Bonding & structure

• A covalent bond forms when electrons from both atoms share an orbital to form a shared pair of electrons
• The strength of the bond between two atoms is called their bond enthalpy.
• Covalent bonds are strong because the electron pairs are held between two nuclei by electrostatic forces.
• The strength of a covalent bond depends on how many electrons are being shared - more is stronger
• Suggest two reasons why 9 carat gold is often used instead of pure gold to make jewellery.

  Cost

  Pure gold is soft
• State one reaction condition that can be changed when making poly(ethene).

  Pressure
• What are the bonds between atoms in graphene?

  Covalent
• Graphite is used in pencils. Explain why

  Layers can slip as there’s no bonds between layers
• Explain why metals can be shaped.

  Made of layers which can slide over each other
• Copper metal is used in electrical appliances. Describe the bonding in a metal, and explain why metals conduct electricity.

   

  Lattice of positive ions with delocalised electron and electrostatic forces of attraction between the positive ions and the electrons which can move through the structure and carry charge
• This question is about sodium chloride and iodine. Describe the structure and bonding in sodium chloride.

  Giant lattice which is ionic and has electrostatic attraction. Na+ and Cl
• Explain why iodine has a low melting point.

  Simple molecules with intermolecular forces which are weak
• Explain, in terms of particles, why liquid iodine does not conduct electricity

  Iodine has no delocalised ion so can’t carry charge
• Aluminium ions move to the negative electrode. Explain why.

  Aluminium ions are positive so they’re attracted to the negative electrode
• Explain why graphite is very soft

  It has layers which can slide over each other as between the layers there are only weak forces
• Explain why diamond is very hard

  As each atom forms four bonds and covalent bonds are strong
• Colbalt oxide is a better catalyst than colbalt oxide powder (why)

  They have high Sa to V ratio
• How is the size of nanoparticles different from normal-sized particles?

  Nanoparticles are smaller