Reactivity trends Flashcards
What is the most common reaction with group 2?
Redox (reducing agent as the other species gains electrons and is reduced)
What is the trend of reactivity in group 2?
Down the group, reactivity increases because the atomic radius increases so more shielding. Attraction decreases and it is easier to remove electrons.
What are the reactions of group 2?
With H2O –> alkaline hydroxide M(OH)2 + H2.
Fizzing, metal dissolves, increasing temperature, white precipitate (Ca).
With dilute acids –> salt + H2
What happens to IE down group 2?
1st and 2nd IE decreases as the attraction of the nucleus and outer electrons decreases due to increased radius and shielding.
What are reactions of group 2 oxides and hydroxides?
Oxides react with water, release OH- and forming alkalis. Down the group, oxides form stronger alkalis as hydroxides are more soluble.
Hydroxides are partially soluble in water - when saturated, any more forms a solid precipitate.
What are uses of group 2 compounds?
- Ca(OH)2 is fairly soluble so is used to neutralise acidic soils
- aq Ca(OH)2 is limewater - test for CO2
- Mg(OH)2 + CaCO3 are used as antacids - neutralisation.
What is the trend in melting point down group 7?
Increases as it is bigger - more electrons so bigger London’s forces between molecules so more energy to break.
All react by gaining 1 electron in redox - each atom reduced so it is an oxidising agent.
What are halogens and halide ions?
Halogens = oxidising agents
Halide ions = reducing agents
What is the trend in reactivity down group 7?
Decreases because bigger atoms with increased shielding so less attract electrons - harder to form ions down the group.
Fluorine is the strongest oxidising agent.
What is disproportionation?
A redox reaction where the same element is oxidised and reduced.
What are examples of disproportionation reactions?
Cl2 + H2O –> HClO + HCl
Cl2 + 2NaOH –> NaClO + NaCl + H2O
What are the pros and cons of treating water with chlorine?
Pros:
Kills dangerous pathogens
Less bad smells/tastes
Removes bacteria/algae
Cons:
Disinfection by-products
Ineffective with some microbes
Risks of some cancers
What is the test and results for halide ions?
Dilute nitric acid and silver nitrate solution.
aq silver ions to form silver halide precipitates.
Cl- is white
Br- is cream
I- is yellow
How can you tell the difference between halide ions better?
Dilute ammonia, then concentrated. Cl- dissolves in dilute
Br- dissolves in concentrated
I- is insoluble
What is the test for carbonate ions?
Dilute nitric acid - if bubbles, bubble through limewater.
