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Chemical properties of Group 7

Chemical properties of Group 7

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Tutor: Alexander

Summary

Chemical properties of Group 7

In a nutshell 

Halogens are reactive non-metals which are found in Group 777​. 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 (20°C)(20 \degree C)(20°C)​​

Colour

Electronic structure

Fluorine
​F2F_2F2​​​
Gas
Pale yellow
1s22s22p51s^22s^22p^51s22s22p5​​
Chlorine
Cl2Cl_2Cl2​​​
Gas
Green
1s22s22p63s23p51s^22s^22p^63s^23p^51s22s22p63s23p5​​
Bromine
Br2Br_2Br2​​​
Liquid
Brown-red
1s22s22p63s23p63d104s24p51s^22s^22p^63s^23p^63d^{10}4s^24p^51s22s22p63s23p63d104s24p5​​
Iodine
I2I_2I2​​​
Solid
Grey-black
​1s22s22p63s23p63d104s24p64d105s25p51s^22s^22p^63s^23p^63d^{10}4s^24p^64d^{10}5s^25p^51s22s22p63s23p63d104s24p64d105s25p5​​


Chemistry; Inorganic chemistry and the periodic table; KS5 Year 12; Chemical properties of Group 7



Boiling points of halogens 

The Group 777​ 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 1−1-1−​ 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

 Cl2(aq) + 2KBr(aq) → 2KCl(aq) + Br2(aq)Cl_2(aq)\ +\ 2KBr(aq)\ \rightarrow\ 2KCl(aq)\ +\ Br_2(aq)Cl2​(aq) + 2KBr(aq) → 2KCl(aq) + Br2​(aq)​​

​Cl2(aq) + 2Br−(aq) → 2Cl−(aq) + Br2(aq)Cl_2(aq)\ +\ 2Br^-(aq)\ \rightarrow\ 2Cl^-(aq)\ +\ Br_2(aq)Cl2​(aq) + 2Br−(aq) → 2Cl−(aq) + Br2​(aq)​​​​



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. 


Chemistry; Inorganic chemistry and the periodic table; KS5 Year 12; Chemical properties of Group 7




Halogen

Colour

Aqueous

Organic

Chlorine
Colourless
Colourless
Bromine
Yellow
Orange
Iodine
Orange/brown
Purple


Halogen

Displacement reaction

Ionic equation 

​ClClCl​​
Chlorine (Cl2)(Cl_2)(Cl2​) will displace Br−Br^-Br− and I−I^-I−​​
​Cl2(aq) + 2Br−(aq) → 2Cl−(aq) + Br2(aq)Cl_2(aq)\ +\ 2Br^-(aq)\ \rightarrow\ 2Cl^-(aq)\ +\ Br_2(aq)Cl2​(aq) + 2Br−(aq) → 2Cl−(aq) + Br2​(aq)
Cl2(aq) + 2I−(aq) → 2Cl−(aq) + I2(aq)Cl_2(aq)\ +\ 2I^-(aq)\ \rightarrow\ 2Cl^-(aq)\ +\ I_2(aq)Cl2​(aq) + 2I−(aq) → 2Cl−(aq) + I2​(aq)​​​
​BrBrBr​​
Bromine (Br2)(Br_2)(Br2​) will displace I−I^-I−​​
​Br2(aq) + 2I−(aq) → 2Br−(aq) + I2(aq)Br_2(aq)\ +\ 2I^-(aq)\ \rightarrow\ 2Br^-(aq)\ +\ I_2(aq)Br2​(aq) + 2I−(aq) → 2Br−(aq) + I2​(aq)​​
​III​​
No reaction with F−,Cl−,Br−F^-, Cl^-, Br^-F−,Cl−,Br−​​



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 (AgNO3)(AgNO_3)(AgNO3​). A precipitate of the silver halide is formed. 


Ag+(aq) + X−(aq) → AgX(s)Ag^+(aq)\ +\ X^-(aq)\ \rightarrow\ AgX(s)Ag+(aq) + X−(aq) → AgX(s) : where XXX​ is ClClCl​, BrBrBr​ or III​.


The colour of the precipitate identifies the halide.


Halide

Precipitate colour

Chloride (Cl−)(Cl^-)(Cl−)​​
White precipitate
Bromide (Br−)(Br^-)(Br−)​​
Cream precipitate
Iodide (I−)(I^-)(I−)​​
Yellow precipitate


Ammonia (NH3)(NH_3)(NH3​) 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 (Cl−)(Cl^-)(Cl−)​​
Dissolves in dilute NH3 (aq)NH_3\ (aq)NH3​ (aq)​​
Bromide ions (Br−)(Br^-)(Br−)​​
Dissolves in conc. NH3 (aq)NH_3\ (aq)NH3​ (aq)​​
Iodide ions (I−)(I^-)(I−)​​
Insoluble in conc. NH3 (aq)NH_3\ (aq)NH3​ (aq)​​
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Predicting reactivity using the periodic table

Unit 1

Predicting reactivity using the periodic table

Displacement reactions

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Displacement reactions

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Chemical properties of Group 7

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Chemical properties of Group 7

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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.

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