C2.1 Bonding, structure & properties

• Compound


  A substance in which 2 or more elements are chemically combined
• Types of chemical bonds


  • Ionic
  • Metallic
  • Covalent
• Ionic compounds


  • Strong electrostatic attraction between oppositely charged ions means they have high melting and boiling points
  • In solid state, ions are fixed in place so they do not conduct electricity
  • When molten/dissolved, ions can move around so they conduct electricity
  • They are brittle
• Metallic compounds


  • The layers of ions in metals are able to slide over each other, so metals are malleable and ductile
  • The delocalised electrons can move through the metal and carry charge, so metals conduct electricity and heat
  • Metallic bonds are very strong and require large amounts of energy to be broken, giving most metals high melting and boiling points
• Simple molecular covalent substances


  • Have weak intermolecular forces between the molecules, so they have low melting and boiling points
  • Do not conduct electricity because simple molecules do not have an overall charge
  • They are usually gases or liquids
• Smart materials


  Responsive to certain stimuli such as temperature and moisture
• Shape memory alloys and shape memory polymers


  • Can be bent and deformed but return to their original shape when heated
  • Used in sports equipment, such as gum shields and medical stitches
  • Used in car bodies and plates for bone fractures
• Thermochromic materials


  • Change colour when they reach a certain temperature
  • Used in mugs and spoons which change colour when their contents are hot
• Photochromic pigments


  • Change colour when exposed to light
  • Used in sunglasses that darken when in bright sun
• Polymer gels


  • Hydrogels absorb up to 1,000 times their volume in water
  • Certain stimuli (changes in pH and temperature) can cause the water to be released
  • Used in nappies, fake snow and hair gel
• Ionic Bonding


  The transfer of electrons
• Formation of ionic bond

  1. Metal atom loses electrons to form a positively charged ion

  2. Non-metal gains these electrons to form a negatively charged ion
• Ionic bond formation


  • Na + Cl → Na+ + Cl-
• Ionic bond


  The electrostatic charge between oppositely charged ions
• Ionic compounds


  • Form giant ionic lattices with a large number of positive and negative ions
  • Have high melting and boiling points
  • Are strong and require a lot of energy to break
• Ionic compounds


  • Conduct electricity when molten or as part of aqueous solution
• Covalent bond


  Formed when 2 atoms share electrons
• Covalent bond


  The electrostatic charge between the positive nuclei and the shared pair of negative electrons
• Simple covalent molecules


  • Consist of a few atoms joined by covalent bonds
  • Have low melting and boiling points due to weak intermolecular forces
  • Are gases or liquids at room temperature
  • Don't conduct electricity because there are no free electrons or ions
• Giant covalent structures


  • Made up of a large number of atoms covalently bonded in a network
  • Have high melting and boiling points because lots of energy is needed to break covalent bonds
  • Have a strong, rigid structure
  • Have no free electrons or ions
• Giant covalent structures


  • Diamond
  • Graphite
• Graphite


  • Layers held by weak forces
  • Good lubricant
  • Conducts electricity
• Thermochromic


  Changes colour depending on temperature
• Photochromic 


  Changes colour depending on light
• Hydrogels


  Absorb water
• Shape memory alloy


  Go back to original shape when heated
• Covalent bonding 


  Between non-metals (+hydrogen)
• Nanoparticles


  Very very small
• Titanium dioxide

  • Used in self cleaning windows
  • UV protection
• Nanosilver

  • Antimicrobial
  • On trolly handles to disinfect
• Issues of nanoparticles

  • Long-term effects are unknown
  • Could enter bloodstream
• What are the main properties of metals


  Ductile and malleable
• How does an ionic bond form?


  When a metal and non-metal react together
• How does a covalent bond form?

  Between non-metal atoms
• What are the properties of simple covalent compounds?

  Low melting and low boiling points because of weak intermolecular bonds. They do not conduct electricity
• How can graphite conduct electricity?

  Because of delocalised electrons
• How many covalent bonds in diamond?

  Four
• How many covalent bonds in graphite?

  Three
• Melting point increases as you go up the periodic table