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Introduction to Halogens

Chemistry: AQA A Level, topic 3.3.1

Introduction to Halogens

Halogens are found in Group 7 of the periodic table.

Halogens

Halogens

  • Halogens are located in Group 7 of the periodic table.
  • They are non-metals.
  • They tend to form negative ions called halide ions.
  • The halogens are made up of fluorine, chlorine, bromine, iodine and astatine.
Halogen phases

Halogen phases

  • Fluorine - gas.
  • Chlorine - gas.
  • Bromine - liquid.
  • Iodine - solid.
Halogen electron configuration

Halogen electron configuration

  • Fluorine - 1s22s22p5
  • Chlorine - 1s22s22p63s23p5
  • Bromine - 1s22s22p63s23p63d104s24p5
  • Iodine - 1s22s22p63s23p63d104s24p64d105s25p5
Halogen formulae

Halogen formulae

  • Halogens all tend to exist as diatomic molecules.
  • Fluorine - F2
  • Chlorine - Cl2
  • Bromine - Br2
  • Iodine - I2

Properties of Group 7 Halogens

In this section, we will explore some core trends in the properties of the halogens. We will cover electronegativity, boiling point, and solubility of silver halides.

Halogen electronegativity

Halogen electronegativity

  • Electronegativity is how strongly an element attracts a bonding pair of electrons.
  • You should already know that fluorine is the most electronegative element.
  • Electronegativity decreases as you go down Group 7.
  • This is because atomic radius increases and so electrons experience less attraction to the nucleus.
  • Electrons become further away from the nucleus and so experience a lower attraction.
  • This means that the electronegativity is lower.
Halogen boiling points

Halogen boiling points

  • Boiling points increase down the group. At room temperature:
  • Fluorine and chlorine are gases.
  • Bromine is a liquid.
  • Iodine is a solid.
  • This is because elements have more electrons as you go down Group 7.
  • This causes an increase in van der Waals forces.
  • Stronger van der Waals forces means greater intermolecular forces.
  • This means a higher boiling point.
Silver halide solubility in NH3(l)

Silver halide solubility in NH3(l)

  • All silver halides precipitate out of aqueous solution.
  • When ammonia is added, they may dissolve again.
  • Solubility in ammonia decreases as you go down Group 7.

Test yourself on Introduction to Halogens

  • Halogens are found in which Group of the periodic table?

  • Which of the halogens is a liquid at room temperature?

  • Which of the following is true of chlorine?

  • What is the trend of the boiling points of the halogens as you go down the group?

  • Which silver halide (AgX(s)) is least soluble in ammonia?

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