Module 3.1.3 - The halogens
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What is common in halogens electron configuration?
All end in p5
What type of block are halogens in?
Halogens in p block - highest energy electron in a p orbital
What do halogens exist as?
diatomic molecules
What bonding exists in halogen molecules?
covalent bonding (between atoms)
What structure do halogens have?
simple covalent molecular (have induced dipole-dipole forces between molecules)
Why do halogens have low melting and boiling points?
Little heat energy is needed to break the weak induced dipole-dipole interactions between the molecules
Why do melting and boiling points increase as you go down the group?
• there are more shells, more electrons • there are more/stronger induced dipole-dipole interactions between the molecules • more (heat) energy is needed to break the stronger induced dipole-dipole attractions between the molecules
What type of agent are halogens?
Powerful oxidising agents (remove electrons from another species; reduced themselves)
What is oxidation power?
A measure of the strength with which a halogen atom is able to attract and capture an electron to form a halide ion
Which element is the strongest oxidising agent?
Fluorine
What happens to reactivity down group 7?
Reactivity decreases (oxidising power decreases) as; - atomic radius increases - there are more shells, greater shielding effect by inner shell electrons - there is a weaker nuclear attraction on outer shell electrons - nucleus is less able to attract and capture another electron into its outer shell
What are displacement reactions?
A reaction in which a more reactive halogen displaces a less halogen element from an aqueous solution of its halide ions
How is it able to tell if a displacement reaction has occurred?
The displaced halogen (X2) has its own characteristic colour, depending on the solvent
How are displacement reactions tested?
Each halogen solution, X2, is added to an aqueous solution of different halides and is shaken
What happens to chlorine (Cl2) when dissolves in water or organic solvent?
Turns pale green
What happens to bromine (Br2) when dissolved in water or organic solvent?
Turns orange
What happens to iodine (I2) when dissolved in water
turns brown
What happens to iodine (I2) when dissolved in organic solvent?
turns purple
What colour are halide ions?
colourless
What is shown in ionic displacement equations?
More reactive halogen becomes its halide e.g Cl2 + 2I- -> 2Cl- + I2
What are disproportionation reactions?
a reaction in which the same element is both oxidised and reduced
What does chlorine react with water to form?
Chloric (I) acid (chlorine water) and hydrochloric acid Cl2(aq) + H2O(l) -> HClO(aq) + HCl(aq)
How the reaction between chlorine and water disproportionation?
Chlorine is both oxidised and reduced
Why is chlorine advantageous?
Kills bacteria (added to drinking water, swimming pools etc.)