Group 7 reactions Flashcards
What type of agents do most halogens normally act as?
Oxidising agents (oxidise other elements by making them lose electrons)
And gaining these electrons to be reduced themselves
Halogen atoms are normally… (in a reaction)
Reduced to gain electron and complete outer shell
Halogens reaction with less reactive halide compounds
A displacement reaction in which a more reactive halogen can displace a less reactive halide ion from its compound
Trend in displacement reaction
More reactive element (aka the one with higher oxidising ability to gain electrons and better ability to gain electrons) ABOVE IT in the group will DISPLACE ones BELOW IT
What type of reaction is displacement reaction and why?
Redox because
The more reactive halogen which does displacing is reduced (gains electrons to form compound)
Less reactive halide ion which IS displaced loses electrons to form halogen molecule in pure form
Reducing power of halide ions
How easily a halide ion can be oxidised
By losing electrons as an ion to form a halogen atom
How can we see what halogen was made in a reaction?
Add a few drops of hexane
Which will form organic layer over aqueous and the colour change will determine what halogen is made
How does oxidising power change down the group?
Going down the group, oxidising power (ability to be reduced thus gain electrons) decreases
Why does the oxidising power decrease down the group?
Because the ability for halogen to gain an electron decreases down the group as the atomic radii increases
Which increases no of electrons thus increases amount of shielding electron experiences
Furthermore with more shells, electron is at further distance so by experiencing less nuclear force will not be gained as easily
OVERCOMES INCREASE IN PROTON NUMBER
Reducing ability
The ability for a halide ion to reduce another element by losing electrons (to be oxidised themselves) and making this element gain electrons
How does the reducing ability change down the group?
Increases down the group of halide ions
Why does reducing ability increase down a group of halide ions?
Reducing ability = ability to lose electrons and be oxidised
Going down the group, the atomic radii increases so number of electrons increase which increases shielding of outer shell electrons, furthermore electrons are further away from nucleus so in total will experience less nuclear attraction and as a result can be lost easier going down
Halogens + group 1 and 2 and 3 metals
Forms a metal salt
When a group 1,2,3 reacts with halogen what is oxidised (loses electrons)?
The group1,2,3 metal by losing outer shell electrons to form a cation
When a group 1,2,3 reacts with halogen what is reduced (gains electrons)?
The halogen because it gains metals donated electrons (acts as oxidising agent) to form a halide ion and form a salt
Most common oxidation states of halogens
Most common and stable is -1 because usually acts as oxidising agent where it makes something lose electrons to gain it =-1
Chlorate (I) and bromate (I) oxidation state
ClO⁻
BrO⁻
Oxidation state for each halogen atom as a result would be +1
Bromate (III) oxidation state
BrO₂⁻
Oxidation state for bromine atom as a result is +3
Iodate (V) oxidation state
IO₃⁻
Oxidation state for iodine atom as a result is +5
Iodate (VII) oxidation state
IO₄⁻
Oxidation state for iodine atom as a result is +7
What does pure halogen + cold alkali make?
A metal hypohalide (which is metal + O + halogen atom such as NaOCl known as sodium hypochlorite)
A metal halide such as NaCl
And water
Chlorine + COLD sodium hydroxide (alkali)
Cl₂ + 2NaOH —> NaOCl + NaCl + H₂O
What does chlorine + cold sodium hydroxide make?
Sodium hypochlorite which is bleach
Uses of bleach
Water treatment, cleaning toilets etc
What type of reaction is halogen + cold alkali?
A disproportionation reaction
Because the halogen atom has been reduced (gained electrons) to form halide ion in metal salt
And has been oxidised (lost electrons) to form a halogen ate ion
What does pure halogen + hot alkali make?
A metal halogenate (metal+halogen+O₃) + metal halide + water
Chlorine + HOT sodium hydroxide
Makes NaClO₃ + 5NaCl + 3H2O
Sodium hypochlorite formula
NaClO
What is sodium hypochlorite made from?
Chlorine + cold sodium hydroxide
Sodium chlorate formula
NaClO₃
What is sodium chlorate made form?
Chlorine + hot sodium hydroxide
Chlorine + water
Forms hydrochloric acid + hypochlorous acid (HClO)
Sodium hypochlorite vs hypochlorous acid
Sodium hypochlorite (NaClO)= made from mixing chlorine and cold sodium hydroxide
Hypochlorous acid (HClO) = made from mixing chlorine and water
Hypochlorous acid
HClO
What does adding hypochlorous acid to water form?
hypochlorote ion ClO- and a hydronium ion H₃O⁺
