Trend in reactivity of group 2 metals?
- Down the group, reactivity increases
- Larger atomic radius and shielding effect
- Nuclear attraction to outer shell electrons decreased
- Easier to lose electrons
- Become stronger reducing agents
Reaction of Group 2 metals with O2?
M(s) + O2(g) -> MO(s)
Reaction of Group 2 metals and oxides with H2O
M(s) + 2H2O(l) -> M(OH)2(aq/s) + H2(g)
MO(s) + H2O(l) -> M(OH)2(aq/s)
Reaction of Group 2 metals, oxides and hydroxides with dilute acids (e.g. HCl)
M(s) + 2HCl(aq) -> M(Cl)2(aq) + H2(g)
MO(s) + 2HCl(aq) -> M(Cl)2(aq) + H2O(l)
M(OH)2(s) + 2HCl(aq) -> M(Cl)2(aq) + 2H2O(l)
Trend in solubility of Group 2 metal oxides?
- Solubility increases down the group
- This is because larger ions form weaker ionic bonds (larger atomic radius)
- G2 metal oxides are only partially soluble in solution
Uses of Group 2 compounds?
- As antacids (Mg(OH)2, CaCO3)
- To neutralise acidic soil (Ca(OH)2)
Trend in boiling points of halogens?
- Increases down the group
- Atoms become larger, contain more electrons
- Thus, have stronger London forces between molecules, which require more energy to break
Describe the appearance of F2 at rtp
Pale yellow gas
Describe the appearance of Cl2 at rtp, and aqueous/dissolved in an organic solvent
Pale green gas, green in solution
Describe the appearance of Br2 at rtp, and aqueous/dissolved in an organic solvent
Brown liquid, orange in solution
Describe the appearance of I2 at rtp, and aqueous/dissolved in an organic solvent
Grey-black solid, brown when aqueous, purple in organic solvent
Trend in reactivity of halogens?
- Decreases down the group
- Larger atomic radius and shielding effect
- Nuclear attraction to outer shell electrons decreased
- Harder to gain electrons
- Become weaker oxidising agents
Define dispropotionation
When an element is both oxidised and reduced
Reaction between Cl and H2O
Cl2(g) + H2O(l) -> HCl(aq) + HClO(aq)
HClO is a weak bleach used in swimming pools/water treatment
Reaction between Cl and NaOH
Cl2(g) + 2NaOH(aq) -> NaCl(aq) + NaClO(aq) + H2O(l)
NaClO is household bleach
Benefits and risks of chlorine in water treatment
Benefits: Effective disinfection of water, prevents disease
Risks: Chlorine gas is toxic, production of toxic chlorinated hydrocarbons (on reaction with methane in water)
Carbonate test
Add dilute nitric acid
CO3^2-(aq) + H+(aq) -> H2O(l) + CO2(g)
CO2 gas is produced
Sulphate test
Add barium nitrate
SO4^2-(aq) + Ba^2+(aq) -> BaSO4(s)
White precipitate is formed
(must be filtered before further testing)
Halide test
Add silver nitrate
Hal^-(aq) + Ag^+(aq) -> AgHal(s)
Cl^- = white precipitate, dissolves in dilute ammonia solution
Br^- = cream precipitate, dissolves in concentrated ammonia solution
I^- = yellow precipitate, doesn’t dissolve in ammonia solution
Ammonium test
Add warm NaOH solution
NH4+(aq) + OH^-(aq) -> NH3(g) + H2O(l)
Test with damp litmus paper
Colour change from yellow to blue
