chemistry

• Metallic bonding


  When metal atoms bond together
• Metals


  • Have giant structures of regularly arranged atoms
  • The electrons from the outer shells of the atoms are delocalised – meaning they are free to move through the whole structure
• Metallic bonds


  Formed by sharing delocalised electrons
• Strength of metallic bond


  Due to the force of attraction between the metal ions (+) and the delocalised electrons (-)
• Metallic properties


  • Conduct electricity
  • Conduct heat
  • Malleable and ductile
  • High melting and boiling points
• The melting and boiling points increase as you move across any period of the Periodic table, because there are more delocalised electrons increasing the attraction between the ions and the free electrons (stronger bonds)
• Ion


  A charged particle. Has different numbers of protons and electrons
• Positive ion


  Has more protons (+) than electrons (-)
• Negative ion


  Has more electrons (-) than protons (+)
• Ionic bonding


  The bonding between metal and non-metal atoms
• Ionic bond formation


  Electrons transfer from a metal to a non-metal atom so that both atoms achieve full outer shells
• Covalent bonding


  The bonding between non-metal atoms
• Covalent bond formation

  Atoms share electrons so that both atoms achieve full outer shells
• Covalent bonding


  • Single bonds - 1 pair of electrons shared
  • Double bonds - 2 pairs of electrons shared
• Giant ionic structures


  • Oppositely charged ions attract each other in a regular pattern
  • High melting and boiling points - due to the strength of the electrostatic forces between the ions
  • Conduct electricity when dissolved or molten - only then are the ions free to move to carry the charge
• Simple molecular structures


  • Consist of a few atoms held together by covalent bonds
  • Low melting and boiling points - due to the weak intermolecular forces between the molecules
  • Do not conduct electricity - no free electrons to carry the electric current
• Giant covalent structures


  • Consist of lots of atoms held together by covalent bonds
  • Arranged into giant lattices, which are extremely strong because of the large number of bonds in the structure
• Giant covalent structures


  • Diamond - each carbon bonded to 4 others
  • Graphite - each carbon bonded to 3 others
• Nano-silver


  Used in wound dressings, socks, fridges, deodorants, water disinfection - has properties that bulk silver does not have
• Nano-scale titanium dioxide particles


  Used in sunscreen to block UV light, and in self-cleaning windows
• The use of nano-scale particles is relatively new, so it is not certain what the long term effect of using them will be on our health or the environment
• Smart materials


  Materials that have properties which change reversibly, ie can change easily but can then easily change back, depending on changes in their surroundings
• Indicators


  Substances that change colour when they are added to acids and alkalis
• Litmus


  Turns red in acid and blue in alkalis
• Universal indicator


  Changes colour to show the pH of a solution
• Acidic


  pH < 7
• Neutral


  pH 7
• Alkaline


  pH > 7
• Acids


  Produce hydrogen ions, H+, when they dissolve in water
• Bases


  Chemically opposite to an acid. A base that dissolves in water is called an alkali
• Alkalis


  Produce hydroxide ions, OH-, when they dissolve in water
• Neutralisation reaction


  Happens when an acid and an alkali 'cancel each other out'. The reaction always produces a salt and water
• The H+ ions from the acid react with the OH- ions from the alkali to form water
• Acids reacting with metals


  Produce a salt and hydrogen gas
• The more reactive the metal, the faster the reaction is, resulting in more bubbling and a bigger temperature rise
• Acids reacting with alkalis and bases


  Produce a salt and water
• Acids reacting with alkalis and bases


  • Nitric acid + sodium hydroxide → sodium nitrate + water
  • Sulfuric acid + zinc oxide → zinc sulfate + water
• Acids reacting with carbonates


  Produce a salt, water and carbon dioxide gas
• Acids reacting with carbonates

  • Nitric acid + sodium carbonate → sodium nitrate + water + carbon dioxide
• Ores


  Minerals found in the Earth's crust that contain metal compounds, from which metals can be extracted