topic 6

• alkali metal

  • found in group one
  • must loss one electron to obtain full outer shell
  • forms +1 ion
  • held together by metallic bonding
  • have low density - can float
  • low melting points - but still solid at room temp
  • alkali are soft metals - can be cut with knife
• alkali metals reaction with water

  • alla alkali metals react with water to form a metal hydroxide and hydrogen gaa
  • eg ; lithium + water > lithium hydroxide + hydrogen
• Observation of alkali metals reacting with water

  • lithium- floats of water , fizzes ( production of hydrogen ) until reaction is complete
  • sodium - reacts strongly with water , has a lower melting point > reaction has enough energy to melt metal , molten ball of sodium whizzes in surface of the water ( releasing hydrogen ) until reaction is complete
  • potassium - reacts even stronger , hydrogen is produced during the reaction , catching fire producing a lilac flame
• Alkali metals have low density, which allows them to float on water.
• Alkali metals are held together by metallic bonding.
• Alkali metals have a low melting point and are still solid at room temperature.
• reactivity of alkali metals

  • reactivity increases going down the group
  • the atom of each element gets larger down the group
  • the outer shell is further away from the nucleus and is shielded by more electron shell
  • further the electron from the positive nucleus , the easier to loss electron in reaction
  • reactivity increase going down the group
• group 7 - halogens

  • have 7 electrons on outer shell
  • must gain an electron to form a full outer shell
  • ion charge is -1
  • they from diatomic molecules
• Halogen appearance - at room temp

  • fluorine - pale yellow gas
  • chlorine - yellow green gas
  • bromine - brown liquid
  • iodine - grey solid
• reactivity of halogens

  • reactivity decrease down the group
  • down the group atoms get larger
  • further away the positive nucleus for outer shell
  • further the outer shell is from positive attraction of the nucleus , harder to attract electron to form full outer shell
• halogen reaction with metals

  • react with metals to form metal halide
  • eg potassium + bromine -> potassium bromide
  • halogen reactivity , allows them to readily react with most metals
  • halogen needs to gain an electron to get full outer shell
  • metals need to lose electron to get full outer shell
  • reacts and from ionic bonding
  • metal halides are formed - type of salt
• halogen reaction with hydrogen

  • halogens react with hydrogen gas to form hydrogen halides
  • chlorine + hydrogen - explodes in bright sunlight but reacts slowly in the dark
  • bromine + hydrogen - reacts slowly on heating with platinum catalyst
  • iodine + hydrogen - combines partially and very slowly with hydrogen , even when heating
• hydrogen halides reacting with water

  • hydrogen halides form acids which they are dissolved in water
  • hydrogen chloride + water > hydrochloric acid
• halogen displacement reaction

  • halogen displacement reactions are redox reactions
  • more reactive halogen displaces less reactive halogen from their compound
  • less reactive halogen cannot displace more reactive from their compound - no reaction occurs
  • more reactive halogen will be reduced as it is gaining electrons
  • less reactive halogen will be oxidised as it is losing electrons
• halogen displacement summery

  • chlorine reacts with potassium bromide and potassium iodide ( both halogen less reactive than chlorine )
  • bromine no reaction with potassium chloride ( chlorine more reactive than bromine ) , reacts with potassium iodide ( iodine less reactive than bromine )
  • iodine has no reaction with potassium chloride or potassium bromide as it is less reactive than both
• Group 0 - the noble gases

  • noble gases already have full outer shells
  • making nobles gases inert - no reaction , very unreactive
• noble gases reactivity

  • do not gain or lose electrons as already has full outer shell
  • noble gases are very stable and mostly unreactive ( inert )
  • all noble gases are similarly unreactive up and down the group
  • they normally do not form bonds with other elements
  • they are monatomic , existing as individual atoms - most other gases are diatomic
• properties of noble gases

  • all noble gases are gases at room temperature > low boiling point
  • gas particles are spread far apart > have low densities
  • as you go down group 0 :
  • boiling points of noble gases increases
  • the density of noble increase
• uses of noble gas

  • xenon and argon - inside filament light bulbs , instead of air to stop hot filament reacting with oxygen and burning away
  • argon and helium - used in welding - they form a blanket over the hot metal - preventing any reaction with oxygen in the air
  • argon - non flammable , using in fire extinguisher systems , denser than air so used to prevent oxygen reacting with wine in barrels
  • helium - has low density - used to fill up balloons and airships
  • electrical current passed through tube filled with neon under lower pressure , coloured light is produced
• uses of noble gases

  1. Xenon and argon in filament light bulbs to prevent filament oxidation.
  2. Argon and helium in welding to shield hot metal from oxygen.
  3. Argon in fire extinguisher systems due to its non-flammability and use for wine preservation.
  4. Helium for inflating balloons and airships.
  5. Neon under low pressure for colorful lights in fluorescent lamps and advertising displays.