Group 7 Flashcards
Name the elements in group 7
The elements in group 7 are fluorine, chlorine, bromine, iodine and astatine.
What colour and state is fluorine?
Fluorine – poisonous yellow gas
What colour and state is chlorine?
Chlorine – poisonous, dense, yellow-green gas
What colour and state is bromine?
Bromine – caustic and toxic red-brown volatile liquid. Forms red-brown vapour.
What colour and state is iodine?
Iodine – shiny grey-black solid. Sublimes to form violet vapour on heating.
What colour and state is Astatine?
Astatine – maybe dark, likely to have higher melting point than Iodine. So radioactive and short half life no one knows!
What colour is chlorine in solution?
Chlorine – pale green
What colour is bromine in solution?
Bromine – orange
What colour is iodine in solution?
Iodine – pale yellow (brown in Iodide ions)
What is the trend in colour going down the group?
The colour gets darker
What is the trend in atomic radius going down the group and why?
The atomic radius increases. (There are MORE energy levels, outer electron is further away, size increases)
What is the trend in reactivity going down the group and why?
Reactivity decreases. (outer electron is further away, increased shielding, weaker attraction between nucleus and incoming electron).
What is the trend in boiling point going down the group and why?
Boiling point increases. (size increases, more electrons, greater induced dipole-dipole attractions, more energy needed to overcome the van der Waals forces)
What is the trend in electronegativity going down the group and why?
Electronegativity decreases ( the bonding electrons are closer to the positive nucleus in smaller atoms, less shielding, strong positive nucleus attracts bonding pair more strongly).
Why are halogens diatomic?
Halogens are all diatomic due to having one covalent bond.
What is the trend in mean bond energies going down the group and why?
The mean bond enthalpy decreases as atomic number increases (as the bonding electrons are further from the nucleus).Apart from Fluorine as they are so close together that the lone pairs repel and weaken the bond.
What is the trend in reducing power going down the group and why?
Reducing power increases as atomic number increases.They are oxidised themselves. Down the group: Radius increases Shielding increases
What is the trend in oxidising power going down the group and why?
Oxidising power decreases as atomic number increases. They are reduced themselves. Down the group: Radius increases.Shielding increases
How does chlorine react with sodium hydroxide?
Chlorine reacts with cold, dilute aqueous sodium hydroxide to form sodium chlorate (I) NaClO and Sodium chloride NaCl.
How do the rest of the halogens react with sodium hydroxide?
The rest of the halogens react the same way with the same formula.
Give the ionic equation for the reaction of chlorine with sodium hydroxide.
2OH- + Cl2 -> Cl- + ClO- + H2O
Give the symbol equation for the reaction of chlorine with sodium hydroxide.
2NaOH + Cl2 -> NaCl + NaClO + H2O
What would you see when chlorine reacts with sodium hydroxide?
Yellow-green gas forms a colourless solution
What colour solution does Chlorine make in water?
Chlorine makes a pale green solution in water.
Give the equation for the reaction of chlorine with water.
Cl2(g) + H2O(l) -> HCl(aq) + HClO(aq)
Give the equations for the reaction of chlorine with water in sunlight
2Cl2(g) + 2H2O(l) -> 4HCl(aq) + O2(g)
What happens when the halogens react with each other?
The more reactive halogens displace the less reactive halogens from solution.
Give the ionic equation for the reaction between chlorine and bromide ions.
Cl2 + 2Br- -> 2Cl- + Br2
Give the half equations for the reaction between chlorine and bromide ions.
Cl2 + 2e- -> 2Cl-
What happens when you add concentrated sulphuric acid to bromide ions?
When added to solid bromide compound misty white fumes (hydrogen bromide) along with some brown gas (bromine).
What happens when you add concentrated sulphuric acid to iodide ions?
When added to solid iodide compound misty white fumes (hydrogen iodide) are released, purple fumes (iodine gas) a black solid is formed (iodine) and rotten egg smell (H2S gas)
Why is concentrated sulphuric acid usually used to test for halides?
This isn’t usually used as conc sulphuric acid is corrosive and toxic gases are formed.
Why when testing for halide ions do you use nitric acid before adding silver nitrate?
Nitric acid is used to remove other ions that would react with the silver ions and form precipitates like CO32-, SO32-, OH-.
What colour precipitate is formed with silver nitrate and fluoride ions?
Fluoride doesn’t produce a precipitate.
What colour precipitate is formed with silver nitrate and chloride ions?
Chloride – White precipitate
What colour precipitate is formed with silver nitrate and iodide ions?
Iodide – Cream precipitate
What colour precipitate is formed with silver nitrate and bromide ions?
Bromide – Yellow precipitate
Give the ionic equation for the reaction between silver nitrate and sodium chloride.
Ag+(aq) + Cl-(aq) -> AgCl(s)
Give the full equation for the reaction between silver nitrate and sodium chloride.
AgNO3(aq) + NaCl(ag) -> AgCl(s) + NaNO3(aq)
What happens to the silver chloride precipitate when you add ammonia solution?
Silver chloride dissolves in dilute and concentrated.
What happens to the silver bromide precipitate when you add ammonia solution?
Silver bromide dissolves in concentrated only.
What happens to the silver iodide precipitate when you add ammonia solution?
Silver Iodide doesn’t dissolve in either.
What does acidified barium chloride solution test for?
Tests for sulfate ions.
How would you test for sulfate ions?
Add solid sample to hydrochloric acid and barium chloride.
What is a positive test result for sulfate ions?
White precipitate is BaSO4
What does dilute nitric acid test for?
Tests for carbonate ions
How would you test for carbonate ions?
Add solid to the acid.
What is a positive test result for carbonate ions?
Effervescence (CO2), sold disappears, gas can be bubbled through limewater and will turn cloudy.
What is magnesium nitrate or chloride solution test for?
Tests for carbonate ions (rules out hydrogen carbonate)
How would you test for carbonate ions? (to rule out hydrogen carbonate)
Add solid to deionised water add the magnesium solution.
What is a positive test result for carbonate ions? (not hydrogen carbonate)
White precipitate (MgCO3)
What does sodium hydroxide solution test for?
Tests for metal cations.
How would you test for metal cations?
Dissolve a spatula in deionised water, add a few drops of NaOH then about 5cm3 (x.s.)
What is a positive test result for metal cations?
White precipitate is magnesium hydroxide or calcium hydroxide.
How would you test for ammonia?
Place in a test tube with the solid sample and sodium hydroxide. Warm gently.
What is a positive test result for ammonia?
Test gas with damp red litmus paper. Paper changes to blue.
How can you use hydrochloric acid to test for ammonia?
Dip a glass rod into concentrated hydrochloric acid. White ammonium chloride gas produced.
