Atomic and Physical Properties of Group 17 Elements: The elements are classified into four blocks in the long form of the periodic table: \({\rm{s,}}\,{\rm{p,}}\,{\rm{d}}\), and \({\rm{f}}\), depending on the subshell into which the last electron enters. The elements in the periodic table’s s and \({\rm{p}}\) blocks are representative elements or main group elements. Elements in groups \(1\) and \(2\) belong to the \({\rm{s}}\)-block, while elements in groups \(13\) to \(18\) belong to the \({\rm{p}}\)-block.

Fluorine is a highly electronegative element and belongs to the halogens group. Many other elements have general characteristics like fluorine. This article will study all about a group’s atomic and physical properties in the \({\rm{p}}\)-block, group \(17\), or Halogens.

Group 17 Elements

Group \(17\) is included in the \({\rm{p}}\)-block of the periodic table and consists of five elements: fluorine \(\left( {\rm{F}} \right)\), chlorine \(\left( {\rm{Cl}} \right)\), bromine \(\left( {\rm{Br}} \right)\), iodine \(\left( {\rm{I}} \right)\), and astatine \(\left( {\rm{At}} \right)\).

This group is commonly known as halogens. Halogens are derived from two Greek words: halo, sea salt, and gens, which means the product, i.e., sea salt products. This is because the first three members exist as salts in seawater. These are some of the most reactive non-metal elements. The last member of the family- astatine, is a radioactive element.

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Occurrence of Group 17 Elements

The halogens are very reactive in nature and, therefore, do not occur in the state. Except for astatine, all other elements are abundant in the earth’s crust as halide ions.

Halogens can be found in all three states of matter.

Fluorine is the \({\rm{1}}{{\rm{3}}^{{\rm{th}}}}\) most abundant element in the earth’s crust by weight. At room temperature, it exists in the gaseous state. It is most commonly found as insoluble fluorides, cryolites, fluorspar, and fluorapatite. Fluorine can also be found in soil, plants, stream water, and animal bones and teeth.

Chlorine is the \({\rm{2}}{{\rm{0}}^{{\rm{th}}}}\) most abundant element in the earth’s crust by weight. At room temperature, it exists in the gaseous state. The ocean’s water contains \({\rm{1}}{\rm{.5\% }}\) sodium chloride by weight.

Chlorine, bromine, and iodine can be found in ocean water as chlorides, bromides, and iodides of highly reactive metals such as sodium, potassium, magnesium, and calcium.

Ocean water contains trace amounts of iodides. Ocean weeds and crude chile saltpetre are the primary sources of iodine.

Astatine is a naturally occurring radioactive element and exists as a solid at room temperature.

Trends, Atomic and Physical Properties of Group 17 Elements

Electronic Configuration of Group 17 Elements

The elements in Group \(17\) have \(7\) electrons in their valence shell and have the following general electronic configuration: \({\rm{n}}{{\rm{s}}^2}{\rm{n}}{{\rm{p}}^5}\).

Atomic and Ionic Radii of Group 17 Elements

The halogens have the smallest atomic radii in their respective periods due to the maximum effective nuclear charge. The atomic and ionic radii increase as the atomic number increases. This is because the number of electron shells has increased. As the halogen atom forms the halide ion by gaining one electron, so radius of the halide ion is always greater than that of the corresponding halogen atom.

Ionisation Enthalpy of Group 17 Elements

These elements have high ionisation enthalpy. As a result, these elements have a very less tendency to lose electrons. The value of ionisation energy decreases as we move down the group. This is due to the steady increase in atomic size, which reduces the attraction between the valence electrons and the nucleus.

Fluorine has a much higher ionisation enthalpy than any other halogen due to its small size.

Electron Gain Enthalpy of Group 17 Elements

Moving down the group, the electron gain enthalpy becomes less negative. This is because the effect of increasing atomic size is much greater than the effect of increasing nuclear charge, and thus the additional electrons feel less attraction by the nucleus in the large atom.

The negative electron gain enthalpy of fluorine is lower than that of chlorine. Therefore, chlorine has the most negative electron gain enthalpy. It is due to the very small size of fluorine. As a result, the approaching electron encounters a greater degree of repulsion from the already present electrons.

Electronegativity of Group 17 Elements

Halogens have a high electronegativity. As the atomic size increases and the effective nuclear charge decreases, the value of electronegativity decreases down the group from fluorine to iodine.

Fluorine is considered to be the most electronegative element in the periodic table.

Melting and Boiling Points of Group 17 Elements

The melting and boiling points of halogens increase as we move down the group because of increased atomic size because a higher atomic size atom has a high Van der Walls force of attraction.

Fluorine has the lowest melting and boiling points.

Metallic Nature of Group 17 Elements

All of these elements are nonmetallic due to their high ionisation enthalpy values. On moving down the group, the metallic nature of elements increases, and the nonmetallic nature decreases.

