Group 7 Flashcards
Explain the trend in size of atom down group 7
Atoms get bigger because each element has one extra filled main level of electrons compared with the one above it
Explain the trend in electronegativity down group 7
The atoms get larger down the group meaning the shared electrons are further from the halogen nucleus and the sheilding increases by more levels of electrons. These features are more important than the nuclear charge
Explain the trend in melting and boiling points as you go down group 7
These increase as you go down the group because larger atoms have more electrons and makes the van deer walls forces between the molecules stronger meaning alot more energy is required to break these
Describe the visual appearance of flourine
It is a very pale yellowish gas that is highly reactive
Describe the visual appearance of bromine
Red liquid that gives off brown fumes
Describe the visual appearance of chlorine
Greenish reactive gas
Describe visual appearance of iodine
Shiny grey solid that sublimes to purple gas
Why may flourine have unusual properties
The F-F bond is unexpectedly weak compared to the other halogens
What is the trend in oxidising ability down group 7?
It decreases down the group
How can displacement reactions happen with group 7 elements
A halogen that is a strong oxidising agent will displace a halogen that has a lower oxidising power from one of its compounds
Describe the observations you would see if you saw group 7 element in a displacement reaction
The colour of the solution in the test tube shows which halogen is free in the solution. If the chlorine is free the colour will be very pale green, if it is bromine the colour will be yellow if it is iodine the colour will be brown with a black solid sometimes being present
Show the ionic equation of chlorine displacing bromine in a displacement reaction
Cl2 + 2Br- = 2CL- +Br2
All aq
Show the ionic equation of chlorine displacing iodine in a displacement reaction
Cl2 + 2I- = 2Cl-+ I2
All aq
Show the ionic equation of bromine displacing iodine in a displacement reaction
Br2+ 2I-= 2Br- + I2
All aq
Describe the trend in the halide groups reducing ability
Increases down the group because the larger the ion, the more easily it will lose an electron. This is because the electron is lost from an outer shell that is further away from the nucleus as the ion gets larger so the electrostatic attraction is less
What is observed when sodium flouride reacts with concentrated sulfuric acid
F- ion is not strong enough as a reducing agent to reduce the S in H2S04, meaning no redox reactions occur as no oxidation states change. Only acid base reactions occour
NaF(s) + H2S04(l) = NaSO4(s) + HF(g)
White steamy fumes of HF are evolved
What is observed when sodium chloride reacts with concentrated sulfuric acid?
Around the same reducing ability as floruine, although it is slightly stronger, it still doesnt have the ability to reduce the sulfur
Nacl(s) + H2SO4(l)= NaHS04 (s) +HCL
White steamy fumes of HCL are formed
Describe the reaction of sodium bromide when it reacts with concentrated sulfuric acid
These are stronger reducing agents than F and CL so they reduce the S in sulfuric acid
2 reactions happen -
Sodium hydrogensulfate and hydrogen bromide are produced in an acid base reaction
NaBr(s) + H2S04(l) = NaHSO4(s) + HBr(g)
They are strong enough reducing agents to reduce the sulfuric acid to sulfur dioxide. oxidation state of sulfur reduces from +6 to +4 and the oxidqation state of the bromine increases from -1 to 0
2H+ + 2Br + H2S04 = Br2(g) + S02(g) + 2H20(l)
Give the acid base reaction and the redox combined overall equation for the reaction of bromine with concentrated sulfuric acid
2NaBr + 3H2S04 = 2NaHS04 + S02 + Br2 + 2H20
What is observed when bromine reacts with concentrated sulfuric acid
White steamy fumes of HBr are evolved
Orange bromine fumes evolve
Colourless acidic gas is also formed S02
Exothermic reaction
Some of the bromine vapourises
Give the redox half equations for the second step of the reaction between bromine and conc sulfuric acid
Ox half equation 2Br- = Br2 + 2e-
Re half eqaution H2S04 + 2H+ + 2e- = S02 + 2H20
Describe the observations made when iodine reacts with conc sulfuric acid
Iodine ions are the strongest halides as reducing agents , they can reduce the sulfur from +6 in H2S04 to +4 in S02 to 0 in S and -2 in H2S
White steamy fumes of HI are evoved
Black solid and purple fumes of iodine are evolved
A colourless acidic gas S02
A yellow solid of sulfur
H2S , hydrogen sulfide a gas with a bad egg smell
Describe the reactions that result in the observations saw when iodine reacts with conc sulfuric acid
NaI(s) + H2S04(l) = NaHS04(s) + HI(g)
2H+ 2I- + H2 s
What is a disproportionation reaction
A type of redox reaction where the oxidation number of some atoms of the same element increases and others decrease
When does chlorine take part in a reaction with water?
When chlorine is used to purify water for drinking and in swimming baths to prevent life threatening diseases, as the chloric acid formed from this is an oxidising agent and kills bacteria by oxidising it. It is also a bleach
The benefits of heath water treatment by chlorine outweigh its toxic effects
Give the reaction of chlorine with water in normal conditions
Cl2 (g) + H20(l)= HCL0(aq) + HCL(aq)
The oxidation number of one of the chlorine atoms increases from 0 to +1 and the oxidation number of another chlorine atom decreases from 0 to -1 (Disporportionation)
This is a reversible reaction
Give and explain the reaction of chlorine and water in sunlight
2Cl2(g) + 2H20(l) = 4HCl( aq) + 02 (g)
Chlorate (I) ion will decompose to produce hydrochloric acid and oxygen
2HCl0 ( aq) = 2HCL( aq) + 02 (g)
In this reaction chlorine is rapidly lost from pool water in sunlight so shallow pools need frequent addition of chlorine
The greenish colour of chlorine water fades as the Cl2 reacts and a colourless gas is produced ( 02)
What is observed when universal indicator is added to the solution of chlorine and water?
It will first turn red due to the acidity of both reaction products, and it will then turn colourless as HCl0 bleaches the colour
Describe and explain the reaction when chlorine reacts with cold dilute sodium hydroxide solution
Cl2(g) + 2NaOH( aq) = NaClO(aq) + NaCl(aq) + H20
This forms sodium chlorate (I) , NaClO. This is an oxidising agent and the active ingredient in household bleach
This is a disproportionation reaction
When each atom of the same element in a compound of the redox reaction either increases in oxidation state or decreases
The oxidation state of Cl decreases in the product NaCl(aq) however it increases in the product NaClO(aq)
