Group 7 elements

• Physical properties

  Down group 7 , boiling and melting point increases because their atomic radius increases due to having more shells. This leads to greater Van Der Waais forces between molecules ( so temporary dipoles are easier to induce ) increasing the energy needed to separate the molecules and therefore higher boiling and melting point.
• Physical properties pt 2

  Down group 7, electronegativity decreases because their atomic radius increases so there's more shielding between the positive nucleus and outer electrons so the electrostatic attraction would be weaker so it's got a weaker ability to attract electrons in an covalent bond
• Uses of Chlorine

  • Used in treatment of drinking water and for swimming pools
  • To kill bacteria
• Chlorine reaction with water

  Chlorine reacts with water in a reversible reaction to form Chloric ( | ) acid (HClO) and hydrochloric acid ( HCl )

  
• Reaction with water pt2

  It's classed as a disproportionation reaction as the chlorine starts off in a zero oxidation state but gets reduced and oxidised at the same time.
• Chlorine reaction with water pt3

  In bright sunlight a different reaction occurs as the new products is hydrochloric acid and Oxygen
• An alternative to direct chlorination of swimming pools is to add solid sodium chlorate or calcium chlorate. These both dissolve in water to form Chloric acid in a reversible reaction.

  In alkaline solutions, the equilibrium above moves to the left which means HClO is converted to ClO- ions so swimming pools a kept slightly acidic

  
• Chlorine reaction with alkali

  Chlorine reacts with cold dilute NaOH to form sodium chlorate ( NaClO ). This is an oxidising agent and a component of household bleach. This is also a disproportionation reaction.

  
• Chlorine reaction with other halides

  KCl + Cl2 --> KCl+ Cl2

  So no reaction takes place and colour of solution remains very pale green

  KCl + Br2 --> KCl + Br2 so no reaction takes place and colour of solution remains yellow

  KCl + I2 --> KCl + I2 so no reaction takes place and colour of solution remains brown
• Bromine reaction with other halides

  2KBr + Cl2 --> 2KCl+ Br2

  So a reaction has taken place and Cl has displaced Br and colour change of solution to yellow

  KBr + Br2 --> KBr + Br2 so no reaction takes place and colour of solution remains yellow

  KBr + I2 --> KBr + I2 so no reaction takes place and colour of solution remains brown
• Iodine reaction with other halides

  KI + Cl2 --> KCl+ I2

  So a reaction takes place and Cl has displaced I and colour of solution changes to brown

  KI+ Br2 --> KBr + I2 so a reaction takes place and Br has displaced I and colour of solution changes to brown

  KI + I2 --> KI + I2 so no reaction takes place and colour of solution remains brown
• Down group 7, the oxidising ability decreases so fluorine is the best oxidising agent
• As you go down group 7 the halide ions have increasing reducing ability, so they would be better a reducing agent

  As you go down group 7 the halide ions have increasing reducing ability so they would be better a reducing agent
• Chlorine is used even though it's toxic is because its used in small quantities and it's health benefits out way the risk