Halogens - Trends in Chemical and Physical Properties

Group 17 Trends Properties

The modern periodic table's group 17 consists of the following elements.

• Chlorine

• Fluorine

• Iodine

• Bromine

• Astatine

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

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What are Halogens?

Halogens belong to group 17 of the periodic table. Halogens are highly reactive non-metals and have a great resemblance in their properties. Collectively, the Group 17 elements are called halogens (In Greek, the halo is described as salt, genes - means producing, so collectively it can be given as salt-producing). These elements are chlorine, fluorine, bromine, astatine, and iodine.

Besides, a similarity to this extent is not found in the other groups of the modern periodic table. They exhibit a regular gradation in both physical and chemical properties. In this group, astatine is the only radioactive element. Halogens have 7 electrons in their outermost shells (ns2np5), and they are short of 1 electron from the nearest noble gas configuration. An element's reactivity and chemical properties are determined by the oxidation state exhibited by it.

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Physical and Chemical Properties of Halogens

Let us look at a few physical and chemical properties of halogens.

Physical Properties of Halogens

A few physical properties of group 17 halogens can be listed as follows.

• Halogens exhibit very smooth variations towards their physical properties.

• Chlorine and Fluorine are in the gaseous state, whereas bromine is in the liquid state and iodine is in the solid-state.

• The melting and boiling points of the halogens increase with an increase in their atomic numbers.

• All the members of the halogen family are coloured, due to the absorption of the radiation in the visible region, resulting in the excitation of the valence electrons to higher energy levels.

• These elements absorb different quanta of radiation; thereby, they display multiple colours. We have fluorine- yellow, bromine- red, chlorine- greenish-yellow, and iodine- violet.

• Chlorine and fluorine react with water. Iodine and bromine are sparingly soluble in water, but they are highly soluble in other organic solvents such as carbon and chloroform disulfide.

Chemical Properties of Halogens

Generally, halogens exhibit a -1 oxidation state, but, bromine, chlorine, iodine exhibit +1, +3, +5, +7 states. The halogens' higher oxidation state is obtained only when they are in combination with highly electronegative atoms of oxygen and fluorine. Halogens are also highly reactive in nature, and they often react with metals and non-metals forming halides.

The reactivity of the halogens decreases as we move down from the group. Also, halogens readily accept electrons since they are short of 1 electron to form an octet. Thus, they exhibit a strong oxidizing nature. In the halogen family, fluorine is the strongest oxidizing agent, and it oxidizes other halide ions of the solution.

Trends of Electronegativity in the Periodic Table among Halogens

Electronegativity can be described as the ability of an atom to attract other electrons. Atoms that exhibit high electronegativities have the capacity to attract more electrons and can gain electrons from the other atoms while forming chemical bonds. Atoms having low electronegativities tend to share electrons in a bond.

• The relative tendency of an atom in a chemical bond to attract the shared electron pair towards itself is defined as its electronegativity.

• In a period, halogens are the most electronegative of all the other elements because of their small atomic size and high nuclear charge.

• Their non-metallic and electronegative nature gradually decreases down the group with an increase in their atomic size.

The values of electronegativity of the halogens can be given as follows.

• F = 4,

• Br = 2.8,

• Cl = 3,

• I = 2.5.

Did you know

Why is the Electron Affinity of Chlorine More than that of Fluorine?

This is due to the compact structure of fluorine. Chlorine has a larger atomic size hence it can accommodate more electrons, whereas the electrons in fluorine are closely-spaced. So, the crowded electrons in fluorine screen its effective nuclear charge, and thus, it exhibits a lower electron affinity.

What is Meant by the Pseudo Halogens?

Pseudo halogens are the groups that are formed by the combination of either two or more P block elements of the periodic table with a unit negative charge. For example, CN-, a cyanide group, a combination of carbon, nitrogen holding a unit-negative charge. They are known as pseudohalogens because they produce covalent compounds and complexes, same as halogens, in the periodic table. They differ from halogens because they can polymerise unlike halogens, and their complexes are not paramagnetic.