1.2 Bonding, structure and properties of matter

• What is ionic bonding?


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


  It is a relatively strong attraction between 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?


  Ionic substances 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 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).
  • 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?


  Intermolecular forces 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 due to delocalised electrons.
  • Malleable and soft; layers of atoms 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?


  The simple model 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.
• At what temperature will a pure substance melt or boil?


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


  The three states of matter are solid, liquid, and gas.
• What is nanoscience?


  Nanoscience is the study of particles that are 1 - 100 nm in size.
• What are 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 (soot): 100-2500 nm diameter.
  • Coarse particles (dust): 2500-10,000 nm diameter.
• Why do nanoparticles have different properties compared to bulk materials?


  They have a high surface area to volume ratio.
• What are simple molecular substances made up of?

  Molecules containing a few atoms joined by covalent bonds
• What is the molecular formula for hydrogen?


  H2
• Why do hydrogen atoms often share electrons?

  To complete their outer shell of electrons
• What is the molecular formula for chlorine?

  Cl2
• How many electrons does each chlorine atom need to complete its outer shell?

  One more electron
• What is the molecular formula for oxygen?

  O2
• How many electrons does each oxygen atom need to complete its outer shell?

  Two more electrons
• What is the molecular formula for nitrogen?

  N₂
• How many electrons does each nitrogen atom need to complete its outer shell?

  Three more electrons
• What is the molecular formula for hydrogen chloride?


  HCl
• How is hydrogen chloride similar to H₂ and Cl₂?

  It involves sharing electrons to achieve stable outer shells
• What are the properties of simple molecular substances?

  1. Atoms within molecules are held by strong covalent bonds.
  2. Weak intermolecular forces lead to low melting and boiling points.
  3. Most are gases or liquids at room temperature.
  4. Larger molecules have stronger intermolecular forces and higher melting/boiling points.
  5. They do not conduct electricity due to lack of free electrons or ions.
• What is the reason for low melting and boiling points in simple molecular substances?

  Weak intermolecular forces need to be broken, not covalent bonds
• What happens to the melting and boiling points as molecules get bigger?

  The melting and boiling points increase due to stronger intermolecular forces
• Why do molecular compounds not conduct electricity?

  They are uncharged and lack free electrons or ions
• What is covalent bonding?

  • Involves sharing electrons between atoms.
  • Creates strong covalent bonds within molecules.
• What is the molecular formula for methane?


  CH₄