Group 17 Elements for IIT JEE

The electronic configuration of valence shell is ns² np⁵ which means that there are 7 electrons in the outermost shell and it requires one more electron to complete its octet. It can either lose one electron to form a covalent bond or it can gain one electron and form an ionic bond. Due to this reason it is said to be very reactive in nature.

1) Electronegativity

As we move down the group, the electronegative values decrease since it depends on the strength of the bonding energy between the outermost electrons and nucleus. While going down the group, the nuclei radius increases indicating that the outermost electrons gets farther from the nucleus, thus bonding gets weaker. Fluorine being the first element has small radius indicating that the electrons are closely attached to the nucleus, thereby the electronegativity is high. Iodine has more shells keeping the outermost electrons far away from nucleus reducing the bond energy between them and thereby the electronegativity is low.

The arrangement of electronegativity is F> Cl> Br> I

2) Atomic and ionic radii

As we go down the group, the atomic radii and ionic radii increase. This is because there is an increase in the number of shells as we go down the group. There is another reason being that the atomic charge decreases as we go down the group. The series is F< Cl< Br< I

3) Ionization energy

As we move down the group, the number of shells increases wherein the diameter or size of the nucleus increases. Due to this, the ionization enthalpy decreases as we move down. In other words, it means, that the bonding energy between the nucleus and the outermost electrons decrease, wherein less energy is needed to pull out the outermost electrons. But fluorine has highest ionization enthalpy as its size is small wherein the electrons are held strongly to the nucleus. The series is F> C> Br> I

4) Electronic gain enthalpy

As we go down the group, the electron gain enthalpy becomes less negative. For example, Fluorine at the top of the group has lesser enthalpy than chlorine, though fluorine is more electronegative. This is due to the reason that the size of the atom of fluorine is small and the size of 2p shell is small. Here, the addition of electron is not favored as electron repulsion is more intense. 

The series is F< Cl< Br< I

5) Electron affinity

As we go down the group, the atomic radius increases and the outermost electrons have less attraction with the nucleus. Hence, the electron affinity decreases as electronegativity decreases since the forces of electron pull is lessened. The series is Cl> F> Br> I

6) Reactivity of elements

As we go down the group, the reactivity decreases as there is an increase in the atomic radii with an increase in the number of energy shells. Due to this, there is decreased forced of attraction between the outermost electrons and nucleus.
The series is F> Cl> Br > I

1) Colour: These elements exhibit a variety of colors like fluorine exhibits pale yellow color while iodine exhibits dark violet color.

2) Physical nature: Fluorine and Chlorine are found to be in gaseous form while bromine is in liquid form and iodine is found in the solid form.

3) Solubility in water: Fluorine and Chlorine are soluble in water while bromine and iodine are less soluble in water.

4) Boiling point: The boiling point of these elements increases as we move down the group due to the Van der Waal forces. Going down the group, the molecular size increases, indicating that the Van der Waals forces also increase thereby making it difficult to break down the molecules. When considering the elements, fluorine has the lowest boiling point.

The series is F< Cl< Br< I

5) Melting point: The melting point of group 17 elements increases as we go down the group. This is due to the increased molecular size wherein the Van der Waals forces become stronger. Thus, making it difficult to break the bonds. Hence, Fluorine has the lowest melting point.

The series is F< Cl< Br< I

1) Action on Hydrogen: The halogens produce hydrogen halides when it reacts with hydrogen. The reactivity of these elements is such that fluorine reacts violently while chlorine reacts in the presence of sunlight. Bromine reacts only on heating while iodine requires a catalyst to produce halides.

The compounds formed are HF, HBr, HCl, HI.

2) Action on oxygen: The halogens react with oxygen to form oxides

3) Oxidizing nature: The halogens are said to be good oxidizing agents with first element fluorine being the most powerful that can oxidize all other halides. But the oxidizing power reduces as we go down the group.

4) Action on metals: As other properties, halogens react instantly with metals forming its halides. Example: Reaction of sodium with chlorine gives sodium chloride giving out bright yellow light and heat.

2Na (s) + Cl₂(g) 2NaCl (s) + Heat

As the halogens are electronegative and metals are electropositive, the metal halides are ionic in nature. Fluorine being more electronegative shows strong ionic bonds and the ionic nature reduces as we go down the group.