Group 2 & Group 7

What are the states and colours of the halogens

• fluorine: gas = pale yellow

• chlorine: gas = pale green

• bromine: liquid = orange

• iodine: solid = purple (brown as liquid)

What is meant by an oxidising agent

• oxidise other species, is reduced itself

• halogens act as oxidising agents by gaining one electron

What is the trend in reactivity going down the halogen group

• reactivity decreases as oxidising power also decreases

• atomic radius increases

• more electron shielding

• less nuclear attraction for outer electrons

• ability to gain an electron decreases

What is the strongest oxidising agent and why

• fluorine

• has smallest atomic radius and the least amount of shielding

• stronger nuclear attraction to outer electron

• able to gain an electron very easily

What are the three displacement reactions of the halogens

• chlorine + potassium bromide → potassium chloride + bromine

• chlorine + potassium iodide → potassium chloride + iodine

• bromine + potassium iodide → potassium bromide + iodine

Write the ionic equation for chlorine and potassium bromide

state the colour of the solution and what has been oxidised and reduced

• Cl2 + 2Br- → 2Cl- + Br2

• orange

• Cl is reduced, Br is oxidised

• Cl is the STRONGER OXIDISING AGENT

Write the ionic equation for chlorine and potassium iodide

state the colour of the solution and what has been oxidised and reduced

• 2Cl + 2I- → 2Cl- + I2

• brown

• Cl is reduced, I is oxidised

• Cl is the STRONGER OXIDISING AGENT

Write the ionic equation for bromine and potassium iodide

state the colour of the solution and what has been oxidised and reduced

• Br2 + 2I- → 2Br- + I2

• brown

• Br is reduced, I is oxidised

• Br is the STRONGER OXIDISING AGENT

What colours do the halogens turn when cyclohexane (organic solvent) is added

(this is added to further distinguish colours between Br2 and I2)

• Cl: remains pale green

• Br: remains orange

• I: turns lilac/violet/purple

What is the test for halides and what are the positive results

• add dilute nitric acid and add silver nitrate

• chloride ions: white precipitate

• bromide ions: cream precipitate

• iodide ions: pale yellow precipitate

Write the ionic equations for the halide tests

• Ag+ (aq) + Cl- (aq) → AgCl (s)

• Ag+ (aq) + Br- (aq) → AgBr (s)

• Ag+ (aq) + I- (aq) → AgI (s)

What happens when dilute ammonia is added to the tested halides

• AgCl dissolves

• CREAM PPT: AgBr remains insoluble

• YELLOW PPT: AgI remains insoluble

What happens when concentrated ammonia is added to the tested halides

• AgCl dissolves

• AgBr dissolves

• YELLOW PPT: AgI remains insoluble

What is the trend in atomic radius down group 2

• atomic radius increases

• as number of electrons increase, so number of shells increase

• increase in shielding

What is the trend in first ionisation energy down group 2

• 1st IE decreases

• as atomic radius increases

• shielding increases

• weaker nuclear attraction between outer e-s and nucleus

• so outer electron is removed more easily as less energy required

Why is the 2nd IE greater than the first IE

• same number of protons attracting one fewer electron

• second electron is being removed from a positively charged ion

• greater nuclear attraction in the ion between nucleus and remaining outer e-s

What is the trend in MP down group 2

(Mg EXCEPTION)

• general decrease in MP

• increased atomic radius & increase in shielding

• weaker electrostatic attraction between the nucleus and sea of delocalised electrons

• so less energy required to overcome the weaker EFs

What is the trend in reactivity down group 2

• reactivity increases as elements become more reducing

• atomic radius increases

• more shielding

• weaker nuclear attraction for the outer electrons

• ability to lose outer electrons increase

What is the strongest reducing agent and why

• Barium

• Has largest atomic radius

• Most amount of shielding

• Weaker nuclear attraction to the outer electrons

• Is able to lose to lose outer electrons more easily

What are the colours of the group 2 metals in flames

• Magnesium: bright white

• Calcium: orange red

• Strontium: red

• Barium: green

What are the equations for the reactions of group 2 metals with oxygen

• 2Mg + O2 → 2MgO

• 2Ca + O2 → 2CaO

• 2Sr + O2 → 2SrO

• 2Ba + O2 → 2BaO

  • REDOX reactions where metal is oxidised from 0 → +2

What are the general equations for the reactions of group 2 metals with water

• Mg (s) + 2H2O (l) → Mg(OH)2 (s) + H2 (g)

