Beginner Topic 659 of 1102 Inorganic Chemistry
Halogens
Group 17 elements are reactive diatomic nonmetals, ranging from gaseous F2 and Cl2 to solid I2.
In-depth explanation of Halogens
The halogens, fluorine, chlorine, bromine, iodine and astatine, form Group 17 and have seven valence electrons in the ns2 np5 configuration. They are the most electronegative elements in their periods and exist as coloured diatomic molecules, X2. Fluorine is pale yellow, chlorine green-yellow, bromine red-brown, and iodine is a violet solid that sublimes to a purple vapour. Melting and boiling points rise down the group because the molecules have more London dispersion forces, so fluorine and chlorine are gases, bromine a liquid and iodine a solid. They readily gain one electron to form halide ions.
Going deeper: Halogens
Key ideas: Group 17 ns2 np5: F, Cl, Br, I, At. Physical states: F2 and Cl2 gases, Br2 liquid, I2 solid. Bond dissociation energy is highest for Cl2 (242 kJ per mol), not F2 (158), due to lone pair repulsion in small F2. Oxidizing power: F2 greater than Cl2 greater than Br2 greater than I2, E0 +2.87, +1.36, +1.07, +0.54 V. Chlorine has the most negative electron gain enthalpy, about -349 kJ per mol.
Common mistakes and connections: Students think F has the highest electron affinity; Cl does, as F is so small that electron repulsion intervenes. F shows only -1, whereas other halogens show +1, +3, +5, +7 in oxoacids. Disproportionation of Cl2 in base: 3Cl2 + 6OH- gives 5Cl- + ClO3- + 3H2O hot. Links to periodic trends, interhalogens and bleaching powder.
Visualization of Halogens
Boiling points of the halogens (85, 239, 332 and 457 K) rise down the group as London dispersion forces strengthen: gases, liquid, then solid. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Chlorine gas is green-yellow, while iodine sublimes to a violet vapour when heated.
Frequently asked questions about Halogens
What is Halogens?
Group 17 elements are reactive diatomic nonmetals, ranging from gaseous F2 and Cl2 to solid I2.
Is Halogens a beginner, intermediate or advanced topic?
Halogens is a beginner topic in Inorganic Chemistry. It needs no earlier chemistry lessons and is a good starting point.
What should I learn before Halogens?
Study these earlier topics in Inorganic Chemistry first: Sulfur Allotropes, Sulfur Dioxide, Sulfuric Acid.
What comes after Halogens?
The next topics in Inorganic Chemistry are Halogen Reactivity Trend and Hydrogen Halides.
Can I practise Halogens with quizzes?
Yes. The interactive lesson includes a self-check question on Halogens, and the Inorganic Chemistry quiz draws on every topic in this area.
Where Halogens fits in Inorganic Chemistry
Halogens is topic 44 of 113 in Inorganic Chemistry.