The Halogens

The Group with 7 Valence Electrons

Halogens are the elements in group 7A. Each Halogen has seven valence electrons.The group of halogens is the only periodic table group that contains elements in all three familiar states of matter at standard temperature and pressure.

Fluorine (F) - (diatomic nonmetal)                                       

  • Atomic number - 9
  • Mass number - 19
  • Protons and eletrons - 9
  • neutrons - 10
  • Atomic radius - 42 pm
  • ionization energy - 17,4228

Fluorine is a gas at room temperature.The melting point of fluorine is -219°C and a boiling point of -188°C.


Fluorine is used in toothpaste and drinking water to prevent tooth decay. Is also used to make teflon. Used to enhance rocket fuel.

Fluorine is used in refrigeration, air conditioning & insecticide.

What are the Physical Properties of Fluorine?

Color- It is a pale yellow, white or colourless gas.

Fluorescence- It can sometimes be fluorescent.

Solubility- In liquid form it is freely soluble in liquid oxygen and ozone.

Odor - Pungent.

Density- A density of 1.695 grams per liter, it is 1.3 times as dense as air.

Phase Change - Gas to liquid- Fluorine changes from a gas to a liquid at a temperature of -188.13°C (-306.5°F)

Phase Change - Liquid to solid- Fluorine changes from a liquid to a solid at -219.61°C (-363.30°F).

What are the Chemical Properties of Fluorine?

Fluorine is the most chemically active non-metallic element and is the most electro-negative of all the elements.

Chemical Formula- F.

Toxicity- Highly Poisonous at room temperature.

Oxidation- Does not combine with oxygen.

Compounds- The importance of fluorine lies largely in its compounds. Fluorite is used as a flux in refining iron. Cryolite is used in the production of aluminum.

Corrosion- Highly corrosive gas.

Reactivity with water- When mixed with water, it reacts explosively.

Reactivity with Elements- Reacts with all the elements except helium, neon, and argon.

Reactivity with heat- Heat resistant.

Flammability- Flammable, having the ability to catch on fire.

Bohr Diagram

Chlorine (Cl) - (diatomic nonmetal)

  • Atomic number - 17
  • Mass number - 35.453 ± 0.002 u
  • Protons and electrons - 17
  • Neutrons - 18
  • Atomic radius - 79 pm
  • Ionization energy - 12,9676

Chlorine is a gas at room temperature. Has a melting point of 101.5°C and a boiling point of -34.04°C.


Chlorine is an important chemical in water purification, in disinfectants, in bleach and in mustard gas.
Chlorine is also used widely in the manufacture of many products and items directly or indirectly, i.e. in paper product production, antiseptic, dyestuffs, food, insecticides, paints, petroleum products, plastics, medicines, textiles, solvents, and many other consumer products.
It is used to kill bacteria and other microbes from drinking water supplies.

What are the Physical Properties of Chlorine?

Color- Greenish-yellow.

Phase- Gas.

Odor- Disagreeable, suffocating smell.

Density- About two and one-half times as dense as air.

Solubility- Is soluble in water. Its aqueous solution is called chlorine water which consists of a mixture of chlorine, hydrochloric acid, and hypochlorous acid.

Boiling Point- The boiling point of chlorine is –34.05°C.

Melting Point- The melting point is –101°C.

What are the Chemical Properties of Chlorine?

Chemical Formula- Cl

Corrosion- Highly corrosive.

Toxicity- Highly Toxic.

Compounds- PVC, hydrochloric acid and Sodium chloride (table salt).

Reactivity with metals- Most metals react with dry chlorine only upon heating.

Combustion- Alkali metals react with chlorine by combustion when tiny amounts of moisture are present.

Explosive- Specific mixtures of chlorine and hydrogen can be explosive.

Oxidation- It forms the oxides Cl2O, ClO2, O2O6, Cl2O7, and Cl2O8, as well as hypochlorites (salts of hypochlorous acid), chlorites and chlorates.

Lewis Structure

Bohr Diagram

Bromine (Br) - (diatomic nonmetal)

  • Atomic number - 35
  • Mass number - 80
  • protons and electrons - 35
  • neutrons - 45
  • Atomic radius - 94 pm
  • Ionization energy - 11,8138

Discovered by Balard in 1826, but not prepared in quantity until 1860. Bromine is the only liquid nonmetallic element. Bromine is less active chemically than Chlorine and Fluorine but more active than iodine.

