Group 7- The Halogens
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Colour of Fluorine Normal Physical State
Pale Yellow Gas
Colour of Chlorine Normal Physical State
Green Gas
Colour of Bromine Normal Physical State
Red-brown Liquid
Colour of Iodine Normal Physical State
Grey Solid
Trend in Boiling Points Explain
Boiling points increase down group 7. Due to increasing strength of the van der Waals forces as the size and relative mass of the molecules increases. Trend is shown in the changes of physical state from fluorine (gas) to iodine (solid)
Trend in Electronegativity Explain
Electronegativity decreases down group 7. Halogens are all highly electronegative elements. But larger atoms attract electrons less than smaller ones. Due to the electrons being further from the nucleus and are shielded by more electrons
Trend in Reactivity Explain
Decrease in reactivity down group 7. Because the atoms are getting larger. The outer shell is also further away from the nucleus, so the electrons are less strongly attracted to it
Oxidising Ability Where can their relative oxidising strengths be seen?
Halogens become less oxidising down the group. In their displacement reactions
Rule of Displacement in Halogens
A halogen will displace a halide from solution if the halide is below it in the periodic table
Making Bleach
Mix chlorine gas with cold, dilute, aqueous sodium hydroxide you get sodium chlorate (I) solution. This is common household bleach
Equation for making bleach Name of reaction Explain
2NaOH + Cl2 –> NaClO + NaCl + H2O. Disproportionation. Oxidation state of chlorine goes up and down, meaning that chlorine is both oxidised and reduced
Three Main Uses of Sodium Chlorate (I) Solution
Used in water treatment Used to bleach paper Used to bleach textiles
Reaction of Chlorine Mixed with Water Name of Reaction
Produces a mixture of chloride ions and chlorate (I) ions. Disproportionation
Equation for Reaction of Chlorine mixed with Water
Cl2 + H2O <==> 2H+ + Cl- + ClO-
Reaction of Chlorine mixed with Water in Sunlight
Chlorine can decompose water to form chloride ions and oxygen
Equation for Reaction of Chlorine mixed with Water in Sunlight
2Cl2 + 2H2O <==> 4H+ + 4Cl- + O2
Uses of Chlorate (I) Ions
Kills bacteria. When adding chlorine (or a compound containing chlorate I ions) to water it can make it safe to drink or swim in
Three Strengths of adding Chlorine to Drinking Water
• It kills disease-causing microorganisms. • Some chlorine persists in the water and prevents reinfection further down the supply. • It prevents the growth of algae, eliminating bad tastes and smells, and removes discolouration caused by organic compounds
Two Limitations of adding Chlorine to Drinking Water
• Chlorine gas is very harmful if it’s breathed in- it irritates the respiratory system. Liquid chlorine on skin or eyes causes severe chemical burns. Accidents involving chlorine could be very serious or fatal. • Water contains a variety of organic compounds that chlorine can react with to form chlorinated hydrocarbons (eg chloromethane) and many of these chlorinated hydrocarbons are carcinogenic. However, increased cancer risk is small compared to the risks from untreated water