3.2.3 Group 7 (17) The Halogens Flashcards
What is a halide?
The negative ion of a halogen
X-
How does boiling point change descending group 7?
Boiling points increase going down the group.
This trend is shown by the changes of physical state from fluorine to iodine
Why does boiling point increase going down group 7
This is due to the increasing strength of van der waals forces as the size and relative mass of the molecules increases.
How does electronegativity change descending group 7?
Electronegativity decreases down the group
Why does electronegativity decrease down group 7?
Electronegativity is the tendency of an atom to attract a bonding pair of electrons. The halogens are all highly electronegative elements. But larger atoms attract electrons attract electrons less than smaller atoms. This is because the electrons are further from the nucleus and are shielded by more electrons.
Why do halogens get less reactive going down group 7?
When halogens react they gain an electron.
They get less reactive down the group, because the atoms become larger. The outer shell is further from the nucleus, so electrons are less strongly attracted to it.
The halogens become less oxidising descending the group
How can we observe the relative oxidising strength of halogens?
In displacement reactions, a halogen will displace a halide from solution if the halide is bellow it in the periodic table.
If a halide is displaced by a halogen then it was less oxidising than the halogen.
Why are displacement reations useful?
They can be used to determine the identity of a halide is present in a solution
What happens when you add chlorine water (colourless) to potassium chloride (colourless)?
No reaction
What happens when you add chlorine water (colourless) to potasium bromide (colourless)?
Orange solution (Br2 formed)
What happens when you add chlorine water (colourless) to potassium iodide solution (colourless)?
Brown solution (I2) formed
What happens when you add bromine water (orange) to potassium chloride (colourless)?
No reaction
What happens when you add bromine water (orange) to potassium bromide (colourless)
No reaction
What happens when you add bromine water (orange) to potassium ioddie (colourless)
Brown solution (I2) formed
What happens when you add iodine solution (brown) to potassium chloride (colourless)?
No reaction
What happens when you add iodine solution (brown) to potassium bromide (colourless)?
No reaction
What happens when you add iodine solution (brown) to potassium iodide (colourless)?
No reaction
How do you make bleach
By mixing chlorine gas with cold, diute, aqueous sodium hydroxide sodium chlorate(I) solution, NaClO(aq), aka bleach is formed
2NaOH(aq) + Cl2(g) -> NaClO(aq) + NaCl(aq) + H2O(l)
In this reaction, the oxidation state of chlorine goes up and down, therefore chlorine is both oxidised and reduced. This is called disproportionation
Name some uses for bleach
- Water treatment
- Bleaching paper and textiles
- Cleaning toilets
How does beach kill bacteria?
When chlorine is mixed with water it undergoes disportionation, you get a mixture of chloride and chlorate(I) ions:
Cl2(g) + H2O(l) <=> 2H+(aq) + Cl-(aq) + ClO-(aq)
In sunlight, chlorine can also decompose water to form chloride ions and water:
2Cl2(g) + 2H2O(l) <=> 4H+(aq) + 4Cl-(aq) + O2(g)
Chlorate(I) ions kill bacteria
Give the advantages of using chlorine to treat water
- It kills disease-causing microorganisms
- Some chlorine persists in the water and prevents reinfection further down the supply
- It prevents growth of algae, eliminating bad tastes and smells, removes discolouration caused by organic compounds
Give the risks of using chlorine to treat water
- Chlorine gas is very harmful if it’s breathed in - it irritates the respiritory system. Liquid chlorine on the skin or eyes cn cause severe chemical burns. Accidents involving chlorine can be serious and fatal
- Water contains a variety of organic compounds (e.g. from the decomposition of plants). Chlorine reacts with these compounds to form chlorinated hydrocarbons. Many chlorinated hydrocarbons are carcinogenic.
