After Group 0 and Group 1, the next group in the GCSE syllabus is Group 7, also known as the halogen group. Like other groups, group 7 has its importance. Furthermore, elements of group 7 show different properties than other elements of different groups, making it more interesting. In this resource, you will learn about group 7 and its properties.
What is Group 7?
If you go to the far right of the periodic table, you will see group 0. Before group 0, group 7 exists. It is labelled with the Romanian 7 number, "VII". Group 7 have a unique name. We call it group 7 because they have seven electrons in their valance shell. They are also known as Halogens. Halogens are non-metals in nature and form salt when reacting with metals. "Halogen" means salt former; now you know why this group is also called halogen.
Halogens have unique physical and chemical properties that make them very special. Let's take a look at its physical and chemical properties.
Physical Properties
The first thing you will note about halogens is that they are coloured elements. Every element in group 7 has a different colour but with a trend that we will discuss in the next heading.
The melting points and boiling points of halogens are low. This is because the intermolecular forces are feeble. That means less energy is required to overcome those forces. You might be wondering why intermolecular forces are weak. That is because they exist at room temperature in a liquid or gas state. Liquids and gases have weak intermolecular forces, so halogens have low melting and boiling points.
At room temperature, fluorine and chlorine are gases, bromine is liquid, and astatine and iodine are solids.
Fluorine is pale yellow, chlorine is light green, and bromine is brown-red. The iodine colour is purple, and the astatine is dark black.
Physical Properties Trend
As you go down the group, you can observe a trend. Down the group, the melting and boiling points of halogens increase.
Another point to notice is that down the group, gases turn to liquid, and liquids turn to solids. For example, fluorine is a gas, bromine is a liquid, and iodine is a solid.
Last but not least, there is also a colour variation. As you move down the group, the colour of the halogens becomes darker. For example, fluorine is light, bromine is darker than fluorine, and astatine is the darkest.
Chemical Properties
Halogens are placed in group 7 because they have 7 electrons in their valance shell. That means they tend to accept a single electron to become stable. When they accept an electron, the overall balance of protons and electrons will break since electrons are more than protons. The electron's charge is -1; since there are more electrons, the charge on the whole atom will be -1. We call these charged particles ions. Hence, group 7 will always have a -1 charge in the ion state.
Displacement Reaction
Halogens undergo a displacement reaction. To understand this reaction, you need to learn the reactivity of halogens. As you move down the group, reactivity decreases. For example, fluorine is more reactive than iodine. In displacement reaction, the more reactive halogen replaces the less reactive halogen. For example:
NaCl + F → NaF + Cl
Fluorine just swapped places with chlorine in the above reaction. Can we say that fluorine displaced chlorine in the above reaction? That is why we call it a displacement reaction.
In the above reaction, fluorine is more reactive than chlorine. We know this because fluorine is above chlorine, and as reactivity decreases down the group, the reactivity of chlorine is less than fluorine. Therefore, fluorine displaces chlorine. Below is another example,
NaBr + Cl → NaCl + Br
Chlorine is more reactive than bromine, so chlorine displaces bromine to form sodium chloride. Check the equation below:
NaCl + I → No reaction
Nothing will happen in the above reaction because iodine is less reactive than chlorine; therefore, it will not displace chlorine.
Reactivity Series
The reactivity series says that down the group, reactivity decreases in halogens. This means that as we move down the group, the reactions of halogens will become slow and time-consuming.
This statement shows fluorine is the most reactive halogen, and astatine is the least reactive. This also means that fluorine can displace any halogen in the displacement reaction, and astatine cannot displace any halogen. In addition, halogens also undergo redox reactions, which you learn in detail in upcoming lectures.
Conclusion
Group 7 elements are one of the groups in the periodic table. It differs from other groups because of its physical and chemical properties.
Group 7 means that all the members in this group have seven electrons in their valance shell. Group 7 elements need to accept an electron to complete their valance shell. When they do, they will get a negative charge.
Elements of group 7 are non-metals and are coloured elements. They have low melting and boiling points because of weak intermolecular forces. Due to the unavailability of extra electrons, they are bad conductors of heat and electricity.
In addition, members of group 7 are reactive. They are readily available to react with metals. Down the group, they follow a trend in both properties, chemical and physical. The melting and boiling points down the group decrease, the state changes from gas to solid, colour becomes darker, and reactivity decreases.
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Thank you very much,you made me to understand in less than 20 minutes what I was unable to get during my secondary school days
Hi Dorcas! Thank you for your comment, great to hear that you found this resource helpful :)
Lithium is used in place of Fluorine
Hi Madan. You’re right to point that out – thanks very much for your comment!
amazing side
It’s very educative,I learnt alot thanks ❤️
Was very educative and help. Gave me a broader understanding of the topic