Chemical Properties of Halogen Elements and Hydrogen Halides

Group 17 of the periodic table is named Halogens as they all produce sodium salts with similar properties. The chemical properties of halogens [ fluorine (F), chlorine (Cl), bromine (Br), and iodine (I)] are summarized below.

Chemical Properties of Halogen Elements and Hydrogen Halides
Chemical Properties of Halogen Elements and Hydrogen Halides

Oxidizing Properties of Halogen Elements

Halogens are excellent oxidizing agents. The loss of electrons is referred to as oxidation. It takes into account how one halogen can oxidize the ions of another and how this alters the group.

  • By removing an electron from the metal, halogens oxidize it (the oxidation number of the metal increases)
  • Halogens are reduced when they absorb an extra electron from a metal atom (the oxidation number of the halogen decreases)

Halogens react with metals by accepting an electron from the metal atom to form a (-1) charged ion.

X2 + 2e → 2X

The halide ion thus formed will have low bond energy and a high electron affinity. As the nuclear pull on the outer electrons decreases, so do bond energies and electron affinities.

Because of the change in electron affinities, oxidizing ability decreases down the group as the nuclear pull on the outer electrons decreases.

HalogensReactionsDescription
Fluorine2F2+H2O→4HF+O2Fluorine oxidizes water to oxygen, as shown in the equation making it impossible to perform reactions in an aqueous solution.
Chlorine Cl2 + 2Br→ 2Cl+Br2Chlorine can oxidize bromide ions to bromine. Bromine produces an orange solution.
Cl2 + 2I→ 2Cl+ I2Iodide ions can also be converted to iodine by chlorine. If there is not enough chlorine, the iodine appears as a red solution; if there is too much chlorine, it appears as a dark gray precipitate.
BromineBr2+ 2I→ 2Br+ I2Bromine can only oxidize iodide ions and is weakly oxidizing to convert chloride ions to chlorine.
A red iodine solution is formed until the bromine is in excess. The precipitate becomes dark grey.

Comparison of Oxidizing Character of Halogens

  1. Fluorine is such a strong oxidizing agent and oxidizes all halides to halogens.
  2. Chlorine can accept electrons from both bromide ions and iodide ions. Bromine and iodine are unable to reclaim the electrons released by the chloride ions. Hence, chlorine is a more potent oxidizing agent than bromine or iodine.
  3. Bromine is a stronger oxidizer than iodine as it can remove electrons from iodide ions to form iodine.
  4. Except for the extremely radioactive and rare astatide ions, iodine will not oxidize any of the other halide ions.

Reaction of Halogens with Hydrogen

Halogens form hydrogen halides when they react with hydrogen gas.
The reactions between halogen and hydrogen gas become less vigorous as the reactivity of the halogens decreases down the group.

Chemical ReactionsConditionsDescription
H₂ (g) + F₂ (g)→ 2HF (g)In DarkFluorine combines explosively with hydrogen
H₂ (g) + Cl₂ (g) → 2HCl (g)In SunlightReacts with explosive violence
H₂ (g) + Br₂ (g)→ 2HBr (g)HeatWhen bromine vapor and hydrogen are ignited, they produce a mild explosion.
H₂ (g)+ I₂ (g) ⇌ 2HI (g)HeatEven when heated continuously, iodine and hydrogen combine only partially. They form an equilibrium mixture.
Reaction between halogens and hydrogen

Reaction of Halogen with Oxygen

When halogens react with oxygen, many of the resulting compounds are unstable and only last for a few moments.

They have structures ranging from X 2O to X2O7, where X represents a halogen. Their expanded octets enable them to bond with multiple oxygen atoms at once.

Fluorine and oxygen combine to form OF2, also known as oxygen fluoride. It adopts oxidation state (-1).

2F2 + 2NaOH → OF2+ 2NaF + H2O

Halogens other than fluorine forms oxo acids instead of oxides.

ChlorineBromineIodineOxidation States
HOClHOBrHOI+1
HClO2+3
HClO3HBrO3HIO, HIO3+5
HClO4HBrO4HIO4, H5IO6+7

Reaction of Halogens with Phosphorus

In the first instance, all halogens react with phosphorus to form phosphorus(III) halides of the form PX3.