• Ca (s) + 2H2O (l) → Ca(OH)2 (s) + H2 (g)

• Sr (s) + 2H2O (l) → Sr(OH)2 (aq) + H2 (g)

• Ba (s) + 2H2O (l) → Ba(OH)2 (aq) + H2 (g)

What is the exception for the reaction of Mg with water

• Mg is usually reacted with gaseous H2O rather than liquid H2O as the reaction is faster

• Mg (s) + 2H2O (g) → Mg(OH)2 (s) + H2 (g)

Which metal reacts the most vigorously and what are two observations which show this

• Ba

• Fizzes more vigorously

• Disappears / dissolves faster

What are the equations of group 2 metals with acids

• Mg + 2HNO3 → Mg(NO3)2 + H2

• Ca + 2HCl → CaCl2 + H2

• Sr + 2HCl → SrCl2 + H2

• Ba + H2SO4 → BaSO4 + H2

What are the equations of group 2 metals with chlorine

• Mg + Cl2 → MgCl2

• Ca + Cl2 → CaCl2

• Sr + Cl2 → SrCl2

• Ba + Cl2 → BaCl2

What happens when oxides react with and dissolve in water (OXIDE=BASE)

• reacts with water to form a solution of the metal hydroxide

  • MgO(s) + H2O(l) → Mg(OH)2(aq)

  • typical pH ≈ 10-12

• dissolves in water to form alkaline solutions

  • Mg(OH)2 + aq → Mg2+ + 2OH- (aq)

What happens with the hydroxides are you go down group 2 (HYDROXIDE=BASE)

• Solubility increases

• This results in more OH- going into the solution

• So alkalinity also increases

What are uses of hydroxides

• used to combat acidity to their alkalinity

  • Ca(OH)2: used by farmers to neutralise acidic soils

  • Mg(OH)2: used in indigestion remedies to neutralise excess stomach acid

How do group 2 carbonates react and what products are formed

• decompose by thermal decomposition

• a metal oxide + CO2 gas is formed

  • MgCO3 (s) → MgO (s) + CO2 (g)

What with the carbonates as you go dow group 2

• the carbonates are more difficult to decompose as group descends

• ease of thermal decomposition decreases

What is the equation of chlorine with water and what is it used for

• Cl2 (g) + H2O (l) → HCl (aq) + HClO (aq)

• HClO: chloric (I) acid

• used for sterilisation

• Cl shows disproportionation

What are the advantages and disadvantages of chlorine and water for sterilisation

• +: kills bacteria

• -: chlorine is toxic

What is the equation for making bleach and what conditions are required

• Cl2 (g) + 2NaOH (aq) → NaClO (aq) + NaCl (aq) + H2O (l)

• NaOH must be cold and dilute

• Na+ + ClO- → NaClO (bleaching agent)

What is the ionic equation for making bleach

• Cl2 (g) + 2OH- (aq) → ClO- (aq) + Cl-(aq) + H2O (l)

Write the formulas for:

• sodium chlorate (V)

• sodium chlorate (III)

• NaClO3

• NaClO2

What is the test for sulfates and what is the ionic equation

• add dilute hcl and barium chloride

• white precipitate formed

• Ba2+ (aq) + SO4 2- (aq) → BaSO4 (s)

What is the test for carbonates and what is the ionic equation

• add dilute acid and bubble gas through limewater

• limewater turns cloudy/milky

• CO3 2- (aq) + 2H+ (aq) → CO2 (g) + H2O (l)

What’s the test for ammonium ions and what’s the equation

• add aq NaOH and heat

• hold red litmus paper → turns blue

• NH4+ (aq) + OH (aq) → NH3 (g) + H2O (l)