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SQA Higher Chemistry The halogens

The halogens

This page covers the following topics:

1. Melting and boiling points of halogens
2. Electronegativity of halogens
3. Oxidising and reducing abilities of halogens

Halogens form small covalent molecules with the formula Xβ‚‚ held together by van der Waals forces. Larger molecules can have stronger van der Waals interactions, increasing the energy needed to separate them from other molecules. Therefore, the melting and boiling points of halogens increase with an increasing atomic radius and the size of molecules as you travel down the group 7 of the periodic table. Due to different melting and boiling points, fluorine and chlorine at room temperature are gases, bromine - liquid and iodine - solid.

Melting and boiling points of halogens

Electronegativity is the ability of an element to attract a pair of shared electrons in a bond. For example, if an atom of a less electronegative element, carbon, were to form a bond with a more electronegative fluorine, electrons that participate in bonding between them would be mainly surrounding the fluorine atom.

Going down the group 7 atomic radius increases. The shared electrons in covalent bonds with larger atoms get progressively further away from the nucleus and the atoms have a weaker attraction to them. Since electronegativity is the ability of an element to attract a pair of shared electrons in a bond, going down the group 7 electronegativity decreases.

Electronegativity of halogens

The neutral molecular halogens readily accept electrons, so they act as oxidising agents, taking electrons from other molecules. The negatively charged halide ions have spare electrons available, so they act as reducing agents, giving electrons to other molecules.

Oxidising agent is a particle that takes electrons from another molecule, oxidising it, while also being reduced itself. A reducing agent gives electrons to another molecule, reducing it, while also being oxidised itself. OIL RIG abbreviation presented in the image can help remember the definitions.

Going down the group 7 of the periodic table valence electrons are further away from the nucleus and are more easily removed to reduce another molecule. Thus, reducing ability of halide ions increases going down the group.

Going down the group 7 electrons from other particles are further away from the nucleus and have a weaker attraction to it. Thus, the oxidising ability of halogens increases going up the group. In fact, fluorine is such a strong oxidising agent that it can oxidise water.

A halogen can oxidise a less reactive halide. For example a reaction between bromide ions and chlorine would produce chloride ions and bromine:
Clβ‚‚ + 2Br⁻ β†’ 2Cl⁻ + Brβ‚‚.

Oxidising and reducing abilities of halogens

1

An Fβ€”Cl bond is formed and a diagram representing the distribution of electron density for it is shown in the image. Assign F and Cl to X and Y. Explain your answer

An Fβ€”Cl bond is formed and a diagram representing the distribution of electron density for it is shown in the image. Assign F and Cl to X and Y. Explain your answer

2

Which halide is the strongest reducing agent: F⁻, Br⁻, Cl⁻ or I⁻?

Which halide is the strongest reducing agent: F⁻, Br⁻, Cl⁻ or I⁻?

3

Explain why during reduction reaction of a chlorine molecule becoming a chloride ion, electrons need to be considered.

Explain why during reduction reaction of a chlorine molecule becoming a chloride ion, electrons need to be considered.

4

Explain how does the melting point change going down the group 7 of the periodic table.

Explain how does the melting point change going down the group 7 of the periodic table.

5

Why does electronegativity decrease going down the group 7 of the periodic table?

Why does electronegativity decrease going down the group 7 of the periodic table?

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