Bonding, Structure and Properties of Matter

• Ionic bonding is the electrostatic attraction between positive and negative ions. It is a relatively strong attraction
• Ionic compounds are held together in a giant lattice structure that extends in all directions. The structure is held together by the electrostatic attraction between positive and negative ions
• Properties of ionic substances:

  • High melting and boiling point (due to 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)
• Examples of positive ions: Na+, Mg2+, Al3+, Ca2+, Rb+

  Examples of negative ions (anions): Cl−, Br−, SO42−, NO3−, OH− (chloride, bromide, sulfate, nitrate, hydroxide)

  When working out a formula of an ionic compound, it is important to ensure that positive and negative charges balance each other to maintain electrical neutrality
• Ionic compounds are formed through the reaction of a metal with a non-metal. Electron transfer occurs, where the metal gives away its outer shell electrons to the non-metal. For example, in the case of MgO, Mg becomes Mg2+ and O becomes O2− (oxide)
• Covalent bond is a shared pair of electrons between two atoms
• Properties of simple molecular covalent substances:

  • Do not conduct electricity (no ions)
  • Consist of small molecules
  • Have weak intermolecular forces, resulting in low melting and boiling points
• Intermolecular forces increase as the mass/size of the molecule increases. This leads to higher melting/boiling points as more energy is needed to overcome these forces
• Polymers are very large molecules with atoms linked by covalent bonds. Thermosoftening polymers melt/soften when heated due to no bonds between polymer chains. Strong intermolecular forces keep the structure solid at room temperature, but heating overcomes these forces causing the polymer to melt
• Giant covalent substances are solids where atoms are covalently bonded in a giant lattice. They have high melting/boiling points due to strong covalent bonds. They mostly do not conduct electricity. Examples include diamond, graphite, and silicon dioxide
• Allotropes of carbon:

  • Diamond: very hard, high melting point, does not conduct electricity
  • Graphite: layers of hexagonal rings, high melting point, conducts thermal and electricity
  • Fullerenes: hollow shaped molecules, may have 5/7-carbon rings, C60 has a spherical shape
  • Nanotubes: cylindrical fullerene with high tensile strength and conductivity
  • Graphene: a single layer of graphite
• Metallic bonding is the forces of attraction between delocalised electrons and nuclei of metal ions
• Properties of metals:

  • High melting/boiling points
  • Good conductors of heat and electricity
  • Malleable and soft due to layers of atoms that can slide over each other while maintaining attraction forces
• Alloys are mixtures of metal with other elements, usually metals. They are harder than pure metals because different sizes of atoms distort the layers, preventing them from sliding over each other
• The amount of energy needed to change state from solid to liquid or liquid to gas depends 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 the substance
• A pure substance will melt or boil at a fixed temperature, while a mixture will melt over a range of temperatures
• The three states of matter are solid, liquid, and gas
• Nanoscience studies particles that are 1 - 100nm in size
• Uses of nanoparticles:

  • Medicine (drug delivery systems)
  • Electronics
  • Deodorants
  • Sun creams (better skin coverage and more effective protection against cell damage)
• Fine particles (soot) have a diameter of 100-2500 nm, while coarse particles (dust) have a diameter of 2500-105 nm
• Nanoparticles have different properties than those for the same materials in bulk due to their high surface area to volume ratio