Periodic Table of Elements

Halogens

The halogens are located in Group 17 (VIIA) of the periodic table and belongs to a class of nonmetals. The halogen elements are fluorine, chlorine, bromine, iodine, astatine, and ununseptium. Ununseptium is artificially created element. The term "halogen" means "salt-former" and compounds containing halogens are called "salts".

Properties of halogens:

The halogens exist in all three states of matter at standard temperature and pressure:
  • Solid- Iodine, Astatine
  • Liquid- Bromine
  • Gas- Fluorine, Chlorine
All halogens have 7 valence electrons in their outer shells, giving them an oxidation number of -1. Halogens lack only one electron to form a complete shell.
All of the halogens are components of acids.
They form diatomic molecules in the pure state.
The halogens are also all toxic.
Halogens have very high electronegativities. Their electronegativity decreases down group from fluorine to astatine (refer to the table below for supporting data).
Halogens are highly reactive, especially with alkali metals and alkaline earths.
Halogens are extremely active chemically. Chemical activity increases as you move upward in the group, fluorine being the most active element in the periodic table.
Their boiling Point increases down group from fluorine to astatine (refer to the table below for supporting data)
Their atomic size increases down group from fluorine to astatine (refer to the table below for supporting data).
Their ionic size increases down group from fluorine to astatine (refer to the table below for supporting data).
Interhalogens : Compounds composed of two or more different halogen atoms are called as interhalogens. For ex. Chlorine trifluoride, Iodine heptafluoride
Physical and atomic properties of halogens:
Property Standard atomic weight (unified atomic mass unit) Melting point (K) Melting point (°C) Boiling point (K) Boiling point (°C) Density (g/cm3 at 25 °C) Electronegativity (Pauling) First ionization energy (kJ·mol-1) Covalent radius (pm)
fluorine 18.998403253.53-219.6285.03-188.120.00173.981681.071
chlorine 35.446171.6-101.5239.11-34.040.00323.161251.299
bromine 79.904265.8-7.3332.058.83.10282.961139.9114
iodine 126.90447386.85113.7457.4184.34.9332.661008.4133
astatine 209.99575302? 610? 337?2.2? 887.7?
Chemical properties of halogens:
Element Symbol Atomic number No. of electrons/shell
fluorine F 9 2, 7
chlorine Cl 17 2, 8, 7
bromine Br 35 2, 8, 18, 7
iodine I 53 2, 8, 18, 18, 7
astatine At 85 2, 8, 18, 32, 18, 7
ununseptium Uus 117 2, 8, 18, 32, 32, 18, 7 (predicted)
Uses of halogens and halides:
Halogens and halides Uses
Fluorine, F2
  • CFC’s
  • polymers
  • non-stick frying pans, electrical insulation, waterproof clothing
Fluoride, F-
  • helps prevent tooth decay - tin fluoride is added to toothpaste
  • sodium fluoride is added to water supplies
  • Hydrogen fluoride, HF - and used in petrolium industry
  • Sulfur hexafluoride SF6 – used as an electrical insulator
Chlorine, Cl2
  • used in water purification
  • used as bleach
  • used as solvent
  • used to make polymers

  • used to make CFC’s
  • chlorine oxides are used as bleaching agent in paper industry
Bromine
  • used as an additive in leaded gasoline
  • used in dyes, disinfectants, and photographic chemicals.
Silver bromide, AgBr used in photographic films and plates
Iodine
  • used as germ killer
  • used in antiseptics drugs, dyes, specialized soaps and photographic films.
  • used as a catalyst
Silver iodide, AgI used in photochemicals and cloud seeding
Astatine used as a radioactive tracer