Group 7

• The elements of group 7 are known as the Halogens
• Astatine is rare and radioactive and so generally not considered when looking at properties
• Halogens form 1- ions to achieve a noble gas configuration
• When group 7 elements exist under normal conditions they are all diatomic molecules and are called halogens
• when group 7 elements have gained an electron to form a 1- ion they are called halides
• At room temperature fluorine is a pale yellow gas
• At room temperature chlorine is a green gas
• At room temperature bromine is an orange/brown liquid which vaporises easily into an orange gas
• At room temperature iodine is a black solid which vaporises on heating to a purple gas
• The elements of group 7 become darker and denser going down group 7
• Fluorine has a number of properties unusual in comparison to other Halogens. This is because the F - F covalent bond is surprisingly weak. This is because the fluorine atoms being very small mean that the non bonding pairs of electrons on the outer shells are held so close to one another they begin to repel each other
• The atoms get bigger descending group 7 because each additional element has an extra electron shell
• Electronegativity decreases going down group 7 due to a larger atomic radius and more shielding
• Halogens are non-polar meaning the only intermolecular force existing between halogen molecules are Van Der Waals
• The strength of the intermolecular forces are dependent on the size of the molecule, so F2 has the lowest melting and boiling point and I2 has the highest melting and boiling point
• Reduction is defined as the gain of electrons. Halogens get reduced, and can act as oxidising agents
• Fluorine accepts electrons most easily and so is the strongest oxidising agent. Oxidising power decreases down group 7
• Halogens can take part in displacement reactions with other halide ions. The elements highest up group 7 forms a halide ion and the halogen lowest down group 7 forms a halogen molecule
• If Br2 is formed as a product in a displacement reaction, the mixture will turn a brown/orange colour
• If I2 is produced during a displacement reaction, a black solid will form
• Hydrogen fluoride gas is dangerous and is used to etch glass
• As elements they are known as halogens. As ions they are known as halides
• Molecules are held together by Van der Waals forces. The more mass the elements have and therefore greater size, surface area and number of electrons, the stronger the van der Waals forces, and more energy is needed to overcome the forces
• Displacement reactions cannot be done aqueously with fluorine, as it is so reactive it will also react with the water
• A disproportionation reaction is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states