Group 17 Elements: Properties, Electronic Configurations and Reactions

Group 17 elements, also known as halogens, are fluorine, chlorine, bromine, iodine, and astatine. These are naturally occurring elements (except Tennessine, which is created artificially) and resemble each other in properties like no other groups of the periodic table. Astatine is the only radioactive element in the group. 

Group 17 is the fifth group in p block. The electronic configuration is ns²np⁵. The word halogen means salt producers. This group generally has -1 oxidation state. The oxides of these halogen can be formed but they are not stable.

Key Terms: Electronic configuration, Elements, Halogens, Electronegativity, Acids, Melting and Boiling points, Ionization charge

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What are Group 17 elements?

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Halogen are present in  diatomic form when in the elemental state. The bonds between these atoms are nonpolar covalent single bonds. But they are highly reactive and among the halogens, fluorine is the most reactive.

• This property of reactivity is attributed to the seven electrons in the last shell and now they need only one electron to complete the octet.  
• Group 17 elements are the elements that can exist in three states of matter at room temperature; solid, liquid, and gases.
• The elements are particularly non-metals and can be found on the right-hand side of the periodic table.
• These elements are highly electronegative- fluorine being the most- highly reactive and have a tendency to form salts when reacting with metals. 

Modern Periodic Table

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Electronic Configuration of Group 17 elements

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The electronic configuration of each Group 17 element is mentioned below-

1. Fluorine (F) : 2s²²p⁵
2. Chlorine(Cl) : 3s²3p⁵
3. Bromine (Br) : 3d¹⁰4s²4p⁵
4. Iodine (I) : 4d¹⁰,5s²5p⁴
5. Astatine (At) : 4f¹45d¹⁰6s²6p⁴ 

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Characteristics of Group 17 elements

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The various characteristics of the group 17 elements such as the color, atomic size, and electronegativity are separately discussed below-

Atomic Size

It increases downwards with the group every time a new shell is added. When we compare the size of group 16 elements with that of group 17 we can see that group 17 elements are smaller because of the increased nuclear charge. F < Cl < Br < I < At

Ionization Charge

While comparing the ionization energy of Group 17 and Group 16, it is observed that Group 17 has higher energy than Group 16 because of the smaller size of the Group 17 elements. The electrons from the further shells can be easily removed without the need to much energy. 

Electronegativity

Group 17 elements are more electronegative than group 16 elements because of the small size of the Group 17 elements. This group has the highest electronegativity in the whole periodic table. In fact, Fluorine is the most electronegative element in the entire periodic table. As we go down in the group, electronegativity increases as the size decreases.

Melting and Boiling points

They increase down the group as the size and the mass increase, and the Vander wall force also increases therefore the melting and the boiling points also increase.

Colour

The color of the group 17 elements is listed below:

• Fluorine: Dull Yellow in color
• Chlorine: Yellowish Green
• Bromine: Reddish Brown
• Iodine: Violet

Oxidation states 

The elements of group 17 show an oxidation state as follows-

• Higher oxidation states of halogens are used when they are combined with small size highly electronegative ions.
• All Halogens are very reactive as a result of which reactivity decreases down the group.
• All exhibit properties of Lewis Acids as they accept electrons.
• Fluorine is the strongest oxidizing agent of all.

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Anomalous Properties of Fluorine

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f the properties of all the halogens are compared, Fluorine is observed to have some different properties. The reason for these anomalous properties are as follows: 

• It has high electronegative characters, the F-F bond dissociation enthalpy is low, hae small size and has high ionisation enthalpy. 
• F have the tendency to show mostly exothermic reactions. 
• Only one oxoacid of fluorine is known, while other elements have many oxoacids. 
• Fluorine atoms do not have a d orbital. 
• The hydrogenfluoride is liquid in state unlike other hydrogen halides. 

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Chemical Reaction of Group 17 Elements

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The chemical reaction of Group 17 elements with different elements are given below:

Reaction with Hydrogen 

The group 17 elements form their respective halogen acids of formula HX that is: Hydrogen Fluoride, Hydrogen Chloride, Hydrogen Bromide, and Hydrogen Iodide Some of the properties of halogen acids are-

• All halogens have a linear structure with a bond angle of 180 degrees.

Out of all these halogens, only Hydrogen Fluoride is liquid, the rest are gases.

The stability of Hydrides depends on the comparability of size. The order of stability of hydrides is - HF>HCl>HBr>HI 

Due to an increase in size, bond length increases due to which bond dissociation energy decrease therefore the stability decreases.

• The order of reducing nature of hydrides is - HF>HCl>HBr>HI

All are Arrhenius acids. The HI has the weakest bond as a result of which release of HI is much easier.

• Boiling point- HF>HCl

Due to Hydrogen bonding, HF has the highest boiling point.

• All halogen acids are polar in nature. The greater the size of an anion more is the more polarizability and the covalent character. Overall, HF is highly polar.

Reaction with Oxygen

The group 17 elements react with oxygen to form their respective oxides. Due to less electronegativity, the oxides are unstable. The oxides formed by them are the following-

• Fluorine- OF₂ and O₂F₂
• Chlorine- Cl₂O, ClO₂, Cl₂O₆, Cl₂O₇
• Bromine- Br₂O, BrO₂, BrO₃
• Iodine- I₂O₄, I₂O₅, I₂O₇

The order of stability of their Halides are - I>Br>Cl>F. This occurrence of this trend is owed to some thermodynamics reasons.

Oxy acids of HalogensThe Oxy acids of Halogens are:

• Fluorine- HFO(+1) Hypofluorous acid

• Chlorine-
• HClO (+1) Hypochlorous acid
• HClO₂ (+2) Chlorous acid
• HClO₃(+3) Chloric Acid
• HClO₄(+4) Perchloric acid
• Bromine-
• HBrO(+1) Hypobromous acid
• HBrO₃(+3) Bromic acid
• HBrO₄(+4) Perbromic acid
• Iodine-
• HIO (+1) Hypoiodous acid
• HIO₃ (+3) Iodic acid
• HIO₄(+4) Periodic acid

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Interhalogen Compounds 

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A compound of one halogen with another halogen is called an interhalogen compound. These are formed due to large electronegativity and the size difference between halogens. Example- Consider two halogens A and B. B is more electronegative than A and therefore they will form the following compounds-

• AB example: ClF (Chlorine monofluoride), BrF(Bromine monofluoride).
• AB3 example: ClF₃ (Chlorine trifluoride), BrF₃ (Bromine trifluoride).
• AB3 example: ClF₃ (Chlorine trifluoride), BrF₃ (Bromine trifluoride).
• AB7 example: IF₇ (iodine heptafluoride).

The interhalogen compounds are very reactive and unstable. Their properties are as follows;

• The larger halogen always serves as a central atom.
• They are strong oxidizing agents.
• The bonds formed are covalent.
• As the size difference decreases, stability decreases, and polarity increases.

Structure of interhalogen compounds

• AB type – linear
• AB3 type - trigonal bi pyramidal
• AB5 type - square pyramidal
• AB7 type - pentagonal bipyramidal