Group: VII: Halogens, Halides and Chlorine

Edited by Jamie (ScienceAid Editor), Taylor (ScienceAid Editor), Administrator

the halogens

Ad

Properties of Halogens

  1. 1
    Electronegativity.
    The electronegativity of halogens decrease down the group. Fluorine is very reactive and is the most electronegative element.
    Advertisement
    Was this step helpful? Yes | No | I need help

  2. 2
    Boiling Point.
    A further physical property is the halogen's boiling point, which increase down Group 7. This is because the atoms get bigger and so the Van der Waals forces get larger as well.
    Was this step helpful? Yes | No | I need help

  3. 3
    Oxidization.
    And now a chemical property. The oxidizing power of the halogens decreases from Fluorine to Iodine. This property can be demonstrated by displacement reactions.This means if halogen ions are dissolved in water. If a halogen higher up the group is added; this higher halogen will replace it. For example, when chlorine is added to Br-(aq), the following reaction takes place.
    Was this step helpful? Yes | No | I need help

    Advertisement

2Br-(aq) + Cl2 ® 2Cl-(aq) + Br2

Halides

A halide is simply the ion of a halogen. Their ability to reduce increases down the group from F to I. This ability is shown in the reactions of NaX (where X is a halogen) with sulphuric acid, or as chemists like to call it: H2SO4. The table below shows the results of the reactions of NaX with sulphuric acid.

Was this helpful? Yes | No | I need help

NaX Observations Products
Fluorine Steamy fumes HF
Chlorine Steamy fumes HCl
Bromine Steamy fume

Colourless gas Brown fumes

HBr

SO2 Br2

Iodine Steamy fumes

Colourless gas Yellow solid Rotten eggs smell A black solid a purple fumes

HI

SO2 S H2S I2

What this demonstrates is that more products are formed with the sodium halides further down the group, therefore reducing the ability of these halides is greater at the bottom of the group.

How to Test for Halides

Now - how to test for the presence of the different halides. A classic test is to add silver nitrate, and it produces a precipitate of different colours depending on the halide. However, as you can see below, the difference in colours is not very distinct. Therefore we add another substance: ammonia. First, a few drops of dilute ammonia are added to the precipitate to see how much it dissolves. Chlorine will dissolve quite well. Bromine will dissolve sparingly and Iodine not at all. Then we add concentrated ammonia and the precipitate in both the chloride and bromide solutions will dissolve and the iodided precipitate turns white. The diagram below outlines this testing procedure.

Was this helpful? Yes | No | I need help

testing halides

The ionic equation for this reaction is as follows (using Br as the halide).

Cl-(aq) + Ag+(aq) ® AgCl(s)

Salt Formation

Halogens will react with metals to form salts. For example, if chlorine gas is passed over a heated iron wire, you will see a brown solid upon cooling.

iron + chlorine ® iron (III) chloride 2Fe(s) + 3Cl2 (g) ® 2FeCl2 (s)

The most reactive halogen is fluorine, and they become less reactive as you go down. Due to this, a more reactive halogen will displace a less reactive one. For example, when chlorine gas is bubbled though potassium bromide solution...

Was this helpful? Yes | No | I need help

2KBr(aq) + Cl2 (g) ® 2KCl (aq) + Br2 (aq)

Chlorine and Chlorides

Chlorine has a very interesting reaction with water. It's a reversible reaction and also shows something called disproportionation [dis-pro-por-shon-ay-shon].

reaction of chlorine and water

Disproportionation defines a reaction where one species (in this case chlorine) is simultaneously oxidized and reduced. If you have a look at chlorine in HCl, it has an [chemistry/physical/redox.html|oxidation number] of -1 and in hydrogen chlorate. This reaction has been used in water treatment to destroy bacteria, however this practice has been replaced by granular calcium hypochlorite Ca(ClO)2 which is less dangerous.

Was this helpful? Yes | No | I need help

Another reaction we are going to look at is chlorine with cold, dilute sodium hydroxide (NaOH). This causes the following reaction to take place.

Cl2 + 2OH- ® Cl- + ClO- + H2O

This reaction is very important because it is used commercially to produce bleach!

Comments

ScienceAid welcomes all comments. If you do not want to be anonymous, register or log in. It is free.




Jamie
Featured Author
166 Articles Started
1,267 Article Edits
42,900 Points
Jamie is a featured author with ScienceAid. Jamie has achieved the level of "Captain" with 42,900 points. Jamie has started 166 articles (including this one) and has also made 1,267 article edits. 8,700 people have read Jamie's article contributions.
Jamie's Message Board
Jamie: Hi, my name is Jamie.
Jamie: Can I help you with your problem about "Group: VII: Halogens, Halides and Chlorine"?
 

Article Info

Categories : Inorganic

Recent edits by: Taylor (ScienceAid Editor), Jamie (ScienceAid Editor)

Share this Article:

Thanks to all authors for creating a page that has been read 29 times.

Do you have a question not answered in this article?
Click here to ask one of the writers of this article
x

Thank Our Volunteer Authors.

Would you like to give back to the community by fixing a spelling mistake? Yes | No