4.1.2 group 7

• Halogens are in group 7
• Halogens have 7 electrons in their outer shell
• When halogens react, they gain 1 electron to get a full outer shell. By gaining 1 electron, they form a negative ion
• Halogens share electrons to make diatomic molecules
• When a metal atom transfers its outer electron to a non-metal atom, like a group 7 atom, salts are formed. The result is a compound where all the ions have a full outer shell.
• As you go down group 7, the halogens become less reactive. This is because:

  • the atoms gain more electron shells
  • the outer electron shell is further from the nucleus
  • the attraction between the nucleus and the electron (to be gained from another element) decreases
• Properties of halogens:

  • 7 outer electrons
  • form salts
  • get less reactive down group
  • diatomic molecules
• Bromine (Br2) - at room temperature:

  • red-brown colour
  • liquid state
• Chlorine (Cl2) - at room temperature:

  • pale green colour
  • gaseous state
• Iodine (I2) - at room temperature:

  • dark grey colour
  • solid state
• Halogen states at room temperature:

  A) pale green

  B) chlorine

  C) dark grey

  D) solid

  E) red-brown

  F) bromine