Chemical properties of Group 7
Select Lesson
Exam Board
Select an option
Practical skills
Amino acids, proteins and DNA
Aromatic chemistry, amines and polymers
Isomerism and carbonyls
Transition metals
Acids and bases
Electrode potentials and cells
Rate equations
Thermodynamics
Alkenes and alcohols
Alkanes and halogenoalkanes
Organic chemistry - the basics
Group 2 and 7 elements
Kinetics, equilibria and redox
Energetics
Bonding
Amount of substance
Explainer Video
Summary
Chemical properties of Group 7
In a nutshell
Halogens are reactive non-metals which are found in Group . Their boiling points increase as you go down the group whilst their reactivity decreases as you go down the group. A more reactive halide will displace a less reactive halide. Halides can be tested for with silver nitrate.
The halogens
Halogen | Formula | State at | Colour | Electronic structure |
| Fluorine | | Gas | Pale yellow | |
| Chlorine | | Gas | Green | |
| Bromine | | Liquid | Brown-red | |
| Iodine | | Solid | Grey-black | |
Boiling points of halogens
The Group elements are simple covalent molecules which are held together by weak van der Waals forces. The strength of these forces increases as the atomic radius increases, this means that more energy would be required to overcome these forces. As you go down the group this would lead to an increase in boiling point.
Halogens reactivity
Halogens are generally highly reactive non-metals and gain an electron to form a ion, to achieve a full outer shell. As the atomic radius increases down the group, it is more difficult to attract an electron as the shielding effect increases thus weakening the attraction between the nucleus and outer electrons. Halogen ions are reduced as they gain an electron, they oxidise another substance, making them oxidising agents.
Displacement reactions
Halogens displace less reactive halides. Halogens' relative oxidation strengths can be seen in their displacement reactions with halide ions. The relative oxidising strengths of halogens mean a halogen will displace any halide beneath it in the periodic table.
Example
Displacement reactions to identify halides
Displacement reactions can be used to help identify which halogen is present in a solution. When a displacement reaction occurs, there are colour changes. These colour changes can be easily seen when shaking and mixing with hexane. A clear distinct layer will form. The halogen which is displaced will dissolve into the hexane layer whilst the more reactive halogen will remain in the aqueous layer.
Halogen | Colour | |
Aqueous | Organic | |
| Chlorine | Colourless | Colourless |
| Bromine | Yellow | Orange |
| Iodine | Orange/brown | Purple |
Halogen | Displacement reaction | Ionic equation |
| | Chlorine will displace and | |
| | Bromine will displace | |
| | No reaction with | |
Testing for halides
To test for halides using silver nitrate, add dilute nitric acid to remove ions which may interfere with the test. Next, add silver nitrate solution . A precipitate of the silver halide is formed.
: where is , or .
The colour of the precipitate identifies the halide.
Halide | Precipitate colour |
| Chloride | White precipitate |
| Bromide | Cream precipitate |
| Iodide | Yellow precipitate |
Ammonia can be further used to indicate the halide ions present with different concentrations of ammonia giving different results. The greater the atomic radius of a halide, the more difficult it is to dissolve.
Halide | Solubility |
| Chloride ions | Dissolves in dilute |
| Bromide ions | Dissolves in conc. |
| Iodide ions | Insoluble in conc. |
FAQs - Frequently Asked Questions
What is the main force involved in halogens?
The main forces which is involved in halogens is van der Waals, which is a weak electrostatic attractive force.
How does the reactivity of halogens change as you go down the group?
The halogens get less reactive as you go down the group. This is due to a larger atomic radius, which makes it more difficult for the halogen to attract an electron to fill its outer shell.
Where can the halogens be found in the periodic table?
The halogens can be found in Group 7 of the periodic table.