Halogens - Trends In Chemical And Physical Properties

The group 17 of the modern periodic table consists of:

  • Fluorine

  • Chlorine

  • Bromine

  • Iodine

  • Astatine

These elements are known as the halogens. The word Halogen is a Greek word which means salt producer. These elements are called salt producers because chlorine, bromine, and iodine are highly electronegative in nature and form anions that constitute the anionic part of salts found in the seawater. The last element of the group, astatine is radioactive in nature. All these elements belong to the p block of the modern periodic table. After the alkali group, the halogen family constitutes the most homogenous group in the modern periodic table.

Halogens Trends In Chemical And Physical Properties

Physical and Chemical Properties of Halogens

Halogens show very smooth variations in their physical properties. Fluorine and chlorine are in the gaseous state, bromine in liquid and iodine in the solid state. The melting and boiling point of halogens increases with increase in the atomic number of the element. All the members of the halogen family are coloured. This happens due to the absorption of the radiation in the visible region which results in the excitation of the electrons in the outer shell to higher energy levels. They absorb different quanta of radiation, hence display different colours. We have fluorine which is yellow, chlorine is greenish yellow, bromine is red and iodine is violet. Fluorine and chlorine react with water. Bromine and iodine are sparingly soluble in water but are highly soluble in other organic solvents such as chloroform and carbon disulphide.

The halogens generally exhibit -1 oxidation state but chlorine, bromine, and iodine also exhibit +1, +3, +5 and +7 states. The higher oxidation state of halogens is obtained only when they are in combination with highly electronegative atoms of fluorine and oxygen. The halogens are highly reactive in nature. They often react with metals and non-metals to form halides. The reactivity of halogen family decreases as we move down the group. Halogens readily accept electrons as they are short of one electron to form an octet. Hence, they have strong oxidizing nature. Fluorine is the strongest oxidizing agent in the halogen family and it oxidizes other halide ions in the solution.

Period Element Symbol Atomic Number Electronic Configuration
2 Fluorine Fl 9 [He] 2s2p5
3 Chlorine Cl 17 [Ne] 3s3p5
4 Bromine Br 35 [Ar] 3d10 4s4p5
5 Iodine I 53 [Kr] 4d10 5s5p5
6 Astatine At 85 [Xe]4f14 5d10 6s6p5

Frequently Asked Questions – FAQs


Why halogens are coloured?

Halogens are coloured because they take in radiations from the visible spectrum. This excites the valence electrons to a higher energy level. The amount of energy required for excitation differs from halogen to halogen, thus they exhibit different colours.

Why are halogens strong oxidising agents?

Halogens have an electronic configuration of np5, where n =2 to 6. Thus, halogens require only one more electron to complete their octet and to attain the stable noble gas configuration. Moreover, halogens have high negative electron gain enthalpies and are highly electronegative with low dissociation energies. As a result, they have a high tendency to gain an electron. Hence, they act as strong oxidising agents.

What elements are called halogens?

Fluorine, Chlorine, Bromine, Iodine and Astatine are called halogens.

Which halogen is radioactive?

Astatine is a radioactive element belonging to the halogens group.

Which halogen is a liquid at room temperature?

Bromine is a liquid at room temperature.
Give an example of an interhalogen compound.
IF7 is an example of an interhalogen compound.

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