Inorganic Chemistry: Halogens Chemistry

1. Halogens
Group VIIA

2. Properties in Common
★ six elements
★ all form diatomic molecules (H2, F2, Cl2, Br2, I2, and At2)
★ all form negatively charged ions (H-, F-, Cl-, Br-, I-, and At-
★ Astatine is ignored because it is radioactive
★ salt formers
★ none of the halogens can be found in nature in their elemental
form.
★ found as salts of the halide ions

3. The Halogens in their Elemental Form
Fluorine (F2)
❏ highly toxic, colorless gas, is the most reactive element known
❏ so reactive it even forms compounds with Kr, Xe, and Rn
❏ attacks both glass and quartz
❏ difficult to find a container in which it can be stored
❏ powerful oxidizing agent
❏ handled in equipment built out of certain alloys of copper and
nickel
❏ used in the manufacture of Teflon and freons

4. Chlorine (Cl2)
● highly toxic gas with a pale yellow-green color
● strong oxidizing agent
● used commercially as a bleaching agent and disinfectant
● used to make solvents such as:
1. carbon tetrachloride (CCl4),
2. chloroform (CHCl3),
3. dichloroethylene (C2H2Cl2), and
4. trichloroethylene (C2HCl3)

5. Bromine (Br2)
❏ reddish-orange liquid with an unpleasant, choking odor
❏ Name- Greek stem bromos, "stench."
❏ used to prepare flame retardants, fire-extinguishing agents,
sedatives, antiknock agents for gasoline, and insecticides.

6. Iodine
❏ intensely colored solid with an almost metallic luster
❏ relatively volatile, and it sublimes when heated to form a violet-colored
gas
❏ Used as disinfectant in "tincture of iodine."
❏ compounds are used as catalysts, drugs, and dyes
❏ Silver iodide (AgI) plays an important role in the photographic process
and in attempts to make rain by seeding clouds.
❏ Iodide is also added to salt to protect against goiter, an iodine deficiency
disease characterized by a swelling of the thyroid gland.

7. Common Properties
regular increase in many of the properties of the halogens as we proceed down
the column from fluorine to iodine, including:
❏ the melting point
❏ boiling point
❏ intensity of the color of the halogen
❏ the radius of the corresponding halide ion
❏ the density of the element

8. Common Properties
regular decrease in the first ionization energy as we go down this
column, therefore;
F2 > Cl2 > Br2 > I2
oxidizing strength
And
I- > Br- > Cl- > F-
reducing strength

9. Methods of Preparing the Halogens from their Halides
❏ by reacting a solution of the halide ion with any substance that is a stronger
oxidizing agent
2 I-(aq) + Br2(aq) ----> I2(aq) + 2 Br-(aq)
2 Br-(aq) + Cl2(aq) ----> Br2(aq) + 2 Cl-(aq)
❏ To prepare Cl2, we need a particularly strong oxidizing agent, such as
manganese dioxide (MnO2).
2 Cl-(aq) + MnO2(aq) + 4 H+(aq) ----> Cl2(aq) +
Mn2+(aq)+ 2 H2O(l)

10. ❏ The synthesis of fluorine escaped the efforts of chemists for almost 100
years.
❏ The best way of producing a strong reducing agent is to pass an electric
current through a salt of the metal. Sodium, for example, can be prepared by
the electrolysis of molten sodium chloride.
electrolysis
2 NaCl(l) ----> 2 Na(s) + Cl2(g)
❏ In theory, the same process can be used to generate strong oxidizing agents,
such as F2.