The halogens group 7

• • The elements in Group 7 are known as the halogens
  • These are fluorine, chlorine, bromine, iodine and astatine
  • These elements are non-metals that are poisonous
• • The elements in Group 7 are known as the halogens
  • These are fluorine, chlorine, bromine, iodine and astatine
  • These elements are non-metals that are poisonous
• • Halogens are diatomic, meaning they form molecules made of pairs of atoms sharing electrons (forming a single covalent bond between the two halogen atoms) such as F2, Cl2, etc
• • When halogen atoms gain an electron during reactions, they form -1 ions called halide ions
• • All halogens have similar reactions as they each have seven electrons in their outermost shell
• • At room temperature, the halogens exist in different states and colours, with different characteristics
• Fluorine 


  State and appearance at room temp:

  Yellow gas

  Characteristics:

  Very reactive, poisonous gas
• Chlorine 


  State and appearance at room temp:

  Pale yellow-green gas

  
  

  Characteristics :

  reactive, poisonous and dense gas

  
  

  Colour in solution :

  pale green
• Bromine 


  State and appearance at room temp:

  Red-brown liquid

  
  

  Characteristics:

  dense red - brown volatile liquid

  
  

  Colour in solution:

  Orange
• Iodine

  State and appearance at room temp:

  grey solid

  
  

  Characteristics:

  Shimmery, crystalline solid that sublimes to form a purple Vapor

  
  

  Colour in solution:

  dark brown
• • The melting and boiling points of the halogens increase as you go down the group
  • This is due to increasing intermolecular forces as the atoms become larger, so more energy is required to overcome these forces
• Reactivity of Group 7 non-metals decreases as you go down the group
• However, halogen atoms form negative ions when they gain an electron to obtain a full outer shell
• • This means that the increased distance from the outer shell to the nucleus as you go down a group makes the halogens become less reactiveThe
• Fluorine is the smallest halogen,( smallest atom because of less electron shells), which means its outermost shell is the closest to the positive nucleus of all the halogen

  • Therefore, the ability to attract an electron is strongest in fluorine making it the most reactive
• • As you move down the group, the forces of attractionbetween the nucleus and the outermost shell decreases
  • This makes it harder for the atoms to gain electrons as you descend the group
  • Therefore, the halogens are less reactive the further down the group you go
• • A halogen displacement reaction occurs when a more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide
• Displacement reaction chlorine with bromine or iodine

  • If you add chlorine solution to colourless potassium bromide or potassium iodide solution a displacement reaction occurs:
  • The solution becomes orange as bromine is formed or
  • The solution becomes brown as iodine is formed
• • Chlorine will displace bromine or iodine from an aqueous solution of the metal halide
• • Chlorine will displace bromine or iodine from an aqueous solution of the metal halide

  chlorine + potassium bromide →  potassium chloride + bromine

  Cl2 + 2KBr → 2KCl + Br2

  
  

  chlorine + potassium iodide →  potassium chloride + iodine

  Cl2 + 2KI → 2KCl + I2
• • Bromine will displace iodine from an aqueous solution of the metal iodide

  bromine + potassium iodide →  potassium bromide + iodine

  Br2 + 2KI → 2KBr + I2
• Ionic equation displacement reaction of chlorine and potassium bromide 


  Cl2 + 2Br- → 2Cl- + Br2
• Ionic equation of displacement reaction chlorine and potassium iodide 


  Cl2 + 2I- → 2Cl- + I2
• Ionic equation displacement reaction of bromine and potassium iodide 


  Br2 + 2I- → 2Br- + I2
• Metal halides

  • Chlorine, bromine and iodine react with metals and non-metals to form compounds
• Metal halides

  • The halogens react with some metals to form ionic compoundswhich are metal halide salts
• • The rate of reaction is slower for halogens which are further down the group such as bromine and iodine
• Nonmetal halides

  • The halogens react with non-metals to form simple molecular covalent structures
  • For example, the halogens react with hydrogen to form hydrogen halides (e.g., hydrogen chloride)
• • Reactivity decreases down the group, so iodine reacts less vigorously with hydrogen than chlorine (which requires light or a high temperature to react with hydrogen)
  • Fluorine is the most reactive (reacting with hydrogen at low temperatures in the absence of light)