The Periodic Table - Groups 0, 1 and 7

Groups in the Periodic Table

1. Group 1: Alkali Metals

   • Properties:
     • React with oxygen to form oxides
       • \[4Li + 0_2 -> 2li_20\]
       • Shiny when freshly cut but tarnish rapidly in moist air
     • React with water to form hydroxides and hydrogen gas
       • Alkali metal + water -> Metal hydroxide + Hydrogen gas
         •  \[2Li + 2 H_2O -> 2LiOH + H_2\]
     • React with chlorine and bromine to form chlorides and bromides
       • \[2Li+Cl_2->2LiCl\]
       • colourless, crystal salts
     • Become more reactive as the group is descended
       • Why?
         • Octet rule: When placing electrons in orbits, the electron configuration with a full outer shell is preferable
           • In a reaction with a non-metal, an alkali metal loses the single electrons in its outermost shell
             • Moving down the group, the atom gets bigger and electrons feel less attraction from the nucleus
               • Giving away the outermost electron becomes easier and hence the elements become more reactive
     • Low melting point
     • Soft
     • Easily cut
   • Can be identified using flame tests
     • Lithium
       • Crimson red
     • Sodium
       • Orange
     • Potassium
       • Lilac

2. Group 7: Halogens

   • Properties
     • All exist as diatomic molecules
     • Density, boiling point and melting point increase moving down the group
     • React with metals to form salts
       •  \[Cl_2 +Mg -> MgCl_2\] \[F_2 + 2Na -> 2NaF\]
       • These salts have many uses
         • NaCl - Table salt
         • NaBr - Disinfectant for pools
     • Can be used as disinfectants and bleaches as they kill microorganisms and remove colour
     • React with hydrogen to form hydrogen halides
       • \[H_2 + Cl_2 -> 2HCl\]
       • When these halides dissolve in water, they break up into a positive and negative ion
     • Reactivity decreases down the group
       • A more reactive halogenw ill displace a less reactive halogen in a displacement reaction
       • According to the octet rule, halogens gain one electron when they react
         • Moving down the group, atoms become bigger and electrons feel less attraction from the nucleus
           • Gaining an electron becomes less favourable and hence elements become less reactive
   • Can be identified using a precipitation reaction with silver nitrate
     • \[Ag^{+}(aq)+Cl^{-}(aq)-> AgCl(s)\]
     • Chloride
       • White
     • Bromide
       • Pale yellow
     • Iodide
       • Yellow

3. Group 0: Noble gases

   • Properties
     • Colourless
     • Low melting and boiling points points
     • Poor conductors of heat and electricity
     • Inert: They do not react easily
       • Octet rule is already satisfied since they have a full outer shell
     • Exist as single atoms
   • Uses
     • Helium : Weather balloons
       • Low density and non-flammable
     • Neon: long lasting illuminated signs
       • Produces a distinctive red-orange light when electricity is passed through it