Now, you have quite some idea about the periodic table. Have you heard about the ‘halogen‘ lights? Yes, the ones that you use in your garden, maybe? But, do you know that the Group 17 elements in the periodic table are called “halogens”. Why? Well, we will find out soon! In this chapter, we will cover all about halogens, their properties, and uses.
Group 17 Elements
The group 17 elements include fluorine(F), chlorine(Cl), bromine(Br), iodine(I) and astatine(At) from the top to the bottom. They are called “halogens” because they give salts when they react with metals. So, now you know what halogens are! Let’s now look at the electronic configuration of these elements.
Electronic Configuration of Group 17 Elements
The valence shell electronic configuration of these electrons is ns2np5. Thus, there are 7 electrons in the outermost shell of these elements. The element misses out on the octet configuration by one electron. Thus, these elements look out to either lose one electron and form a covalent bond or gain one electron and form an ionic bond. Therefore, these are very reactive non-metals.
Let us now look at the various atomic properties of the group 17 elements. We will speak about the ionic and atomic radii, ionization enthalpy and more.
1) Ionic and Atomic Radii
The nuclear and atomic radii of these elements keep on increasing as we move down the group. This happens because of the addition of an extra energy level. They have the minimal atomic radii compared to the other elements in the related periods. This can be attributed to the fact that their atomic charge is quite powerful.
2) Ionisation Enthalpy
These elements have higher ionization enthalpy. This value keeps on diminishing as we move down the group. This happens because of the increase in the size of the nucleus. However, it is interesting to note that fluorine has the highest ionization enthalpy than any other halogen, thanks to its minute size!
3) Electron Gain Enthalpy
The electron gain enthalpy of these elements becomes less negative upon moving down the group. Fluorine has lesser enthalpy than chlorine. We can attribute it to the small size and the smaller 2p sub-shell of the atom of fluorine.
The halogens exhibit high electro-negativity values. However, it diminishes slowly on moving down the group from fluorine to iodine. this can be attributed to the increase in nuclear radii upon moving down the group.
Learn more about Group 16 Elements here.
Let us now look at the various physical properties of these halogens.
- Physical state: The group 17 elements are found in diverse physical states. For example, Fluorine and Chlorine are gases. On the other hand, Bromine is a liquid and Iodine is solid.
- Colour: These elements have a variety of colours. For example, while Fluorine is pale yellow in colour, Iodine is dark violet in colour.
- Solubility: Florine and Chlorine are soluble in water. On the other hand, Bromine and Iodine are very less soluble in water.
- Melting and boiling points: Melting and boiling points of these elements increase as we move down the group from Fluorine to Iodine. Thus, Fluorine has the lowest boiling and melting points.
We will now have a look at some of the chemical properties of these elements.
1) Oxidising Power
All the halogens are great oxidizing agents. Of the list, fluorine is the most powerful oxidizing agent. It is capable of oxidizing all the halide particles to halogen. The oxidizing power reduces as we move down the group. The halide particles also act as reducing agents. However, their reducing capacity decreases down the group as well.
2) Reaction with Hydrogen
All halogens react with hydrogen and produce acidic hydrogen halides. The acidity of these hydrogen halides reduces from HF to HI. Fluorine reacts violently and chlorine requires the sunlight. On the other hand, bromine reacts upon heating and iodine needs a catalyst.
3) Reaction with Oxygen
Halogens react with oxygen to form oxides. However, it has been found that the oxides are not steady. Beside oxides, halogens also form a number of halogen oxoacids and oxoanions.
4) Reaction with Metals
As halogens are very reactive, they react with most of the metals instantly and form the resulting metal halides. For example, sodium reacts with chlorine gas and forms sodium chloride. This process is an exothermic one and gives out a bright yellow light and a lot of heat energy.
2Na(s) + Cl2(g) → 2NaCl(s)
Metal halides are ionic in nature. This is because of the high electronegative nature of the halogens and high electropositivity of the metals. This ionic character of the halides reduces from fluorine to iodine.
Learn more about s-Block Elements here.
Solved Example for You
Q: Mention some uses of halogens.
Ans: The uses of halogens are:
- Fluorine compounds constitute an important ingredient in toothpaste. This is because fluoride compounds react with the enamel of the teeth and take care of teeth rotting.
- Chlorine majorly used as a bleach. It is also used in the metallurgy of elements like platinum and gold.
- Iodine is used as an antiseptic because it kills the germs on the skin.