Phosphorus reacts with excess chlorine or bromine to form phosphorus(V) chloride or bromide.

Trihalides (PX3)Pentahalides (PX5)
1. Reaction with white Phosphorus
P4 + 6Br2 → 4PBr3
2. Reaction with red Phosphorus
2P + 3Br2 → 2PBr3

Reaction with white phosphorus
P4 +10Cl2 → 4PCl5

White phosphorus is more reactive than red phosphorus

Reaction of Halogen with Sodium

All the halogens react with sodium to form sodium halides. The common example of the reaction is as follows,

Na + X → NaX

When hot sodium and chlorine gas react, they produce a bright orange flame and white sodium chloride.

Hot sodium will also burn in the presence of bromine or iodine vapor to form sodium bromide or sodium iodide.

Reaction of Halogens with Iron

Iron burns in halogen vapor, forming iron(III) halides except for iodine. On the other hand, Iodine is less reactive and produces iron(II) iodide.

HalogenChemical ReactionDescription
Fluorine2Fe+3F2 → 2FeF3Iron(III) fluoride is formed when cold iron wool burns in cold fluorine. Anhydrous iron(III) fluoride is either white or pale green.
This is a fast reaction in which the iron burns and is oxidized to an iron(III) compound.
Chlorine2Fe+3Cl2 → 2FeCl3When chlorine gas comes into contact with hot iron, it produces iron(III) chloride. Anhydrous iron(III) chloride forms black crystals; any trace of water in the apparatus or chlorine reacts with the crystals, causing them to turn reddish-brown.
Bromine2Fe+3Br2 → 2FeBr3A similar, slightly less vigorous reaction occurs when bromine vapor is passed over hot iron. Anhydrous iron(III) bromide is typically a reddish-brown solid.
IodineFe+2I2 → FeI2The reaction of hot iron with iodine vapor produces gray iron(II) iodide, which is much less vigorous. It is difficult to perform because the product is always contaminated with iodine.

Reaction with other Halogens

When halogens react with other halogens, they form interhalogens.

Interhalogens have the general formula XYn, where n = 1, 3, 5, or 7. In this case, X represents the less electronegative halogen, and Y represents the more electronegative halogen.

There are four general type of interhalogens:

Types Interhalogens
AXClF, BrF, BrCl, ICl, IBr,
AX3ClF3, BrF3, (ICl3)2
AX5ClF5, BrF5, IF5
AX7 IF7
  • The interhalogen compounds of type AX and AX3 are formed between the halogen having very low electronegative differences.
  • The interhalogen compounds of type AX5 and AX7 are formed by larger atoms having low electronegativity with the smaller atoms having high electronegativity. This is because a greater number of smaller atoms can be crammed around a larger one.

Also Read out about chlorine and their reactions https://thechemistrynotes.com/chlorine-element/

References

  1. Smith, D. (1990). Inorganic Substances: A Prelude to the Study of Descriptive Inorganic Chemistry (Cambridge Texts in Chemistry and Biochemistry). Cambridge: Cambridge University Press. doi:10.1017/CBO9780511622922
  2. Lee, J D. Concise Inorganic Chemistry. London: Blackwell Science, 2006. Print.
  3. Cotton, F A, and F A. Cotton. Advanced Inorganic Chemistry. , 1999. Print.
  4. Mingos, D. M. P. Essential Trends in Inorganic Chemistry. Oxford University Press, 1998.
  5. https://www.savemyexams.co.uk/as/chemistry/cie/22/revision-notes/2-inorganic-chemistry/2-3-group-17/2-3-2-chemical-properties-halogens–hydrogen-halides/
  6. https://alevelchemistry.co.uk/notes/halogens/
  7. https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Supplemental_Modules_and_Websites_(Inorganic_Chemistry)/Descriptive_Chemistry/Elements_Organized_by_Block/2_p-Block_Elements/Group_17%3A_The_Halogens/0Group_17%3A_Physical_Properties_of_the_Halogens/Group_17%3A_General_Properties_of_Halogens
  8. https://www.vedantu.com/chemistry/group-17-elements

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