Nov 2001/Paper 3/Section B/Q 8
Chlorine, bromine and iodine are placed in this order in Group VII of the Periodic Table.
(a) State four ways in which the physical or chemical properties of chlorine, bromine and iodine are similar
(b)
(i) Describe the trends in physical properties of chlorine, bromine and iodine.
(ii) How is the trend in chemical reactivity of chlorine, bromine and iodine shown by displacement reactions? Give an equation for a reaction in which one element displaces another from one of its compounds.
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Answer:
(a) More than four are listed below:
- Each molecules contains two atoms. They are diatomic.
- The boiling points of the elements are very low. All of them boil below 200 degrees Celsius.
- The halogens react vigorously with metals to form halide salts.
- They are oxidising agents.
- They are coloured (Chlorine Greenish Yellow, Bromine Brownish, Iodine Purple.)
- They are Non metals.
(b)
(i) Down the group, The boiling points and melting points of the elements increases. At room temperature, chlorine is a gas, bromine a liquid and iodine is a solid. The elements also becomes darker in color down the group.
INFO:
The boiling points increases due to an increased in the mass of the elements. Down the group, as the size of the electron clouds increases with an increase in the number of protons in the nucleus, the forces of attraction is stronger.
It is also noted here that the force of attraction decreases with an increases in electron cloud radius but this effect is negligible as compared with the increased in charge.
(ii) Chlorine > Bromine > Iodine.
2KI(aq) + Cl2(ag)---> 2KCl(aq) + I2 (aq)
INFO:
The reactivity decreasess down the group due to the fact that the outer circle of electrons are further and further away from the nucleus and hence a smaller force of attraction exist to attract an electron from another element.
In this reaction, the aqueous potassium iodide turns brown due to the iodine produced. This is a redox reaction with chlorine being reduced (oxidising agent) and iodine being oxidised(reducing agent)