Oxidation States of Group 17 Elements

Group \(17\) has a general electronic configuration: \({\rm{n}}{{\rm{s}}^2}{\rm{n}}{{\rm{p}}^5}\).

All elements of group \(17\) have \(7\) electrons in their valence shell. To complete their octet, these elements require one electron. They can complete their octet by either gaining or sharing an electron. All of the elements in this group have oxidation states of \(-1\).

Except for fluorine, the valence shells of bromine, chlorine, and iodine contain vacant \({\rm{d}}\)-orbitals. As a result, they have different oxidation states such as \(+ {\rm{ }}1, + {\rm{ }}3, + {\rm{ }}5, + {\rm{ }}7\), and \(-1\). Oxoacids, interhalogens, and oxides are examples of positive oxidation states.

Physical State of Group 17 Elements

Fluorine and chlorine are present in the gaseous state. Bromine exists in liquid form. Iodine exists in solid form. All of these elements can be found as diatomic molecules.

Colour of Group 17 Elements

The colour of halogens is caused by their molecules absorbing visible light radiations and the outer electrons easily being stimulated to higher energy levels.

Solubility of Group 17 Elements

Water dissolves fluorine and chlorine. Organic solvents dissolve bromine and iodine.

Density of Group 17 Elements

As the atomic mass increases down the group, the density increases.

Below given is the table showing the density of halogens in \({\rm{g}}/{\rm{c}}{{\rm{m}}^3}\).

Bond Dissociation Energy of Group 17 Elements

Except for fluorine, the bond dissociation energy decreases as we move down the group. Because of its small atomic radius, fluorine has a low bond dissociation energy.

Anomalous Behaviour of Fluorine

Fluorine’s valence shell exhibits anomalous behaviour in properties such as ionisation energy, bond dissociation energy, electronegativity, electrode potentials, ionic and covalent radii, electron gain enthalpy, melting point, and boiling point due to its small nuclear size, high electronegativity, low bond separation energy, and lack of accessibility of \({\rm{d}}\)-orbitals.

Uses of Group 17 Elements

1. Fluorine compounds are used in toothpaste and some drinking water supplies because they react with tooth enamel and prevent tooth decay.
2. Chlorine is used for bleaching, in the metallurgy of gold and platinum, and in the formation of natural halogen compounds.
3. Chlorine is used in the purification of drinking water.
4. Bromine is used to treat pneumonia and Alzheimer’s disease.
5. Iodine is used as an antiseptic because it kills germs on the skin without harming the skin itself.
6. Astatine is radioactive and is used to study cancer.

Summary

In this article, we studied that halogens can occur in all three states and have a general electronic configuration \({\rm{n}}{{\rm{s}}^2}{\rm{n}}{{\rm{p}}^5}\). We also studied the following points:

1. The atomic number, atomic mass, density, and melting and boiling point increase down the group.
2. Ionisation enthalpy and electronegativity decrease down the group.
3. All the halogens are coloured.

FAQs on Atomic and Physical Properties of Group 17 Elements

Q.1. What are the physical properties of group 17 elements?
Ans: Some of the physical properties of group \(17\) are as follows:
1. The atomic and ionic radii increase as we go down the group.
2. The ionization enthalpies of the elements decrease on moving down the group.
3. The electron gain enthalpy decreases as the atom’s size increase down the group.
4. The melting and boiling points increase as the atomic size increases from fluorine to astatine.
5. All the elements of this group are non-metals.
6. The elements in group \(17\) show an oxidation state of \( + {\rm{ }}1, + {\rm{ }}3, + {\rm{ }}5, + {\rm{ }}7\), and \(-1\). Fluorine shows an oxidation state of \(-1\) only.

Q.2. Which properties decrease with the increasing atomic number in group 17?
Ans: Ionisation enthalpy and electronegativity decrease down the group as the atomic number increases.

Q.3. What are the uses of halogens?
Ans: Some of the uses of halogens are as follows:
1. Fluorine is used in drinking water and toothpaste because it helps to prevent tooth decay. It can be found in the clay used in ceramics.
2. Chlorine is used in the purification of drinking water and swimming pools.
3. It is also used to sterilise hospital equipment.
4. Bromine has fire-resistance properties, so it is used as a fire extinguisher to retard flames.
5. Iodine is used as an antiseptic because it kills germs on the skin while causing no harm to the skin.
6. Astatine is a radioactive substance that is used in cancer research.

Q.4. What are group 17 elements called?
Ans: The group \(17\) elements are called halogens.

Q.5. Name the elements of group 17 elements?
Ans: Group \(17\) is included in the \({\rm{p}}\)-block of the periodic table and includes five elements: fluorine \(\left( {\rm{F}} \right)\), chlorine \(\left( {\rm{Cl}} \right)\), bromine \(\left( {\rm{Br}} \right)\), iodine \(\left( {\rm{I}} \right)\) and astatine \(\left( {\rm{At}} \right)\).

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