T4

• Group 2 metals


  When they react, they lose two electrons to form 2+ ions. This allows them to achieve a full outer shell.
• Group 2 metals


  • Atomic radius increases down the group due to additional electron shells
  • Reactivity increases down the group due to increased electron shielding and increased atomic radius
  • First ionisation energy decreases down the group due to greater atomic radius and increased shielding
• Reactions of Group 2 metals with water

  1. Metal reacts to produce metal hydroxide and hydrogen

  2. Metal hydroxide forms alkaline solution

  
• Reactions of Group 2 metals with water

  • Magnesium reacts slowly with liquid water, but reacts faster with steam to form hydrogen and magnesium oxide

  
• Reactions of Group 2 metals with chlorine

  1. Form metal chlorides which are white precipitates

  2. Reactions become more vigorous down the group
• Reactions of Group 2 metals with oxygen


  1. Form metal oxides

  2. Strontium and barium can form metal peroxides

  
• Reactions of Group 2 metals with dilute acids

  Produce bubbles of hydrogen gas and solutions of metal compounds

  
• Reactions of Group 2 hydroxides with dilute acid

  1. Form a salt and water (neutralisation reaction)

  2. Chloride salts formed with hydrochloric acid

  3. Sulfate salts formed with sulfuric acid

  4. Nitrate salts formed with nitric acid

  
• Solubility of Group 2 hydroxides

  • Solubility increases down the group
  • Magnesium hydroxide is least soluble, barium hydroxide most soluble

  
• Solubility of Group 2 sulfates

  • Solubility decreases down the group
  • Barium sulfate is insoluble and used in medicine as a tracer

  
• Thermal decomposition of Group 2 carbonates

  Produce metal oxide and carbon dioxide
• Thermal decomposition of Group 2 nitrates

  Produce metal oxide, nitrogen dioxide and oxygen

  
• As you go down Group 2, more heat is required for thermal decomposition reactions as the ions increase in size and the carbonates/nitrates increase in thermal stability
• Thermal decomposition of Group 1 carbonates and nitrates

  Lithium acts like Group 2, other Group 1 nitrates produce metal nitrite and oxygen, other Group 1 carbonates won't decompose

  
• Explanation of thermal stability trend

  Smaller ions have higher charge density and can polarise negative carbonate/nitrate ions more, so less heat is required to separate them. Larger cations form more stable carbonates and nitrates.
• Flame tests for Group 1 and 2 elements


  • Each metal has a unique flame colour
  • Colour produced depends on electron transitions and wavelength of light emitted
• Flame test colours for Group 1 elements

  • Lithium - red
  • Sodium - orange/yellow
  • Potassium - lilac
• Flame test colours for Group 2 elements

  • Magnesium - no colour
  • Calcium - brick red
  • Strontium - crimson red
  • Barium - pale green
• Halogens (Group 7 elements)


  Highly reactive non-metals that gain an electron to form 1- ions and achieve a full outer shell

  
• Trends in halogen properties

  • Atomic radius increases down the group
  • Electronegativity decreases down the group due to increased atomic radius and electron shielding
  • Melting and boiling points are low due to simple covalent molecular structure
• Wavelength


  The distance between two consecutive peaks or troughs in a wave
• The colour produced depends on the wavelength of the light energy emitted


  When some electrons drop back down to their original orbital, the energy emitted may not have a wavelength in the visible light part of the electromagnetic spectrum, which explains why not all atoms and ions produce a colour in the flame test
• Group 7 elements (Halogens)


  • Highly reactive non-metals
  • In order to achieve a full outer shell, the halogens gain an electron and form a 1- ion
• Atomic radius


  The distance from the centre of the nucleus to the outermost shell of an atom
• Atomic radius of Group 7 elements

  Increases down the group due to additional electron shells
• Electronegativity


  The ability of an atom to attract shared electrons in a covalent bond
• As you go down Group 7

  Atomic radius and electron shielding increases, so electrons in the outer shells are less strongly attracted to the nucleus and are more easily removed, therefore electronegativity decreases
• Melting and boiling point


  The temperature at which a substance changes from a solid to a liquid (melting point) or from a liquid to a gas (boiling point)
• The Group 7 elements are simple covalent molecules, held together with van der waals forces


  The strength of these intermolecular forces increases as the relative atomic mass of the molecule increases, so more energy is required to overcome them, resulting in higher melting and boiling points
• Reactivity of Group 7 elements

  Decreases down the group as it becomes harder to attract an electron due to increased shielding and atomic radius
• Oxidising agent


  A substance that has the ability to oxidise other substances by accepting electrons
• Oxidising power of the halogens


  Decreases down the group as their ability to attract electrons decreases due to shielding and a greater atomic radius
• A halogen will displace any halide beneath it in the Periodic Table


  Cl2 will displace Br- and I- ions, Br2 will displace I- ions and I2 will not displace any halide ions
• Halide ions


  The negative ions of halogens
• Reducing agent


  A substance that has the ability to reduce other substances by donating electrons
• Reducing power of halide ions

  Increases down the group as electrons are easier to lose from larger ions due to shielding and a larger atomic radius
• Redox reactions between Group 7 halides and H2SO4

  1. Fluoride and chloride ions: No further reactions take place

  2. Bromide ions: HBr is observed as misty fumes, then HBr reduces H2SO4 to produce orange fumes of Br2 and choking fumes of SO2

  3. Iodide ions: HI is observed as misty fumes, then HI reduces H2SO4 to produce solid iodine and choking fumes of SO2, which is further reduced to toxic gas H2S

  
• Disproportionation reaction


  A reaction where a single element is both oxidised and reduced
• Chlorine reacting with cold water

  Produces chlorate(I) ions (ClO-) and chloride ions via a disproportionation reaction
• This disproportionation reaction is used in water treatment systems where chlorine is used in small quantities to kill bacteria