properties of ionic substances?


  High melting and boiling point (strong electrostatic forces between oppositely charged ions). Do not conduct electricity when solid ( ions in fixed positions). Conduct when molten or dissolved in water - ions are free to move.
• Give 5 examples of positive ions and 5 examples of negative ions. What is important when working out a formula of an ionic compound?

  Positive ions: Sodium (Na+), Potassium (K+), Calcium (Ca2+), Magnesium (Mg2+), Iron (Fe3+) Negative ions: Chloride (Cl-), Sulfate (SO4^2-), Nitrate (NO3-), Oxide (O2-), Hydroxide (OH-) Important when working out a formula of an ionic compound: Balancing the charges of the positive and negative ions to achieve overall neutrality.
• 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 is in Group 2, so has 2 available outer shell electrons. O is in group 4, so can accept 2 electrons to get a full outer shell configuration. Mg becomes Mg2+ and O becomes O2- (oxide )
• What is a covalent bond?

  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 therefore, low melting and boiling points.
• How do intermolecular forces change as the mass/size of the molecule increases?

  They increase. That causes melting/boiling points to increase as well (more energy needed to overcome these forces).
• What are polymers? What are thermosoftening polymers?

  Polymers are very large molecules with atoms linked by covalent bonds. Thermosoftening polymers - special type of polymers; they melt/soften when heated. There are no bonds between polymer chains. Strong intermolecular forces ensure that the structure is solid at room temperature. These forces are overcome with heating - polymer melts.
• What are gaint covalent substances? Give examples

  Solids, atoms covalently bonded together in a giant lattice. High melting/boiling points - strong covalent bonds. Mostly don't conduct electricity ( no delocalised e- ). Diamond, graphite, silicon dioxide.
• Describe and explain the properties of Diamond

  four, strong covalent bonds for each carbon atom

  very hard (strong bonds) very high melting point (strong bonds) does not conduct ( no delocalised electrons ).
• Describe and explain the properties of Graphite

  three colavent bonds for each carbon atom

  layers of hexagonal rings

  high melting point
• Describe and explain the properties of Fullerenes

  hollow shaped molecules

  based on hexagonal rings but may have 5/7 carbon rings

  c60 has a spherical shape, simple molecular structure (buckminsterfullerene)
• Describe and explain the properties of Nanotubes


  cylindrical fullerene with high length to diameter ratio

  high tensile strength (strong bonds)

  conductivity ( delocalised electrons)
• Describe and explain the properties of Graphene

  a single layer of graphite
• What is metallic bonding


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


  high melting/boiling points ( strong forces of attraction )

  good conductors of heat and electricity ( delocalised electrons )

  malleable, soft ( layers of atoms can slide over each other whilst maintaining the attraction forces )
• What are alloys? why are they harder than pure metals?

  Alloys:

  mixtures of metal with other elements, usually metals

  different sizes of atoms distorts the layers, so they can't slide over each other, therefore alloys are harder than pure metals.
• What are the limitations of the simple model?

  There are no forces between spheres and atoms, molecules and ions are solid spheres - this is not true
• What does the amount of energy needed to change state from solid to liquid or liquid to gas depend on?

  The strength of the forces between the particles of the substance. The nature of the particles involved depends on the type of bonding and the structure of the substance. The stronger the forces between the particles the higher the melting point and boiling point of this substance.
• A pure substance will melt or boil at...?

  A fixed temperature.

  A mixture will melt over a range of temperatures
• What is nanoscience?

  Science that studies particles that are 1 - 100nm in size.
• State the uses of nanoparticles

  Medicine (drug delivery systems)

  Electronics

  Deodorants

  Sun creams ( better skin coverage and more effective protection against cell damage )
• What are fine and coarse particles?

  Fine particles (soot), 100-2500 nm diameter

  Coarse particles (dust), 2500-1000000 nm in diamter
• Why do nanoparticles have properties different from those of the same materials in bulk?


  High surface area to volume ratio
• Explain why methane and poly(ethene) exist in different states at room temperature

  methane has much smaller molecules so has weaker intermolecular forces which require less energy to overcome. Therefore having a lower melting/boiling point.
• suggest why alloys do not conduct electricity as well as pure metals

  alloys have different sized atoms

  the movement of electrons is restricted