4.2 - Group 1, Alkali Metals

• trends in atomic radii

  increases down the group due to more shells

  more shells means more inner elections so will take up more space as elections repel each other so atoms get bigger
• trend in first ionisation energies

  decreases down the group due to more shells so increases distance between outer election and nucleus and shielding so it's less strongly attracted to nucleus so easier to remove
• trend in electronegativity


  decreases down the group as atoms get bigger so bonding elections get further from the nucleus so are less attracted to it so it's harder to attract bonding electrons
• trends in melting and boiling points

  decreases down the group because atoms get bigger so nuclei gets further away from delocalised electrons so are less attracted to each other so less energy needed to overcome electrostatic forces of attraction
• trends in density


  increases down the group
• physical properties


  soft - easily cut with a knife

  shiny when freshly cut but become dull when they react with Moisture or oxygen (so are wept in oil to protect from air)
• Oxidation state


  +1
• uses of lithium


  lithium carbonate is used in drugs to treat mental illness

  other compounds are important reagents for organic synthesis
• uses of sodium


  powerful reducing agent used to extract titanium & other metals

  sodium vapour used in street lights

  commercial uses - sodium hydroxide is the most important industrial Alkali
• uses of potassium


  ions are essential nutrient in plants

  ingredient in NPK fertilisers
• reaction with water general equation

  2X + H2O → 2XOH + H2
• reaction of lithium with water

  floats on surface and gently fizzes giving off hydrogen

  gradually disappears forming colourless lithium hydroxide
• reaction of sodium with water


  floats on surface & melts forming a small silvery ball that dashes around the surface

  white trail of sodium hydroxide is seen but dissolves into colourless sodium hydroxide
• reaction of potassium with water

  floats then melts & sets light to hydrogen which produces a lilac flame
• reaction of rubidium with water


  sinks & reacts immediately with everything spitting out of the container
• reaction of caesium with water

  explodes on contact with water shattering container
• trend in reactivity with water

  becomes more reactive down the group because energy to form positive ions falls due to decrease in first ionisation energy & fall in atomisation energy so metals have a weaker metallic bond which leads to lower activation energies so faster reactions
• why are different oxides formed when group 1 metals react with air or Oxygen

  depends how far down the group you are

  forming more complicated oxides releases more energy & makes system more energetically stable but it only works with metals down the group because they have a lan charge density and are big
• trend in reactivity with air or oxygen


  reactivity increases down the group
• storing group 1 metals

  must be stored out of contact with air to prevent Oxidation as they are very reactive
• storage of lithium, sodium and potassium

  stored in oil as they're less reactive than other metals in the group
• storage of rubidium o caesium

  stored in sealed gas tubes in a vaccuum or in an inert atmosphere (using noble gas)
• reaction of lithium with air

  burns with a strongly red-tinged flame

  reacts with oxygen in air to give white lithium oxide
• reaction of lithium with pure oxygen

  red-tinged flame would be more intense

  produces lithium oxide
• reaction of lithium with nitrogen in air

  gives lithium nitride

  Li3N
• reaction of sodium in air

  small pieces give an orange glow

  larger pieces give a strong range flame producing white solid mixture of sodium oxide or sodium peroxide
• reaction of potassium in air

  large pieces burn with a lilac flame

  small pieces melt & turn into a Mixture of potassium peroxide & potassium superoxide
• reaction of rubidium & caesium in air

  both catch fire and produce superoxides
• reaction of simple oxides with water

  X2O + H2O → 2XOH
• reaction of simple oxides with dilute acids

  X2O + 2HCI → 2XCI + H2O
• reaction of peroxides with water

  X2O2+ 2H2O → 2XOH + H2O2

  at higher temperatures hydrogen peroxide decomposes into water and hydrogen
• reaction of peroxides with dilute acids

  X2O2+2HCI → 2XCI+ H2O2
• reaction of superoxides with water

  2XO2+ 2H2O → 2XOH+ +H2O2+O2

  heat produced will decompose hydrogen peroxyde into water and Oxygen
• reactions of superoxides with dilute acids

  2XO2 + 2HCI→2XCI + H2O2 + O2

  hydrogen peroxide decomposes into water & oxygen
• reaction with chlorine

  2X + CI2 → 2KCI

  produces colourless ionic chlorides soluble in water

  solid white residue of