Is liquid at room temperature, with a boiling point of 58.8°C and a melting point of -7.2°C, and a density of 3.12 g/cm³.

Is corrosive to human tissue in a liquid state and its vapor irritate eyes and throat.

Physical Properties

  • Bromine is a red-brown liquid.
  • It easily evaporates to make suffocating brown fumes.
  • It has a bad smell.
  • It can become a metal at very high pressures.

Chemical Properties

  • Bromine is quite reactive.
  • It reacts with metals and nonmetals.
  • Bromine can form compounds with substances such as sodium to form sodium bromide.


Bromine is used in industry to make organobromine compounds. Bromine is used in making fumigrants dyes, flameproofing agents, water purification compounds, sanitizes, medicinals, agents for photography and in brominates vegetable oil, used as emulsifier in many citrus-flavoured solft drinks.

Lewis Structure

Bohr Diagram

Iodine (I) - (diatomic nonmetal)

  • Atomic number - 53
  • Mass number - 126.90447 u
  • Protons and electrons - 53
  • Neutrons - 74
  • Atomic radius - 115 pm
  • Ionization energy - 1008 kj mol-1

iodine is a solid at room temperature, with a melting point of 113.7°C and a boiling point of 184.3°C.


Iodine has many commercial uses including pharmaceuticals, photographic chemicals, printing inks and dyes, catalysts and animal feeds. Iodide in small amounts is added to table salt in order to avoid thyroid disease.

What are the Physical Properties of Iodine?

Color - Violet black. A sgray solid that changes into purple vapors when heated.

Luster - Has a shine or glow.

Odor - Strong, harsh odor.

Crystalline structure- Rhombic

Density - Heavy

What are the Chemical Properties of Iodine?

Chemical Formula - Hg

Toxicity - Poisonous halogen.

Oxidation - It does not combine directly with oxygen.

Compounds - With hydrogen it forms hydrogen iodide, which in water solution becomes hydriodic acid. Its compounds are used in medicine and photography and in dyes.

Corrosion - Highly corrosive

Reactivity with water - Dissolves only slightly in waterReactivity with heatMoves from the solid to the vapor state (sublimation).

lewis structure

Astatine (At) - (metalloid)

  • Atomic number -85
  • Mass number -210 u
  • Protons and electrons - 85
  • Neutrons - 125
  • Atomic radius - 145
  • Ionization energy - 920

Astatine is a solid at room temperature, with a melting point of 302°C  and a boiling point of 230°C

Physical Properties

Astatine is a highly radioactive element and it is the heaviest known
halogen. Its chemical properties are believed to be similar to those of iodine.
Is has been little researched because all its isotopes have short half lives.
All that is known about the element has been estimated from knowing its
position in the periodic table below iodine and by studying its chemistry in
extreme diluted solutions.


Astatine-211 is sometimes used as a radioactive tracer and in cancer

Bohr Diagram

Important Characteristics
All these elements are extremely reactive.
Due to this tendency towards high reactivity, the halogens cannot exist in the environment as pure elements. They are usually found occurring as compounds or as ions.
Most halogen ions and atoms can be found in combination with other compounds present in the sea or mineral water. This is because halogen elements tend to create salt when they come in contact with the metals and combine with them to form compounds.
All halogen elements form hydrogen halides, which are very strong acids, when they combine with hydrogen, and form binary compounds.
Halogens get their high tendency to react with other matter due to high levels of electronegativity of their atoms, which is a result of the high effective nuclear charge of all halogen atoms.

Henry Gwyn Jeffrey  Moseley (23 November 1887- 10 August 1915). Moseley's outstanding contribution to the science of physics was the justification from physical laws of the previous empirical and chemical concept of the atomic number. Moseley's Law justified many concepts in chemistry by sorting the chemical elements of the periodic table of the elements in a quite logical order based on their physics.

Dmitri Ivanovitch Mendeleev (1869) - Created the first accepted version of the periodic table.

  • Grouped elements on the basis of similar chemical properties.
  • Left blank spaces open to add new elements where he predicted they would occur.
  • Accepted minor inversions when placing the elements in order of increasing atomic mass.
  • Predicted properties for undiscovered elements, allowing for his theories to be tested.

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