• Chlorides of Period 3 elements show characteristic behaviour when added to water which can be explained by looking at their?chemical bonding?and?structure

Chemical bonding & structure of Period 3 chlorides table

Sodium & magnesium chloride

• NaCl and MgCl₂?do not react with water as the?polar?water molecules are attracted to the ions?dissolving?the chlorides and breaking down the?giant ionic structures: the metal and chloride ions become hydrated ions

The diagram shows water molecules breaking down the giant ionic structure of NaCl and MgCl2?to form hydrated ions

Aluminium chloride

• Aluminium chloride exists in two forms:
  • AlCl₃?as a?giant lattice?and with?ionic?bonds
  • Al₂Cl₆?as a?dimer?with?covalent?bonds

The two forms in which aluminium chloride exists

• When water is added to aluminium chloride the dimers are broken down and Al³⁺?and Cl-?ions enter the solution
• The highly charged Al³⁺?ion becomes hydrated and causes a water molecule that is bonded to the Al³⁺?to lose an H⁺?ion which turns the solution?acidic
• The H+?and the Cl-?form?hydrogen chloride gas?which is given off as?white fumes

The hydrated aluminium causes a water molecule to lose a H⁺?ion turning the solution acidic

Silicon chloride

• SiCl₄?is?hydrolysed?in water, releasing?white fumes of hydrogen chloride gas?in a?rapid?reaction

SiCl₄(l) + 2H₂O(l) → SiO₂(s) + 4HCl(g)

• The SiO₂?is seen as a?white precipitate?and some of the?hydrogen chloride gas?produced dissolves in water to form an?acidic?solution

Phosphorus(V) chloride

• PCl₅?also gets?hydrolysed?in water

PCl₅(s) + 4H₂O(l) → H₃PO₄(aq) + 5HCl(g)

• Both H₃PO₄?and dissolved HCl are highly?acidic