Group 7, The Halogens | A Level Chemistry | OCR, AQA, Edexcel

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This week we are revising Group 7, The Halogens

A-Level Chemistry can be tough but fortunately we’ve made this tutorial to help you score the A* you need for questions on everything to do with Group 7, The Halogens.

Elements in Group 7 are collectively known as the halogens.
Group 7 elements are all non-metals and exist as diatomic molecules. In each molecule, two atoms of the element are held together by a single covalent bond. Adjacent diatomic molecules have weak London forces between them.

Halogen atoms have 7 electrons in their outermost shell. The electron configuration of their outermost shell is always s2 p5. In order to achieve the stable electron configuration of a noble gas they only need to gain one electron to form a 1- ion. As a result, they are very reactive elements.
As you move down Group 7, the boiling points of the elements increases. As you move down Group 7, the van der Waals forces become stronger as the size of the Group 7 molecules increases. As learned earlier, the bigger the molecule, the more electrons are present therefore the stronger the van der Waals forces. The trend in boiling points is represented by the changes in the physical states of the halogens from gas to solid.

As you move down Group 7, the melting points of the elements increases. Once again, this is due to increased strength of Van der Waals forces between halogen molecules.

As you move down Group 7, the volatility of the elements decreases. Volatility refers to the ability of a substance to turn from a solid directly into a gas. Do to the weak Van der Waals forces between diatomic molecules, halogens have relatively low volatility points, and the higher up the group you are, the lower this volatility point will be.

Bond energies in diatomic molecules of halogens are relatively low. Low bond energies mean that the covalent bonds in the diatomic molecules are weak and hence easy to break.

As you move down the group, bond energies decrease. The atomic radius of the elements increases down the group so there is an increased shielding effect. This means that there is a reduced attraction between the nucleus of the halogen atoms in the diatomic molecule and the shared pair of electrons in the covalent bond. As a result, the covalent bond in the the diatomic molecule weakens as you go down the group.

As you move down Group 7, the electronegativity of the elements decreases. All halogens are very electronegative with fluorine being the most electronegative element. As you move down the group, the atomic radius of the elements increases and there is an increased shielding effect. This means that there is a reduced attraction between the the halogen atoms and atoms of other elements, forming bonds less readily.

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