Bonding, Structure, and Properties

• What are the main physical properties of metals?

  High melting/boiling points, good electrical/thermal conductors, malleable, ductile, shiny.
• Describe the bonding and structure of an ionic compound.

  Giant lattice of oppositely charged ions held together by strong electrostatic forces.
• Why do simple molecular covalent substances have low melting points?

  They have weak intermolecular forces between molecules that require little energy to break.
• What makes giant covalent substances different from simple covalent molecules?

  Atoms are bonded in a large continuous network, not small separate molecules.
• Explain the ‘sea of electrons’ model in metals.

  Positive metal ions in a lattice are surrounded by delocalised electrons which are free to move.
• Why can metals conduct electricity?

  Delocalised electrons move freely and carry charge through the structure.
• How does ionic bonding occur?

  Electrons are transferred from a metal atom to a non-metal atom, forming oppositely charged ions.
• What does a dot and cross diagram for an ionic compound show?

  Electron transfer, full outer shells, and the charges of ions.
• Why are ionic compounds brittle?

  When layers shift, like charges repel and cause the structure to break.
• How are covalent bonds formed?

  By sharing pairs of electrons between non-metal atoms to achieve full outer shells.
• What do dot and cross diagrams show in covalent bonding?

  Shared electron pairs and bonding between atoms.
• Why don’t simple covalent substances conduct electricity?

  They have no free electrons or ions to carry charge.
• What is the structure of diamond?

  Each carbon atom is bonded to 4 others in a tetrahedral 3D network.
• Why can graphite conduct electricity?

  Each carbon atom bonds to 3 others, leaving 1 delocalised electron per atom.
• What is graphene?

  A single layer of graphite – one atom thick, strong, flexible, excellent conductor.
• What is the key structural difference between diamond and graphite?

  Diamond has 4 bonds per carbon (tetrahedral), graphite has 3 (planar layers).
• Why do fullerenes have unique properties?

  Their spherical/cage-like shape allows them to trap molecules – used in drug delivery.
• What are carbon nanotubes used for?

  Strong, conductive materials used in nanotechnology and electronics.
• Why do nano-sized silver particles have different properties from bulk silver?

  High surface area to volume ratio gives antibacterial properties not seen in bulk.
• Give one use for nano-scale silver.

  Wound dressings, antibacterial sprays, fabrics.
• What property makes nano titanium dioxide useful in sunscreens?

  It blocks UV light and is invisible to the human eye due to small particle size.
• What are the risks of using nanoparticles?

  Unknown health/environment effects; can be absorbed or inhaled easily.
• What are thermochromic pigments used for?

  Mugs, battery indicators – change colour with temperature.
• What do photochromic pigments do?

  Change colour in response to light (used in sunglasses).
• What is a shape memory alloy and give a use?

  Returns to original shape when heated – used in dental braces and glasses frames.