The Halogens

Why does the boiling point increase down the group?

Because the molecules become larger in size, this allows for stronger induced dipole dipole forces to develop between molecules. These stronger intermolecular forces require increasing amounts of energy to overcome.

What is electronegativity?

The tendency of an atom to attract a bonding pair of electrons

Why does electronegativity of halogens decrease down the group?

Nuclear charge increases down the group as more protons are added increasing attraction for electrons. Atomic radius increases down the group as more electron shells and more shielding which have a greater effect then nuclear charge

Why does halogen reactivity decrease down the group?

Due to increase in atomic radius and shielding outweighs the increase in nuclear charge so it becomes harder for larger halogens to attract the electrons needed to form a negative ion

Why does the reducing power of halides increase down the group?

Due to the increase in ionic radius and shielding outweighs the increase in nuclear charge so it becomes easier for larger halides to lose electrons and become oxidised

How to test for halides?

1. Add dilute nitric acid to the sample to remove any ions like carbonates that may interfere by also forming precipitates with silver nitrate

2. Add silver nitrate solution and silver ions will react with halide ions to form silver halide precipitate which can be observed as a colour change depending on the halogen, chloride= white, bromide= cream, iodide= yellow

As some of the halides have similar colours how else could u better identify them?

Add excess ammonia solution as silver halides have different solubilities in dilute and concentrated ammonia solution. Chloride dissolves in both, bromide remains insoluble in dilute and dissolves in concentrated, iodide remains insoluble in both

What are three benefits and two risks of using chlorine for water disinfectant?

Benefits= kills disease causing microorganisms, prevents reinfection further down the supply, removes bad tastes, smells and discolouration

Risks= chlorine gas causes severe irritation if inhaled, it reacts with organics to form carcinogenic chlorinated hydrocarbons

What could be used instead of chlorine to sanitise the water? But why arent they used?

Ozone or UV light. However ozone is expensive and decays rapidly and UV is less effective in cloudy water

How to confirm the presence of carbonate ions?

1. Add dilute nitric acid to your sample

2. Observe for effervescence caused by bubbling of co2 gas

3. If bubbling occurs pass through lime water in a connecting tube and if co2 is present the limewater will turn cloudy due to white calcium carbonate precipitate being formed

How to test for sulfate ions?

1. Add dilute nitric acid to your sample

2. Add a few drops of aqueous Ba2+ ions to the sample

3. Observe for a white precipitate of barium sulfate forming